REVIEW ARTICLE
Vacuolar protein sorting mechanisms in plants
Li Xiang1, Ed Etxeberria2 and Wim Van den Ende1
1 Laboratory of Molecular Plant Biology, KU Leuven, Belgium
2 Horticulture Department, Citrus Research and Education Center, University of Florida, Lake Alfred, FL, USA
Keywords
adaptor protein complex; BP80;
endomembrane; ER body; Golgi; protein
storage vacuole; signal peptide; sorting;
trafficking
Correspondence
W. Van den Ende, Laboratory of Molecular
Plant Biology, KU Leuven, Kasteelpark
Arenberg 31, Leuven, Belgium
Fax: +32 16321967
Tel: +32 16321952
E-mail: wim.vandenende@bio.kuleuven.be
(Received 14 July 2012, revised 8
November 2012, accepted 11 December
2012)
Plant vacuoles are unique, multifunctional organelles among eukaryotes.
Considerable new insights in plant vacuolar protein sorting have been
obtained recently. The basic machinery of protein export from the endoplasmic reticulum to the Golgi and the classical route to the lytic vacuole
and the protein storage vacuole shows many similarities to vacuolar/lysosomal sorting in other eukaryotes. However, as a result of its unique functions in plant defence and as a storage compartment, some plant-specific
entities and sorting determinants appear to exist. The alternative postGolgi route, as found in animals and yeast, probably exists in plants as
well. Likely, adaptor protein complex 3 fulfils a central role in this route.
A Golgi-independent route involving plant-specific endoplasmic reticulum
bodies appears to provide sedentary organisms such as plants with extra
flexibility to cope with changing environmental conditions.
doi:10.1111/febs.12092
Introduction
A typical plant or animal cell contains up to 10 000
different types of proteins, whereas a yeast cell contains approximately 5000. For proper functioning,
each of these numerous proteins must be localized to a
precise intracellular compartment, cellular membrane
or organelle, or directed to the exterior of the cell [1].
In plants, the endomembrane system is a complex network of organelles specialized in the synthesis, transport, modification and secretion of proteins and other
macromolecules. This system is composed of several
functionally distinct membrane compartments: the
endoplasmic reticulum (ER), the Golgi apparatus
including the trans-Golgi network (TGN), secretory
vesicles, the vacuole and endosomes [2]. The mem-
branes of mitochondria and chloroplasts do not belong
to the endomembrane system [1–3]. Connection
between the various endosomal compartments is
achieved through tightly controlled, constant budding
and fusion of vesicle shuttles [4]. The endomembrane
system integrates several dynamic routes: the secretory
pathway (including biosynthesis and sorting) and the
endocytic pathway. As a result of their overlapping
routes and cargo distribution centres, it is difficult, if
not impractical, to separate these pathways from each
other. Proteins and other cargos are synthesized and
programmed to follow a certain sorting pathway to
reach their final destination. Although the dynamic
activities of endomembrane systems are highly
Abbreviations
AP, adaptor protein; Arf, ADP ribosylation factor; CCV, clathrin-coated vesicle; COP, coat protein complex; DV, dense vesicle;
ER, endoplasmic reticulum; LV, lytic vacuole; MPR, mannose 6-phosphate receptor; PSV, protein storage vacuole; RMR, receptor
membrane ring-H2; Sar, secretion-associated RAS-related protein; SNARE, soluble nethylmaleimide sensitive factor attachment protein
receptor; TGN, trans-Golgi network; TIP, tonoplast intrinsic protein; VSD, vacuolar sorting determinant; VSR, vacuolar sorting receptor.
FEBS Journal 280 (2013) 979–993 ª 2012 The Authors Journal compilation ª 2012 FEBS
979
L. Xiang et al.
Vacuolar protein sorting in plant cells
conserved among all eukaryotes, higher plants have
developed some unique mechanisms [5].
In plants, the secretory and biosynthetic trafficking
pathways are involved in a series of vital mechanisms,
such as gravitropism, autophagy, hormone transport,
cytokinesis and abiotic/biotic stress responses [6,7], as
well as in ion secretion by salt glands, nectar production, and the secretion of viscin, which is the elastic,
mucilaginous and sticky tissue that attaches falling parasitic mistletoe seeds to branches [8]. Over recent years,
remarkable progress has been achieved in the understanding of plant protein and membrane trafficking by
the use of different systems and approaches [4,9]. The
path followed by a protein depends on the interactions
between sorting motifs present in the protein and the
motif-recognizing machinery. Many of these motifs are
universally conserved among eukaryotes (yeast and
humans) [9]. However, sorting motif studies in plants
are still in their infancy compared to animal and yeast
systems. In plants, studies mainly address tissue-specific
and organelle-specific trafficking processes [9]. Generally, the protein secretory pathway begins in the ER,
passes through the Golgi complex, and finally reaches
the vacuole, other compartments or the cell surface
[4,9]. This review mainly focuses on the mechanisms
involved in protein sorting to the central vacuole as a
unique, multifunctional plant-specific organelle.
Sorting of proteins to plant vacuoles
Vacuolar proteins reach the different types of vacuoles
through a vesicle-mediated biosynthetic trafficking
pathway that includes the ER, the Golgi apparatus,
the TGN and the endosomes/prevacuoles (Fig. 1). In
plant cells, two different types of membrane receptors
are known: the vacuolar sorting receptor (VSR) family
[9] and the receptor membrane ring-H2 (RMR) family
[10].
The plant vacuole
The number and the size of plant vacuoles depend on
cell type and developmental stage. A single central
vacuole may occupy as much as 80% of the volume of
a cell. Plant vacuoles are essential multifunctional
organelles distinct from similar organelles in other
eukaryotes. They serve both physical and metabolic
functions, and are crucial to processes involved in the
cellular responses to environmental and biotic factors,
as well as to general cell homeostasis [11,12]. Vacuoles
typically store water, ions, secondary metabolites and
nutrients. Similar to animal lysosomes, they also act as
a repository for waste products, excess solutes and
980
A
B
Fig. 1. Model of protein sorting pathways to the plant vacuole. (A)
Protein sorting to the PSV. Proteins destined for the PSV initiate
their life in the ER and can be sorted to the PSV through Golgidependent or -independent pathways. In the Golgi-dependent
pathway, proteins are transported to the Golgi via COPII vesicles,
and then aggregate and become the cargo of DVs, being
transported into multivesicular bodies and then fusing into the PSV.
Notably, some storage proteins that need processing in the Golgi
reach the PSV via precursor-accumulating vesicles. In the Golgiindependent pathway, PSV residents are packed into precursoraccumulating vesicles and are transported to the PSV. MVB,
multivesicular body; PAC, precursor-accumulating vesicle; PV72/
RMR, vacuole sorting receptor. (B) Protein sorting to the LV.
Proteins destined for the LV initiate their life in the ER and can be
sorted to the LV through Golgi-dependent or -independent
pathways. In the Golgi-dependent pathway, the protein can be (a)
recognized by BP80/VSR and becoming the cargo of CCV, after
which it is transported to the prevacuolar compartment and, finally,
to the LV; or (b) transported via a putative AP3-mediated pathway
to the LV. In the Golgi-independent pathway, the LV residents are
transported through the ER bodies. A PSV (a-TIP) might be
transformed into an LV (c-TIP). Fusions of LVs or PSVs make up
the central vacuole. PVC, prevacuolar compartment; BP80/VSR,
vacuole sorting receptor.
toxic substances [13–16], and play key roles in (programmed) cell death [17–20].
Two types of vacuoles can be found in plant cells,
the protein storage vacuole (PSV) and the lytic
vacuole (LV) [21]. Typically, vacuolar storage proteins accumulate in PSVs. PSVs have higher pHs
and lower hydrolytic activities than LVs, and predominate in storage tissues (e.g. cotyledons and
endosperm in seeds, tubers), as well as in vegetative
tissues of adult plants (e.g. bark, leaves, pods)
[22,23]. Proteins stored in PSVs are mainly used as
nitrogen or carbon sources during seed germination
and plant development [24]. However, PSVs can also
contain large amounts of toxic proteins (e.g. lectins,
FEBS Journal 280 (2013) 979–993 ª 2012 The Authors Journal compilation ª 2012 FEBS
L. Xiang et al.
protease inhibitors and ribosome inactivating proteins), which can be considered as the result of a
cytosolic detoxification process or as a defence
against predators [25–27]. PSV proteins could be
processed through the action of vacuolar processing
enzymes or proteases [28–30]. By contrast, LVs are
usually found in vegetative tissues. They have an
acidic pH and contain an abundance of hydrolytic
enzymes [31,32]. LVs are used for storage and as a
depository of unwanted materials in plant cells. They
receive extracellular components via endocytosis and
phagocytosis, and intracellular material via autophagy, as well as via the biosynthetic trafficking
pathway and membrane-bound transport systems.
LVs modulate the degradation of a multitude of
macromolecules and other compounds. As such, they
are considered key regulators in cellular homeostasis
[33,34].
Tonoplast intrinsic proteins (TIPs) have been used
as intracellular markers for vacuolar biogenesis and
identity. The expression of TIPs, although tissue-specific, varies greatly throughout development. TIPs are
classified into five categories: a, b, c, d and e-TIPs
[35]. a and b-TIPs are seed-specific. c-TIPs associate
with the LV, whereas a-TIP and d-TIP associate with
the PSV [36,37]. e-TIPs are primarily found in root
and floral organs. Different TIPs can coexist in the
same cell, suggesting the presence of both LVs and
PSVs [33]. Evidence that LVs and PSVs can occur
together has been found in the root tip cells of barley
and pea seedlings [31,38], as well as in protoplasts of
barley aleurone and tobacco [32]. Interestingly, it was
reported that, during the germination of Arabidopsis
seeds, the LV is primarily embedded in the PSV and
then derives from it, instead of being generated
de novo [21,31,39]. Moreover, depending on physiological conditions, LVs can be transformed into PSVs and
vice versa [40–42]. In addition to PSVs and LVs,
a third type of vacuole has been suggested in Arabidopsis [43,44]. During leaf senescence, senescence-associated vacuoles, with a smaller size and containing
aggregates, are formed de novo [45], and are characterized by a higher cysteine-protease activity and a lower
pH than LVs [46].
The existence of two types of plant vacuoles with
distinct contents and functions implies that
separate trafficking pathways must exist for their
respective cargo [5], with a need for correct separation in the Golgi/TGN apparatus (Fig. 1). Furthermore, it can be hypothesized that the concurrent
existence of LVs and PSVs provides plants with
extra flexibilities to deal with changing environmental
conditions.
Vacuolar protein sorting in plant cells
Sorting of vacuolar proteins is initiated in the ER
The initiation of vacuolar/lysosomal protein sorting in
the ER is a very conserved mechanism in yeast,
animals and plants [5,9]. The ER represents the first
compartment of the secretory system [47]. The ER
membrane connects to the nuclear envelope, and forms
a wide network of thin tubules and cisternae in the
cortical and inner parts of the cell [47]. Both transmembrane proteins and soluble, secreted proteins contain an ER signal sequence including a hydrophobic
20–25 amino-acid segment. As a result of its hydrophobic nature, the signal sequence is inserted into the
ER membrane. The difference between the secreted
and transmembrane proteins is that the hydrophobic
sequence is removed by the ER signal peptidases from
the secreted proteins, although not from the transmembrane proteins [48,49]. Based on the model of
Singer and Nicolson [50], integral membrane proteins
can be classified as: (a) type I transmembrane proteins
containing a single transmembrane domain with an
Nout/Cin orientation (‘in’ means cytoplasmic side, ‘out’
means lumen); (b) type II transmembrane proteins
containing a single transmembrane domain with an
Nin/Cout orientation; (c) type III membrane proteins
(multiple transmembrane domains in a single polypeptide chain); and (d) type IV membrane proteins (multiple transmembrane domains reside on a single or
multiple individual polypeptide chain).
The ER is also an important check point of correct
protein folding and assembly, known as stringent quality control [51]. Only properly folded and assembled
proteins are allowed to exit the ER. Misfolded proteins are recognized by molecular chaperones (e.g. BiP,
calnexin) and retained in the lumen of the ER in an
attempt to re-fold them to their correct, native structure [52–54]. Persistent misfolded proteins are transferred to the cytosol and degraded by the proteasome
system [55,56]. Proteins that have erroneously reached
the Golgi can also return to the ER when ER retention signals are present [57].
Vesicular trafficking
Plant cells, similar to all eukaryotes, are structurally
and metabolically subdivided into different compartments, with communication between organelles being
accomplished mainly by vesicular trafficking. This is a
highly-regulated and directional/targeted process. In
general, the vesicle trafficking process involves budding, vesicle release, targeted transport, tether, and
membrane recognition and fusion [58]. Vesicle trafficking is also involved in secretion into the apoplast and,
FEBS Journal 280 (2013) 979–993 ª 2012 The Authors Journal compilation ª 2012 FEBS
981
L. Xiang et al.
Vacuolar protein sorting in plant cells
during endocytosis, recycling proteins from the plasma
membrane to the endosome, the TGN and the lysosome/vacuole [5,47]. In all eukaryotes, clathrin-coated
vesicle (CCV), caveolin, coat protein complex I (COPI)
and coat protein complex II (COPII) vesicles carry out
these functions and have an ubiquitous presence and
budding machineries.
Vesicle formation is not a default, passive event, but
instead, requires a specific driving force to carry out a
series of highly-regulated events including recognition
and binding between the receptor at the donor membrane and an activated GTP-ADP ribosylation factor
(Arf) complexed with the secretion-associated RASrelated protein (Sar)1 complex, recruiting coatomer,
membrane distortion and dissociation under the assistance of fatty acyl CoA, and the formation and release
of a vesicle. Similar to animals and yeast, in plants,
most of the Sar/Arf1 GTPases are well conserved. The
Arf1 family is necessary for COPI vesicle and CCV
formation, whereas the Sar1 family is mainly involved
in COPII vesicle formation [59,60]. After formation,
the vesicle is released and travels towards the target
compartment assisted by actin filaments, where it disassembles with the help of a cytosolic Hsc70 chaperone. After the uncoating process [61–63], specific
vesicle soluble nethylmaleimide sensitive factor attachment protein receptor (SNARE) proteins, exposed on
the vesicle’s membrane, bind to cognate targetSNARE proteins complexed with synaptosomal-associated protein 25. Next, nethylmaleimide sensitive factor
and soluble nethylmaleimide sensitive factor attachment proteins bind to this complex, which dissociates
after vesicle fusion. Sec1p and Rab proteins serve as
effectors for SNARE complex regulation during vesicle
targeting and fusion [62–64].
Trafficking between the ER and the Golgi apparatus
Although the sorting of plant vacuolar proteins commences at the ER [64], the Golgi apparatus is the
major sorting station in the plant cell [65]. The ER
and Golgi communicate with each other via a highlyregulated traffic system. Transfer from the ER to the
Golgi apparatus is the first step in protein sorting via
the biosynthetic trafficking pathway. This is mediated
by COPII vesicles. The retrograde transport from the
Golgi to the ER is accomplished via COPI vesicles,
which are morphologically and biochemically different
from the COPII vesicles of the retrograde system
[66,67].
The COPII vesicles mediate the anterograde traffic
export protein from ER the to the Golgi apparatus in
eukaryotic cells [68,69]. COPII is composed of three
982
components: Sar1, Sec23/24 and Sec13/31. After budding off from the ER, COPII vesicles can either
directly fuse with cis-Golgi, or first fuse with each
other and then to the cis-Golgi [68,70,71].
The role of COPI vesicles for retrograde traffic from
the Golgi to the ER or within the Golgi apparatus
from the trans- towards the cis-Golgi in plants was
first demonstrated in transgenic tobacco [72]. COPI
consists of coatomer (F-COP and B-COP subunit) and
Arf G-protein. Two classes can be discerned: COPIa
vesicles are derived from cis-cisternae, and COPIb vesicles are derived from medial and trans-cisternae [73].
Different classes of COPI vesicles are caused by multiple isoforms of COP subunits [73]. The distribution of
proteins between ER and Golgi is maintained by the
balanced cooperation of COPI and COPII transport
routes. Inhibition of COPI function results in impaired
trafficking between the Golgi and the ER and disruption of the ER export sites [72,74,75].
For exit of proteins from the ER, different types of
motifs have been identified that are recognized by
COPII. Di-acidic (e.g. DXE/EXE), di-basic (e.g.
RKXRK) and di-aromatic motifs in the cytosolic tail
of transmembrane proteins were reported to be important for the export of proteins from the ER in yeast
and animals [68]. The first evidence for a di-acidic
motif (DAE) in protein export from the ER in plants
was obtained for a sugar transporter in tobacco [76].
Next, Schoberer et al. [77] demonstrated the importance of a di-basic motif (RKR) in tobacco as well.
Retrograde Golgi-ER transport of soluble proteins
is achieved by C-terminal H/KDEL motifs that are
recognized by the receptor ER retention defective 2
protein embedded in the membrane. Thus, H/KDEL
motifs are considered to be responsible for the retention of soluble proteins in the ER lumen, and are
named ER retention signals. H/KDEL containing proteins never undergo the typical modifications observed
in Golgi-derived enzymes [78,79].
Intra-Golgi and post-Golgi transport
The plant Golgi apparatus appears to be more complicated than its animal counterpart. It is divided into
functionally independent individual Golgi stacks and
has a polarized structure, whereas the animal Golgi
apparatus is perinuclear and stationary [75]. After
receiving newly-synthesized proteins from the ER, the
Golgi apparatus performs covalent modifications, and
then further distributes the proteins to various final
destinations [80].The cis-Golgi constitutes the entrance
to the apparatus, whereas vesicles leave at the transGolgi to reach their final destination [65,81]. The
FEBS Journal 280 (2013) 979–993 ª 2012 The Authors Journal compilation ª 2012 FEBS
L. Xiang et al.
Golgi is also implicated in protein trafficking to nonsecretory organelles such as peroxisomes and chloroplasts. The Golgi apparatus plays an important role
in post-translational modification mainly through
transmembrane processing enzymes. Proteins enter the
cis-Golgi, move through the med-Golgi and reach the
trans-Golgi where the modification process is completed, such as glycosylation, sulfation and phosphorylation [82]. Two models of intra-Golgi transport have
been proposed: the vesicle shuttle and the cisternal
maturation models. Notably, multiple Golgi-independent protein transport pathways exist for delivering
cargo molecules from the ER to a variety of destinations, such as celery mannitol dehydrogenase delivery
to the extracellular space [83] and barley aspartic protease transport to the vacuole [84].
Post-Golgi vesicle transport: the CCV
The CCVs were the first type of coated vesicles to be
described in eukaryotes. Typically CCVs are 50–
100 nm in diameter, formed at the plasma membrane
and TGN/endosomes and are involved in the trafficking of protein cargo between these organelles [85].
There is evidence for their formation at the lysosomes
of animals [86] and the vacuoles of yeast [87], yet there
are no confirmed reports of CCV formation in plant
vacuoles. They are also implicated to play a role in
other processes such as defence responses and cytokinesis. The formation of a clathrin coat requires various
adaptor proteins (APs), clathrin and dynamin (a GTPbinding protein, Arf). The clathrin unit is a threelimbed shaped triskeleton, each limb containing one
clathrin heavy chain and one light chain [88]. Two
other proteins, amphiphysin and synaptojanin, are
involved in CCV formation as well. The clathrin coat
can be depolymerized by cytosolic Hsc70, and re-used
[89–91]. A distinctive characteristic of plant CCVs is
their larger size. Capacitance measurements of endocytic events during fluid phase endocytosis in tobacco
BY-2 protoplasts estimated the size of vesicles to be a
mean of 133 nm [92]. These estimates are similar to
those obtained by Gall et al. [93] in turgid guard cells.
By contrast, estimates of CCVs in nonplant systems
appear to be between 70 and 100 nm [94].
Vacuolar sorting machinery
Plant vacuolar sorting determinants (VSDs)
VSDs are necessary for correct post-Golgi sorting to
the vacuole. Plant cells contain three different categories of VSDs: (a) sequence-specific VSDs; (b) C-terminal VSDs; and (c) protein structure-dependent VSDs
Vacuolar protein sorting in plant cells
[80,95]. Without these motifs, vacuolar proteins follow
the default pathway and are secreted to the surface of
the cell, whereas their introduction into a secreted protein could redirect it to the vacuole [96]. In general,
N-terminal sequence-specific VSDs and C-terminal
VSDs are removed during protein maturation after vacuolar sorting by the action of vacuolar proteases [97].
Sequence-specific VSDs are generally considered to
be recognized by VSRs for sorting to the LV, as in the
case of barley aleurain and sporamin [98–101]. Functional sequence-specific VSDs (NPIXL/NPIR) were
also described in storage protein sorting to the PSV,
such as castor 2S albumin and ricin [102–104].
Sequence-specific VSDs function independently of their
molecular position, although they are most often situated at the N-terminus of a protein. For example,
sporamin type sequence-specific VSDs are still able to
direct protein to the vacuole after translocation from
the N-terminus to the C-terminus [99,105]. There are
some examples of C-terminal and even internal
sequence-specific VSDs [106].
In plants, C-terminal VSDs were first discovered in
barley lectin and tobacco chitinase [107,108]. The minimal length is four amino acids [103]. Many random
C-terminal peptides are sufficient to target a reporter
protein to the vacuole. For example, the C-terminal
VSD of tobacco chitinase A (GLLVDTM), and the
FAEAI and LVAE motifs of barley lectin, are necessary and sufficient for vacuolar targeting [107–109].
Moreover, the IAGF motif from 2S albumin of Passifloraceae, the PLSSILRAFY motif of the b-conglycinin a unit of soybean and the KISIA motif from the
11S albumin of Amaranthus are all functional C-terminal VSDs [106,110,111]. C-terminal VSDs must strictly
localize to the C-terminal part of the protein. Moreover, the introduction of C-terminal glycosylation sites
or addition of extra alanine stretches at the C-terminus
led to cell surface secretion [112,113]. Some proteins
even combine a sequence-specific VSD and a C-terminal VSD for dual targeting to the PSV matrix and to
globoids [114]. Importantly, random C-terminal VSDs
appear to be rather unique to plants. Despite more
extensive research on animal systems, only a few cases
have been reported in animals [115], where tyrosine
motifs (YXXΦ) are more commonly used [116,117].
The physical and structural VSDs are based on protein structure, and can be subdivided in two types. The
first type may be composed of multiple internal
domains forming a higher-order structure to function
as a VSD. This is the case for the 11S globulin legumin from field bean. The second type is formed by the
aggregation of seed storage proteins, presumably
occurring in the Golgi apparatus. Proproteins are
FEBS Journal 280 (2013) 979–993 ª 2012 The Authors Journal compilation ª 2012 FEBS
983
L. Xiang et al.
Vacuolar protein sorting in plant cells
often more hydrophobic than their mature counterparts and therefore they form aggregates. This nonreceptor-mediated sorting mechanism was reported for
seed storage proteins reaching the PSV through dense
vesicles (DVs), which are unique vesicles only occurring in plants [106,113,118,119].
VSRs
In 1994, the first VSR was identified from a pea cotyledon CCV preparation. The protein was termed BP80
(binding protein 80 kDa) by its ability to bind in vitro
the VSD of barley aleurain [120]. VSRs are type I
membrane proteins with a cytosolic motif and a large
lumenal domain. They are not related to TGN sorting
receptors such as the mannose 6-phosphate receptor
(MPR) in animals or the vacuolar carboxypeptidase
sorting receptor VPS10 in yeast [121,122]. VSRs generally recognize NPIRL-(like) consensus motifs in cargo
proteins (mostly present at the N-terminus in cargo),
whereas, in turn, VSRs themselves are recognized by
AP1 via its YMPL consensus motif at the C-terminus.
VSRs are generally considered to mediate protein sorting to LV, as supported by several pieces of evidence.
First, VSRs recognize and bind the sequence-specific
VSDs present in LV proteins, such as barley aleurain
and sporamin [123]. Second, VSRs contain a tyrosine
motif for interaction with the AP1 complex l1 subunit
and subsequent packing into the CCV [5,124]. Third,
Arabidopsis thaliana vacuolar sorting receptor 1,
a BP80 homologue from Arabidopsis, interacts with
AtEpsinR1, with its animal homologue being involved
in CCV-mediated trafficking to lysosomes [125,126].
Fourth, the A. thaliana vacuolar sorting receptor 1
C-terminal cytosolic tail interacts with AtVPS35, a
prevacuolar compartment localized retromer from
Arabidopsis [127]. Fifth, despite the fact that VSRcargo ligand interaction might be initiated in the ER
[64], VSRs are accumulating to a high extent in the
prevacuolar compartment and to a lower extent in the
TGN [128]. Finally, the pH-dependent ligand binding
indicates that the receptor-cargo complex needs to end
up in an acidic environment to release its cargo [129].
However, several studies also report interactions
between VSRs and VSDs of storage proteins such as
2S albumins in castor bean [10,102]. PV72, a pumpkin
homologue of VSR, was identified in the precursoraccumulating compartments that are proposed as
intermediates in the transport of storage proteins to
the PSV [130,131]. Similar results have been found in
sunflower [132] and castor bean [112]. By contrast to
the vacuolar sorting receptor BP80, ligand binding to
PV72 is calcium-dependent because it is released at a
984
low calcium concentration. Additionally, A. thaliana
vacuolar sorting receptor 1 (also termed AtELP1) was
shown to play a role in sorting storage proteins in
seeds, which also shows calcium-dependence [133].
These results indicate that different isoforms may be
involved in different sorting pathways. The recent finding that VSRs could be localized at the plasma membrane suggested an additional role for VSR proteins in
mediating protein transport towards the plasma membrane and endocytosis in germinating pollen tubes of
lily and tobacco [122].
The RMR protein family
The RMR protein family RingH2 was originally discovered as a result of their homology to protease-associated domains in VSRs, indicating their role in
binding vacuolar proteins [10]. In vitro experiments
showed the capability of RMR to bind to the C-terminal VSD of barley lectin, bean phaseolin and tobacco
chitinase, which are then transported to the PSV
[134,135]. The RMRs are type I transmembrane proteins containing a typical N-terminal signal peptide,
followed by a protease-associated domain and a single
transmembrane domain [136]. By contrast to the short
cytoplasmic tail of VSRs, plant RMRs contain a long
cytoplasmic tail with a typical C3H2C3 RING-H2
domain [10]. One isoform of Arabidopsis, AtRMR1,
has been mainly localized in the late Golgi apparatus,
DVs and in the PSV of Arabidopsis embryos by the
use of immunogold electron microscopy [137].
AtRMR2 was localized in the PSV [138], whereas
other RMRs were also found in the PSV of tomatoes
[13] and in members of the Brassicaceae [139]. These
findings are compatible with the hypothesis of its role
as a receptor in protein sorting to the PSV [122].
Recently, it was demonstrated that rice RMR1 associated with an intermediate vacuolar-like compartment
related to the PSV [140].
AP complexes
AP complexes are heterotetramers mediating the formation of transport vesicles, as well as cargo sorting in
all eukaryotes. Most of the research on AP complexes
has been devoted to animals and yeast. According to
Hirst et al. [141], five distinct AP complexes (AP1–
AP5) have been identified in eukaryotes to date. AP
complexes are composed of two large subunits (termed
a/b1, a/b2, d/b2, e/b4 and ξ/b5, respectively), a medium subunit (l1–l5) and a small subunit (r1–r5) [141
–144]. The c/b1 and a/b2 subunits of AP1 and AP2
bind clathrin via clathrin-binding sites within their
FEBS Journal 280 (2013) 979–993 ª 2012 The Authors Journal compilation ª 2012 FEBS
L. Xiang et al.
hinge domains [145]. Each AP complex operates in distinct organelle localization and performs similar functions. The AP1 complex is involved in CCV formation
at the TGN and endosomes, mediating the trafficking
between these organelles [146,147]. The AP2 complex
contributes to the formation of CCV from the plasma
membrane and facilitates clathrin-mediated endocytosis [148,149]. The AP3 complex is involved in the formation of vesicles from TGN/endosomes, and
mediates transport to lysosomes/vacuoles [147,150].
The clathrin binding of AP3 is under debate. In Arabidopsis, AP3 subunit loss-of-function mutants implicated AP3 in biogenesis and function of the plant LV
[151–153]. The AP4 complex was recently defined as a
mediator of the transport of the amyloid precursor
protein from the TGN to the endosome [154]. It was
suggested to be involved in vesicle formation with or
without clathrin [155,156]. The AP5 complex does not
associate with clathrin, localizes in late endosomal
compartments, and mediates endosomal sorting [144].
In the biosynthetic and endocytic trafficking pathways, AP complexes selectively recognize sorting signals [145]. A number of such sorting signals have been
identified in the last decade, such as tyrosine signals
(NPXY and YXXФ signals, where X could be any
amino acid and Ф is a bulky hydrophobic amino acid),
and dileucine signals ([DE]XXXXL[LI] and DXXLL
consensus motifs) [147]. AP complexes are known to
interact with tyrosine-based sorting signals via their l
subunits, although the AP subunits that recognize
dileucine-based sorting signals remain unidentified.
There is evidence indicating that AP1 binds via its c
and r1 subunits [157], whereas AP3 binds via its b
unit [145,158].
Protein sorting to the vacuole
Protein sorting to the PSV
Storage proteins are transported to the PSV via Golgidependent or -independent pathways depending on the
cargo protein and plant developmental stage [4,159].
Unlike LVs, the trafficking of storage proteins from
the Golgi apparatus into the PSV is mediated by DVs
rather than by CCVs [160,161]. DVs are small, uniform
vesicles (150–200 nm in diameter) containing intrinsic
membrane proteins destined for the PSV, and are characterized by their high density electron-opaque lumenal
contents [113]. They were first discovered in common
bean [160], and later in other plant species, such as
wheat [162], pea [163] and Arabidopsis [137]. Within the
cis-Golgi, the accumulation and condensation of storage
proteins initiates the formation of DVs. Subsequently,
these discrete small vesicles are transferred to the TGN
Vacuolar protein sorting in plant cells
concomitant with increased density and, finally, they are
released from the TGN [80,137]. Mature DVs are not
protein coated; they can directly fuse with the PSV or
first with multivesicular bodies [13,161,164,165]. Multivesicular bodies contain multiple internal vesicles, are
present in all eukaryotes, and are involved in various
post-Golgi processes of the biosynthetic trafficking
pathway. DVs fuse into the multivesicular bodies where
they discharge their contents [166]. Multivesicular
bodies are then received by the PSV together with their
cargos. Therefore, the Golgi-dependent PSV trafficking
pathway could be defined as an ER?Golgi?DV?
(multivesicular bodies)?PSV pathway (Fig. 1A). Protein transport to the PSV mainly occurs through aggregation sorting, although receptor-mediated sorting
might play a role as well [132]. In this case, the involved
VSRs are BP80 homologues (such as PV72, AtELP1)
and RMRs [80,112,113,167,168]. Many proteins have
been reported that sort to the PSV via DVs, such as legumin, vicilin and sucrose-binding-protein homologue
[132,169].
Transport of storage proteins to the PSV can also
take an alternative route from the ER bypassing the
Golgi, as shown in Fig. 1A. Globulins, the major vacuolar storage proteins in pumpkins, were suggested to
reach the PSV via precursor-accumulating compartments, which are much larger (diameter of 200–400 nm)
than DVs, and reach the PSV directly from the ER
[130,170]. Similar results have been obtained for cysteine
proteinases [171,172]. Precursor-accumulating compartments contain unglycosylated precursors of storage
proteins, and mediate aggregation sorting. Precursoraccumulating compartments have been found in pumpkin, castor beans and in wheat [130,173,174]. Although
directly generated from the ER, precursor-accumulating
compartments can accept glycosylated proteins derived
from the Golgi during their transport to the PSV
[112,130]. The content of precursor-accumulating compartments is incorporated in the lumen of the PSV. The
incorporation follows one of two models: (a) fusion
between precursor-accumulating compartments and
PSV occurs through autophagy [175,176] or (b) by
direct membrane fusion [177].
Protein sorting to the LV
Different pathways for post-Golgi sorting of proteins to
lysosomes/vacuoles have been described for yeast and
animals. The pathway through CCVs appears to be conserved among all eukaryotes (plants, yeast, animals).
Inside the TGN, specific sorting signals are recognized
by TGN membrane localized receptors, recruited into
CCVs and transported into LVs/lysosomes [165,178]. In
FEBS Journal 280 (2013) 979–993 ª 2012 The Authors Journal compilation ª 2012 FEBS
985
L. Xiang et al.
Vacuolar protein sorting in plant cells
animal cells, the sorting of acid hydrolases to the lysosome is facilitated by the MPR [179]. MPR-ligand complexes are recruited into CCVs at the TGN. This
process is mediated by Golgi-localized, c adaptin earcontaining, Arf-binding proteins and by the AP1 complex through interactions with MPRs tyrosine (YXXФ)
and dileucine (LL) motifs at the cytosolic tail [179,180].
In yeast, the sorting and delivery to the LV is very similar to the MPR pathway of animal cells [181,182]. This
mechanism is assumed to be used for trafficking to plant
LVs as well, although LV proteins interact with VSRs,
showing no homology to MPRs [85]. Plant VSRs recognize sequence-specific VSDs (e.g. NPIRL-like consensus
motifs) in LV targeted proteins, such as barley aleurain
[183,184]. VSRs then interact with AP1 through a tyrosine-based sorting motif (e.g. YMPL) instead of through
a dileucine motif as observed in yeast and animals [124].
CCVs, containing cargo-VSR, then bud from the TGN,
and discharge their contents after fusion into the prevacuolar compartment [163,166]. As a result of the lower
pH of the prevacuolar compartment, ligands dissociate
from their receptor, and the receptor is subsequently
recycled back to the Golgi apparatus [185–187]. Importantly, an MPR-independent and a VPS10-independent
lysosome sorting pathway were found in animal cells
and yeast, respectively [188,189]. Recent studies on the
sorting of tonoplast transporters in Arabidopsis mesophyll protoplasts suggest a similar route in plants
(Fig. 1B) [190]. AP3, but not AP1, appears to fulfill a
central role in this pathway. In animals, AP3 can recognize both dileucine and tyrosine motifs, whereas, in
yeast, only dileucine signals can be recognized [145,191].
Recent reports suggest that AP3 subunits are involved
in the biogenesis, morphology and function of the
prevacuolar compartment and vacuoles in plants [151–
153].
Remarkably, and uniquely in plants, LV resident
proteins can be transported directly from the ER to
the LV by means of ER bodies as intermediate compartments, bypassing the Golgi apparatus, as shown in
Fig. 1B [170]. Thus, one of the emerging differences
that appears to distinguish plants from other eukaryotes is the plasticity of the ER to form protein-, oil- or
rubber-containing subcellular structures best termed
ER bodies [192], which either stably accumulate or are
transported to the LV. The ER bodies are in most
instances spherical, < 1 lm in diameter, and consist of
a dense core of a self-assembling or aggregating protein, oil or rubber, and a membrane of ER origin
[193]. However, there is some evidence for nonconventional ER trafficking bypassing the Golgi to the lysosome in animal cells [194]. It was proposed that ER
bodies in plants can follow a similar path, bypassing
986
the Golgi and directly fusing with LV, as observed
under stress conditions [195,196].
Conclusions and perspectives
Recent advances in our understanding of the processes
involved in the sorting of proteins to the vacuole(s) in
plant cells suggest that there are relatively highly-conserved processes among eukaryotes. Most differences
are related to the uniqueness of the plant vacuole as a
storage compartment, as opposed to the animal lysosome and the yeast vacuole, which function predominantly as hydrolytic compartments. Another distinctive
feature is the apparent duplicity and alternative pathways for proteins to reach the lytic and protein storage
vacuolar lumen or tonoplast. Furthermore, the variety
of chemical substances stored in the vacuole (e.g. protein bodies, resins, gums, latex, sugars, etc.) imposes the
acquisition of redundant transport pathways to the vacuole. One aspect of the vesicle-mediated delivery system
to the vacuole that awaits clarification is how the vacuoles compensate for the increasing uptake of fluids and
added membrane during the vesicle fusion process. At
present, there are no indications as to how homeostasis
is maintained, although, in yeast, the formation of retrograde CCV has been observed. The alternative postGolgi, AP3-mediated route has been well described in
yeast and animals, although further experimental work
is required to determine whether this route is also fully
active in plants. Furthermore, the regulatory mechanisms of the AP3-mediated and Golgi-independent
routes, as well as the cargos, receptors and possible
budding factors involved, still remain elusive and
require further exploration. The use of fluorescent
probes, transgenic plants and new imaging techniques
will likely provide us with a clearer understanding in
the near future.
Acknowledgements
Li Xiang and Wim Van den Ende are supported by
grants from FWO Vlaanderen.
References
1 Vitale A & Galili G (2001) The endomembrane system
and the problem of protein sorting. Plant Physiol 125,
115–118.
2 Frigerio L & Hawes C (2008) The endomembrane
system: a green perspective. Traffic 9, 1563.
3 Dacks JB, Peden AA & Field MC (2009) Evolution
of specificity in the eukaryotic endomembrane system.
J Biochem Cell Biol 41, 330–340.
FEBS Journal 280 (2013) 979–993 ª 2012 The Authors Journal compilation ª 2012 FEBS
L. Xiang et al.
4 Rojo E & Denecke J (2008) What is moving in
the secretory pathway of plants? Plant Physiol 147,
1493–1503.
5 J€
urgens G (2004) Membrane trafficking in plants. Annu
Rev Cell Dev Biol 20, 481–504.
6 Carter C, Pan S, Zouhar J, Avila EL, Girke T &
Raikhel NV (2004) The vegetative vacuole proteome of
Arabidopsis thaliana reveals predicted and unpredicted
proteins. Plant Cell 16, 3285–3303.
7 Surpin M & Raikhel N (2004) Traffic jams affect plant
development and signal transduction. Nat Rev Mol
Cell Biol 5, 100–109.
8 Echeverrıa E (2000) Vesicle-mediated solute transport
between the vacuole and the plasma membrane. Plant
Physiol 123, 1217–1226.
9 De Marcos Lousa C, Gerschlick DC & Denecke J
(2012) Mechanisms and concepts paving the way
towards a complete transport cycle of plant
vacuolar sorting receptors. Plant Cell 24,
1714–1732.
10 Cao X, Rogers SW, Butler J, Beevers L & Rogers JC
(2000) Structural requirements for ligand binding by a
probable plant vacuolar sorting receptor. Plant Cell
12, 493–506.
11 Marty F (1999) Plant vacuoles. Plant Cell 11, 587–600.
12 Martinoia E, Maeshima M & Neuhaus HE (2007)
Vacuolar transporters and their essential role in plant
metabolism. J Exp Bot 58, 83–102.
13 Jiang L, Phillips TE, Rogers SW & Rogers JC (2000)
Biogenesis of the protein storage vacuole crystalloid.
J Cell Biol 150, 755–770.
14 Bethke PC & Jones RL (2000) Vacuoles and
prevacuolar compartments. Curr Opin Plant Biol 3,
469–475.
15 Martinoia E, Massonneau A & Frangne N (2000)
Transport processes of solutes across the vacuolar
membrane of higher plants. Plant Cell Physiol 41,
1175–1186.
16 Hatsugai N, Kuroyanagi M, Yamada K, Meshi T,
Tsuda S, Kondo M, Nishimura M & Hara-Nishimura
I (2004) A plant vacuolar protease, VPE, mediates
virus-induced hypersensitive cell death. Science 305,
855–858.
17 Hara-Nishimura I & Hatsugai N (2011) The role of
vacuole in plant cell death. Cell Death Differ 18,
1298–1304.
18 Gadjev I, Stone JM & Gechev TS (2008) Programmed
cell death in plants: new insights into redox regulation
and the role of hydrogen peroxide. Int Rev Cell Mol
Biol 270, 87–144.
19 Guicciardi ME, Leist M & Gores GJ (2004)
Lysosomes in cell death. Oncogene 23, 2881–2890.
20 Xiao H, Chen D, Fang Z, Xu J, Sun X, Song S,
Liu J & Yang C (2009) Lysosome biogenesis
mediated by VPS-18 affects apoptotic cell
Vacuolar protein sorting in plant cells
21
22
23
24
25
26
27
28
29
30
31
32
33
FEBS Journal 280 (2013) 979–993 ª 2012 The Authors Journal compilation ª 2012 FEBS
degradation in Caenorhabditis elegans. Mol Biol Cell
20, 21–32.
Bolte S, Lanquar V, Soler M-N, Beebo A, SatiatJeunema^ıtre B, Bouhidel K & Thomine S (2011)
Distinct lytic vacuolar compartments are embedded
inside the protein storage vacuole of dry and
germinating Arabidopsis thaliana seeds. Plant Cell
Physiol 52, 1142–1152.
M€
untz K (1998) Deposition of storage proteins. Plant
Mol Biol 38, 77–99.
Zouhar J, Mu~
noz A & Rojo E (2010) Functional
specialization within the vacuolar sorting receptor
family: VSR1, VSR3 and VSR4 sort vacuolar storage
cargo in seeds and vegetative tissues. Plant J 64,
577–588.
Wang J, Li Y, Lo SW, Hillmer S, Sun SSM, Robinson
DG & Jiang L (2007) Protein mobilization in
germinating mung bean seeds involves vacuolar sorting
receptors and multivesicular bodies. Plant Physiol 143,
1628–1639.
C^andido EDS, Pinto MFS, Pelegrini PB, Lima TB,
Silva ON, Pogue R, Grossi-de-Sa MF & Franco OL
(2011) Plant storage proteins with antimicrobial
activity: novel insights into plant defense mechanisms.
FASEB J 25, 3290–3305.
Jørgensen M, Stensballe A & Welinder KG (2011)
Extensive post-translational processing of potato tuber
storage proteins and vacuolar targeting. FEBS J 278,
4070–4087.
Lord JM & Spooner RA (2011) Ricin trafficking in
plant and mammalian cells. Toxins 3, 787–801.
Otegui MS, Herder R, Schulze J, Jung R & Staehelind
LA (2006) The proteolytic processing of seed storage
proteins in Arabidopsis embryo cells starts in the
multivesicular bodies. Plant Cell 18, 2567–2581.
Yamada K, Shimada T, Nishimura M & HaraNishimura I (2005) A VPE family supporting various
vacuolar functions in plants. Plysiol Plant 123, 369–375.
Nakaune S, Yamada K, Kondo M, Kato T, Tabata S,
Nishimura M & Hara-Nishimura I (2005) A vacuolar
processing enzyme, deltaVPE, is involved in seed coat
formation at the early stage of seed development.
Plant Cell 17, 876–887.
Olbrich A, Hillmer S, Hinz G, Oliviusson P &
Robinson DG (2007) Newly formed vacuoles in root
meristems of barley and pea seedlings have
characteristics of both protein storage and lytic
vacuoles. Plant Physiol 145, 1383–1394.
Park M, Kim SJ, Vitale A & Hwang I (2004)
Identification of the protein storage vacuole and
protein targeting to the vacuole in leaf cells of three
plant species. Plant Physiol 134, 625–639.
Frigerio L, Hinz G & Robinson DG (2008) Multiple
vacuoles in plant cells: rule or exception? Traffic 10,
1564–1570.
987
L. Xiang et al.
Vacuolar protein sorting in plant cells
34 Rogers JC (2008) Multiple vacuoles in plant cells
– response. Plant Physiol 146, 1024–1025.
35 Maurel C (2007) Plant aquaporins: novel functions
and regulation properties. FEBS Lett 581, 2227–2236.
36 Gattolin S, Sorieul M & Frigerio L (2011) Mapping of
tonoplast intrinsic proteins in maturing and
germinating Arabidopsis seeds reveals dual localization
of embryonic TIPs to the tonoplast and plasma
membrane. Mol Plant 4, 180–189.
37 Gattolin S, Sorieul M, Hunter PR, Khonsari RH &
Frigerio L (2009) In vivo imaging of the tonoplast
intrinsic protein family in Arabidopsis roots. BMC
Plant Biol 9, 133.
38 Paris N, Stanley CM, Jones RL & Rogers JC (1996)
Plant cells contain two functionally distinct vacuolar
compartments. Cell 85, 563–572.
39 Zheng H & Staehelin LA (2011) Protein storage
vacuoles are transformed into lytic vacuoles in root
meristematic cells of germinating seedlings by multiple,
cell type-specific mechanisms. Plant Physiol 155,
2023–2035.
40 Swanson S & Jones R (1996) Gibberellic acid induces
vacuolar acidification in barley aleurone. Plant Cell 8,
2211–2221.
41 Herman E & Larkins B (1999) Protein storage bodies
and vacuoles. Plant Cell 11, 601–614.
42 Murphy KA, Kuhle RA, Fischer AM, Anterola AM &
Grimes HD (2005) The functional status of paraveinal
mesophyll vacuoles changes in response to altered
metabolic conditions in soybean leaves. Funct Plant
Biol 32, 335.
43 Hunter PR, Craddock CP, Di Benedetto S, Roberts
LM & Frigerio L (2007) Fluorescent reporter proteins
for the tonoplast and the vacuolar lumen identify a
single vacuolar compartment in Arabidopsis cells.
Plant Physiol 145, 1371–1382.
44 Di Sansebastiano GP, Paris N, Marc-Martin S &
Neuhaus JM (2001) Regeneration of a lytic
central vacuole and of neutral peripheral vacuoles
can be visualized by green fluorescent proteins
targeted to either type of vacuole. Plant Physiol 126,
78–86.
45 Martınez DE, Costa ML, Gomez FM, Otegui MS &
Guiamet JJ (2008) ‘Senescence-associated vacuoles’ are
involved in the degradation of chloroplast proteins in
tobacco leaves. Plant J 56, 196–206.
46 Otegui MS, Noh Y-S, Martınez DE, Vila Petroff MG,
Staehelin LA, Amasino RM & Guiamet JJ (2005)
Senescence-associated vacuoles with intense proteolytic
activity develop in leaves of Arabidopsis and soybean.
Plant J 41, 831–844.
47 Bassham DC, Brandizzi F, Otegui MS & Sanderfoot
AA (2008) The secretory system of Arabidopsis.
Arabidopsis Book 65, 1.
988
48 Shan S-O, Schmid SL & Zhang X (2009) Signal
recognition particle (SRP) and SRP receptor: a new
paradigm for multistate regulatory GTPases.
Biochemistry 48, 6696–6704.
49 Johnson AE & Van Waes MA (1999) The translocon:
a dynamic gateway at the ER membrane. Annu Rev
Cell Dev Biol 15, 799–842.
50 Singer SJ & Nicolson GL (1972) The fluid mosaic
model of the structure of cell membranes. Science 175,
720–731.
51 Claessen JHL, Kundrat L & Ploegh HL (2012) Protein
quality control in the ER: balancing the ubiquitin
checkbook. Trends Cell Biol 22, 22–32.
52 Trombetta ES & Parodi AJ (2003) Quality control and
protein polding in the secretory pathway. Annu Rev
Cell Dev Biol 19, 649–676.
53 Liu J-X & Howell SH (2010) Endoplasmic reticulum
protein quality control and its relationship to
environmental stress responses in plants. Plant Cell 22,
2930–2942.
54 Kleizen B & Braakman I (2004) Protein folding and
quality control in the endoplasmic reticulum. Curr
Opin Cell Biol 16, 343–349.
55 Ellgaard L & Helenius A (2003) Quality control in
the endoplasmic reticulum. Nat Rev Mol Cell Biol 4,
181–191.
56 Hebert DN & Molinari M (2007) In and out of the
ER: protein folding, quality control, degradation, and
related human diseases. Physiol Rev 87, 1377–1408.
57 Pimpl P, Taylor JP, Snowden C, Hillmer S, Robinson
DG & Denecke J (2006) Golgi-mediated vacuolar
sorting of the endoplasmic reticulum chaperone BiP
may play an active role in quality control within the
secretory pathway. Plant Cell 18, 198–211.
58 Cai H, Yu S, Menon S, Cai Y, Lazarova D, Fu C,
Reinisch K, Hay JC & Ferro-Novick S (2007)
TRAPPI tethers COPII vesicles by binding the coat
subunit Sec23. Nature 445, 941–944.
59 Pucadyil TJ & Schmid SL (2009) Conserved functions
of membrane active GTPases in coated vesicle
formation. Science 325, 1217–1220.
60 Nielsen E, Cheung AY & Ueda T (2008) The
regulatory RAB and ARF GTPases for Vesicular
Trafficking. Plant Physiol 147, 1516–1526.
61 Niemes S, Labs M, Scheuring D, Krueger F,
Langhans M, Jesenofsky B, Robinson DG & Pimpl P
(2010) Sorting of plant vacuolar proteins is initiated in
the ER. Plant J 4, 601–614.
62 Wiederhold K & Fasshauer D (2009) Is assembly of
the SNARE membrane fusion? J Biol Chem 284,
13143–13152.
63 Duman JG & Forte JG (2003) What is the role of
SNARE proteins in membrane fusion? Plant Cell
Physiol 285, 237–249.
FEBS Journal 280 (2013) 979–993 ª 2012 The Authors Journal compilation ª 2012 FEBS
L. Xiang et al.
64 Swanson SJ, Bethke PC & Jones RL (1998) Barley
aleurone cells contain two types of vacuoles:
Characterization of lytic organelles by use of
fluorescent probes. Plant Cell 10, 685–698.
65 Matheson LA, Hanton SL & Brandizzi F (2006)
Traffic between the plant endoplasmic reticulum and
Golgi apparatus: to the Golgi and beyond. Curr Opin
Plant Biol 9, 601–609.
66 Spang A (2009) On vesicle formation and tethering in
the ER-Golgi shuttle. Curr Opin Cell Biol 21,
531–536.
67 Langhans M, Marcote MJ, Pimpl P, Virgili-L
opez G,
Robinson DG & Aniento F (2008) In vivo trafficking
and localization of p24 proteins in plant cells. Traffic
9, 770–785.
68 Jensen D & Schekman R (2011) COPII-mediated
vesicle formation at a glance. J Cell Sci 124, 1–4.
69 Yang YD, Elamawi R, Bubeck J, Pepperkok R,
Ritzenthaler C & Robinson DG (2005) Dynamics of
COPII vesicles and the Golgi apparatus in cultured
Nicotiana tabacum BY-2 cells provides evidence for
transient association of Golgi stacks with endoplasmic
reticulum exit sites. Plant Cell 17, 1513–1531.
70 Russell C & Stagg S (2010) New insights into the
structural mechanisms of the COPII coat. Traffic 11,
303–310.
71 Marti L, Fornaciari S, Renna L, Stefano G &
Brandizzi F (2010) COPII-mediated traffic in plants.
Trends Plant Sci 15, 522–528.
72 Pimpl P, Movafeghi A, Coughlan S, Denecke J,
Hillmer S & Robinson D (2000) In situ localization
and in vitro induction of plant COPI-coated vesicles.
Plant Cell 12, 2219–2236.
73 Donohoe BS, Kang B-H & Staehelin L (2007)
Identification and characterization of COPIa- and
COPIb-type vesicle classes associated with plant and
algal Golgi. Proc Natl Acad Sci USA 104, 163–168.
74 Mancias JD & Goldberg J (2005) Exiting the
endoplasmic reticulum. Traffic 6, 278–285.
75 Neumann U, Brandizzi F & Hawes C (2003) Protein
transport in plant cells: in and out of the Golgi. Ann
Bot 92, 167–180.
76 Hanton SL, Renna L, Bortolotti LE, Chatre L,
Stefano G & Brandizzi F (2005) Diacidic motifs
influence the export of transmembrane proteins from
the endoplasmic reticulum in plant cells. Plant Cell 17,
3081–3093.
77 Schoberer J, Vavra U, Stadlmann J, Hawes C, Mach
L, Steinkellner H & Strasser R (2009) Arginine/lysine
residues in the cytoplasmic tail promote ER export of
plant glycosylation enzymes. Traffic 10, 101–115.
78 Hanton SL, Matheson LA, Chatre L & Brandizzi F
(2009) Dynamic organization of COPII coat proteins
at endoplasmic reticulum export sites in plant cells.
Plant J 57, 963–974.
Vacuolar protein sorting in plant cells
79 Lee HI, Gal S, Newman TC & Raikhel NV (1993) The
Arabidopsis endoplasmic reticulum retention receptor
functions in yeast. Proc Natl Acad Sci USA 90,
11433–11437.
80 Hwang I (2008) Sorting and anterograde trafficking at
the Golgi apparatus. Plant Physiol 148, 673–683.
81 Hawes C, Osterrieder A, Hummel E & Sparkes I
(2008) The plant ER – Golgi interface. Traffic 9,
1571–1580.
82 Connerly PL (2010) How do proteins move through
the Golgi apparatus? Nat Educ 3, 60.
83 Cheng FY, Zamski E, Guo WW, Pharr DM &
Williamson JD (2009) Salicylic acid stimulates
secretion of the normally symplastic enzyme mannitol
dehydrogenase (MTD): a possible defense against
mannitol secreting fungal pathogens. Planta 230,
1093–1103.
84 T€
orm€akangas K, Hadlington JL, Pimpl P, Hillmer S,
Brandizzi F, Teeri TH & Denecke J (2001) A vacuolar
sorting domain may also influence the way in which
proteins leave the endoplasmic reticulum. Plant Cell
13, 2021–2032.
85 Kirchhausen T (2000) Clathrin. Annu Rev Biochem 69,
699–727.
86 Traub L, Bannykh S, Rodel J & Aridor W (1996) AP2-containing clathrin coats assemble on mature
lysosomes. J Cell Biol 135, 1801–1814.
87 Bryant N, Piper R, Weisman L & Stevens T (1998)
Retrograde traffic out of the yeast vacuole to the TGN
occurs via the prevacuolar/endosomal compartment.
J Cell Biol 142, 651–663.
88 Fotin A, Cheng Y, Sliz P, Grigorieff N, Harrison SC,
Kirchhausen T & Walz T (2004) Molecular model for
a complete clathrin lattice from electron
cryomicroscopy. Nature 432, 573–579.
89 Schmid SL (1997) Clathrin-coated vesicle formation
and protein sorting: an integrated process. Annu Rev
Biochem 66, 511–548.
90 McMahon HT & Boucrot E (2011) Molecular
mechanism and physiological functions of clathrinmediated endocytosis. Nat Rev Mol Cell Biol 12,
517–533.
91 Hwang I & Robinson DG (2009) Transport vesicle
formation in plant cells. Curr Opin Plant Biol 12,
660–669.
92 Bandmann V & Homann U (2012) Clathrinindependent endocytosis contributes to uptake of
glucose into BY-2 protoplasts. Plant J 70, 578–584.
93 Gall L, Stan RC, Kress A, Hertel B, Thiel G &
Meckel T (2010) Fluorescent detection of fluid phase
endocytosis allows for in vivo estimation of endocytic
vesicle sizes in plant cells with sub-diffraction
accuracy. Traffic 11, 448–459.
94 Lodish H, Berk A, Zipursky SL, Matsudaira P,
Baltimore D & Darnell J (2000) Molecular
FEBS Journal 280 (2013) 979–993 ª 2012 The Authors Journal compilation ª 2012 FEBS
989
L. Xiang et al.
Vacuolar protein sorting in plant cells
95
96
97
98
99
100
101
102
103
104
105
106
107
990
mechanisms of vesicular traffic. In Molecular Cell
Biology. W.H. Freeman, New York, NY.
Neuhaus J-M & Paris N (2005) Plant vacuoles: from
biogenesis to function. Plant Cell Monogr 1, 63–82.
Craddock CP, Hunter PR, Szakacs E, Hinz G,
Robinson DG & Frigerio L (2008) Lack of a vacuolar
sorting receptor leads to non-specific missorting of
soluble vacuolar proteins in Arabidopsis seeds. Traffic
9, 408–416.
Rojo E, Zouhar J, Carter C, Kovaleva V & Raikhel
NV (2003) A unique mechanism for protein processing
and degradation in Arabidopsis. Proc Natl Acad Sci
USA 100, 7389–7394.
Holwerda BC, Padgett HS & Rogers JC (1992)
Proaleurain vacuolar targeting is mediated by short
contiguous peptide interactions. Plant Cell 4, 307–318.
Koide Y, Matsuoka K, Ohto M & Nakamura K
(1999) The N-terminal propeptide and the C terminus
of the precursor to 20-kilo-dalton potato tuber protein
can function as different types of vacuolar sorting
signals. Plant Cell Physiol 40, 1152–1159.
Nakamura K & Matsuoka K (1993) Protein targeting
to the vacuole in plant cells. Plant Physiol 101, 1–5.
~ez A, Sohn EJ, Robert S,
Sanmartın M, Ord
on
Sanchez-Serrano JJ, Surpin MA, Raikhel NV & Rojo
E (2007) Divergent functions of VTI12 and VTI11 in
trafficking to storage and lytic vacuoles in
Arabidopsis. Proc Natl Acad Sci USA 104, 3645–3650.
Brown JC, Jolliffe NA, Frigerio L & Roberts LM
(2003) Sequence-specific, Golgi-dependent vacuolar
targeting of castor bean 2S albumin. Plant J 36,
711–719.
Frigerio L, Jolliffe NA, Di Cola A, Felipe DH, Paris
N, Neuhaus JM, Lord JM, Ceriotti A & Roberts LM
(2001) The internal propeptide of the ricin precursor
carries a sequence-specific determinant for vacuolar
sorting. Plant Physiol 126, 167–175.
Jolliffe NA, Brown JC, Neumann U, Vicre M, Bachi
A, Hawes C, Ceriotti A, Roberts LM & Frigerio L
(2004) Transport of ricin and 2S albumin precursors
to the storage vacuoles of Ricinus communis
endosperm involves the Golgi and VSR-like receptors.
Plant J 39, 821–833.
Koide Y, Hirano H, Matsuoka K & Nakamura K
(1997) The N-terminal propeptide of the precursor to
sporamin acts as a vacuole-targeting signal even at the
C terminus of the mature part in tobacco cells. Plant
Physiol 114, 863–870.
Maruyama N, Mun LC, Tatsuhara M, Sawada M,
Ishimoto M & Utsumi S (2006) Multiple vacuolar
sorting determinants exist in soybean 11S globulin.
Plant Cell 18, 1253–1273.
Bednarek SY & Raikhel NV (1991) The barley lectin
carboxyl-terminal propeptide is a vacuolar protein
sorting determinant in plants. Plant Cell 3, 1195–1206.
108 Neuhaus JM, Sticher L, Meins F & Boller T (1991) A
short C-terminal sequence is necessary and sufficient
for the targeting of chitinases to the plant vacuole.
Proc Natl Acad Sci USA 88, 100362–110366.
109 Schroeder MR, Borkhsenious ON, Matsuoka K,
Nakamura K & Raikhel NV (1993) Colocalization of
barley lectin and sporamin in vacuoles of transgenic
tobacco plants. Plant Physiol 101, 451–458.
110 Nishizawa K, Maruyama N, Satoh R, Fuchikami Y,
Higasa T & Utsumi S (2003) A C-terminal sequence of
soybean b-conglycinin a-subunit acts as a vacuolar
sorting determinant in seed cells. Plant J 34, 647–659.
111 Petruccelli S, Molina MI, Lareu FJ & Circosta A
(2007) Two short sequences from amaranth 11S
globulin are sufficient to target green fluorescent
protein and beta-glucuronidase to vacuoles in
Arabidopsis cells. Plant Physiol Biochem 45, 400–409.
112 Jolliffe NA, Craddock CP & Frigerio L (2005)
Pathways for protein transport to seed storage
vacuoles. Biochemistry 33, 1016–1018.
113 Vitale A & Hinz G (2005) Sorting of proteins to
storage vacuoles: how many mechanisms? Trends Plant
Sci 10, 316–323.
114 Nishizawa K, Maruyama N & Utsumi S (2006)
The C-terminal region of a subunit of soybean
b-conglycinin contains two types of vacuolar sorting
determinants. Plant Mol Biol 62, 111–125.
115 Perez-Sala D, Boya P, Ramos I, Herrera M &
Stamatakis K (2009) The C-terminal sequence of
RhoB directs protein degradation through an endolysosomal pathway. PLoS One 4, e8117.
116 Behnke J, Schneppenheim J, Koch-Nolte F, Haag F,
Saftig P & Schroder B (2011) Signal-peptide-peptidaselike 2a (SPPL2a) is targeted to lysosomes/late
endosomes by a tyrosine motif in its C-terminal tail.
FEBS Lett 585, 2951–2957.
117 Gough NR, Zweifel ME, Martinez-Augustin O,
Aguilar RC, Bonifacino JS & Fambrough DM (1999)
Utilization of the indirect lysosome targeting pathway
by lysosome associated membrane proteins (LAMPs)
is influenced largely by the C-terminal residue of their
GYXXΦ targeting signals. J Cell Sci 112, 4257–4269.
118 Vitale A & Chrispeels M (1992) Sorting of proteins to
vacuoles in plant cells. BioEssays 14, 151–160.
119 Hinz G, Menze A, Hohl I & Vaux D (1997) Isolation
of prolegumin from developing pea seeds: Its binding
to endomembranes and assembly into prolegumin
hexamers in the protein storage vacuole. J Exp Bot 48,
139–149.
120 Kirsch T, Paris N, Butler JM, Beevers L & Rogers JC
(1994) Purification and initial characterization of a
potential plant vacuolar targeting receptor. Proc Natl
Acad Sci USA 91, 3403–3407.
121 Seaman MNJ, Marcusson EG, Cereghino JL & Emr
SD (1997) Endosome to Golgi retrieval of the
FEBS Journal 280 (2013) 979–993 ª 2012 The Authors Journal compilation ª 2012 FEBS
L. Xiang et al.
122
123
124
125
126
127
128
129
130
131
132
vacuolar protein sorting receptor, Vps10p, requires the
function of the VPS29, VPS30, and VPS35 gene
products. J Cell Biol 137, 79–92.
Wang H, Rogers JC & Jiang L (2011) Plant RMR
proteins: unique vacuolar sorting receptors that couple
ligand sorting with membrane internalization. FEBS J
278, 59–68.
Ahmed SU, Rojo E, Kovaleva V, Venkataraman S,
Dombrowski JE, Matsuoka K & Raikhel NV (2000)
The plant vacuolar sorting receptor AtELP is involved
in transport of NH(2)-terminal propeptide-containing
vacuolar proteins in Arabidopsis thaliana. J Cell Biol
149, 1335–1344.
Happel N, Honing S, Neuhaus JM, Paris N, Robinson
DG & Holstein SE (2004) Arabidopsis mu A-adaptin
interacts with the tyrosine motif of the vacuolar
sorting receptor VSR-PS1. Plant J 37, 678–693.
Kalthoff C, Alves J, Urbanke C, Knorr R &
Ungewickell EJ (2002) Unusual structural organization
of the endocytic proteins AP180 and EPSIN 1. J Biol
Chem 277, 8209–8216.
Song J, Lee MH, Lee G-J, Yoo CM & Hwang I
(2006) Arabidopsis EPSIN1 plays an important role in
vacuolar trafficking of soluble cargo proteins in plant
cells via interactions with clathrin, AP-1, VTI11, and
VSR1. Plant Cell 18, 2258–2274.
Oliviusson P, Heinzerling O, Hillmer S, Hinz G, Tse
YC, Jiang L & Robinson DG (2006) Plant retromer,
localized to the prevacuolar compartment and
microvesicles in Arabidopsis may interact with
vacuolar sorting receptors. Plant Cell 18,
1239–1252.
Miao Y, Yan PK, Kim H, Hwang I & Jiang L (2006)
Localization of green fluorescent protein fusions with
the seven Arabidopsis vacuolar sorting receptors to
prevacuolar compartments in tobacco BY-2 cells.
Plant Physiol 142, 945–962.
da Silva LL, Taylor JP, Hadlington JL, Hanton SL,
Snowden CJ, Fox SJ, Foresti O, Brandizzi F &
Denecke J (2005) Receptor salvage from the
prevacuolar compartment is essential for efficient
vacuolar protein targeting. Plant Cell 17, 132–148.
Hara-Nishimura I, Shimada T, Hatano K, Yakeuchi
Y & Nishimura M (1998) Transport of storage
proteins to protein storage vacuoles is mediated by
large precursor-accumulating vesicles. Plant Cell 10,
825–836.
Shimada T, Watanabe E, Tamura K, Hayashi Y,
Nishimura M & Hara-Nishimura I (2002) A vacuolar
sorting receptor PV72 on the membrane of vesicles
that accumulate precursors of seed storage proteins
(PAC vesicles). Plant Cell Physiol 43, 1086–1095.
Molina MI, Otegui M & Petruccelli S (2006)
Sunflower storage proteins are transported in dense
vesicles that contain proteins homologous to the
Vacuolar protein sorting in plant cells
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
FEBS Journal 280 (2013) 979–993 ª 2012 The Authors Journal compilation ª 2012 FEBS
pumpkin vacuolar sorting receptor PV 72. J Biotechnol
9, 325–330.
Shimada T, Fuji K, Tamura K, Kondo M, Nishimura
M & Hara-Nishimura I (2003) Vacuolar sorting
receptor for seed storage proteins in Arabidopsis
thaliana. Proc Natl Acad Sci USA 100, 16095–16100.
Jiang L & Rogers JC (2003) Sorting of lytic enzymes
in the plant Golgi apparatus. Annu Plant Rev 9,
114–140.
Park J, Oufattole M & Rogers J (2007) Golgimediated vacuolar sorting in plant cells: RMR
proteins are sorting receptors for the protein
aggregation/membrane internalization pathway. Plant
Sci 172, 728–745.
Mahon P & Bateman A (2000) The PA domain: a
protease-associated domain. Protein Sci 9, 1930–1934.
Hinz G, Colanesi S, Hillmer S, Rogers JC &
Robinson DG (2007) Localization of vacuolar
transport receptors and cargo proteins in the Golgi
apparatus of developing Arabidopsis embryos. Traffic
8, 1452–1464.
Park M, Lee D, Lee G-J & Hwang I (2005) AtRMR1
functions as a cargo receptor for protein trafficking to
the protein storage vacuole. J Cell Biol 170, 757–767.
Gillespie J, Rogers SW, Deery M, Dupree P & Rogers
JC (2005) A unique family of proteins associated with
internalized membranes in protein storage vacuoles of
the Brassicaceae. Plant J 41, 429–441.
Shen Y, Wang J, Ding Y, Lo SW, Gouzerh G, Neuhaus
J-M & Jiang LW (2011) The rice RMR1 associates with
a distinct prevacuolar compartment for the protein
storage vacuole pathway. Mol Plant 4, 854–868.
Hirst J, Barlow LD, Francisco GC, Sahlender DA,
Seaman MNJ, Dacks JB & Robinson MS (2011) The
fifth adaptor protein compex. PLoS Biol 9, e1001170.
Boehm M & Bonifacino JS (2001) Adaptin: the final
recount. Mol Biol Cell 12, 2907–2920.
Dacks JB, Poon PP & Field MC (2008) Phylogeny of
endocytic components yields insight into the process
of nonendosymbiotic organelle evolution. Proc Natl
Acad Sci USA 105, 588–593.
Robinson MS & Bonifacino JS (2001) Adaptor-related
proteins. Curr Opin Cell Biol 13, 444–453.
Bonifacino JS & Traub LM (2003) Signals for sorting
of transmembrane protein to endosomes and
lysosomes. Annu Rev Biochem 72, 395–447.
Sanderfoot AA, Ahmed SU, Marty-Mazars D,
Rapoport I, Kirchhausen T, Marty F & Raikhel NV
(1998) A putative vacuolar cargo receptor partially
colocalizes with AtPEP12p on a prevacuolar
compartment in Arabidopsis roots. Proc Natl Acad Sci
USA 95, 9920–9925.
Nakatsu F & Ohno H (2003) Adaptor protein
complexes as the key regulators of Protein sorting in
the post-Golgi network identification of AP complexes
991
L. Xiang et al.
Vacuolar protein sorting in plant cells
148
149
150
151
152
153
154
155
156
157
158
992
recognition of sorting signals by AP complexes. Cell
Struct Funct 429, 419–429.
Owen DJ, Vallis Y, Pearse BM, McMahon HT &
Evans PR (2000) The structure and function of the
beta 2-adaptin appendage domain. EMBO J 19,
4216–4227.
Slepnev VI & De Camili P (2000) Accessory factors in
clathrin-dependent synaptic vesicle endocytosis. Nat
Rev Neurosci 1, 161–172.
Stepp JD, Huang K & Lemmon SK (1997) The yeast
adaptor protein complex, AP-3, is essential for the
efficient delivery of alkaline phosphatase by the
alternate pathway to the vacuole. J Cell Biol 139, 1761
–1774.
Zwiewka M, Feraru E, M€
oller B, Hwang I, Feraru
MI, Kleine-Vehn J, Weijers D & Friml J (2011) The
AP-3 adaptor complex is required for vacuolar
function in Arabidopsis. Cell Res 21, 1711–1722.
Feraru E, Paciorek T, Feraru MI, Zwiewka M, De
Groodt R, De Rycke R, Kleine-Vehn J & Friml J
(2010) The AP-3 beta adaptin mediates the biogenesis
and function of lytic vacuoles in Arabidopsis. Plant
Cell 22, 2812–2824.
Niihama M, Takemoto N, Hashiguchi Y, Tasaka M
& Morita MT (2009) ZIP genes encode proteins
involved in membrane trafficking of the TGN-PVC/
vacuoles. Plant Cell Physiol 50, 2057–2068.
Burgos PV, Mardones GA, Rojas AL, daSilva LLP,
Prabhu Y, Hurley JH & Bonifacino JS (2010)
Sorting of the Alzheimer’s disease amyloid precursor
protein mediated by the AP-4 complex. Dev Cell 18,
425–436.
Abou Jamra R, Philippe O, Rass-Rothschild A,
Eck SH, Graf E, Buchert R, Borck G, Ekici A,
Brockschmidt FF, Nothen MM, Munnich A, Strom
TM, Reis A & Colleaux L (2011) Adaptor protein
complex 4 deficiency causes severe autosomal-recessive
intellectual disability, progressive spastic paraplegia,
shy character, and short stature. J Hum Genet 88,
788–795.
Moreno-De-Luca A et al. (2011) Adaptor protein
complex-4 (AP-4) deficiency causes a novel autosomal
recessive cerebral palsy syndrome with microcephaly
and intellectual disability. J Med Genet 48,
141–144.
Janvier K, Kato Y, Boehm M, Rose JR, Martina JA,
Kim B-Y, Venkatesan S & Bonifacino JS (2003)
Recognition of dileucine-based sorting signals from
HIV-1 Nef and LIMP-II by the AP-1 gamma-sigma1
and AP-3 delta-sigma3 hemicomplexes. J Cell Biol
163, 1281–1290.
Badolato R & Parolini S (2007) Novel insights from
adaptor protein 3complex deficiency. J Allergy Clin
Immunol 120, 735–741.
159 Robinson DG, Oliviusson P & Hinz G (2005) Protein
sorting to the storage vacuoles of plants: a critical
appraisal. Traffic 6, 615–625.
160 Chrispeels MJ (1983) The Golgi apparatus mediates
the transport of phytohemagglutinin to the protein
bodies in bean cotyledons. Planta 158, 140–151.
161 Hohl I, Robinson DG, Chrispeels MJ & Hinz G
(1996) Transport of storage proteins to the vacuole is
mediated by vesicles without a clathrin coat. J Cell Sci
109, 2539–2550.
162 Kim WT, Franceschi VR, Krishnan HB & Okita TW
(1988) Formation of wheat protein bodies:
involvement of the Golgi apparatus in gliadin
transport. Planta 176, 173–183.
163 Hinz G, Hillmer S, Baumer M & Hohl I (1999)
Vacuolar storage proteins and the putative vacuolar
sorting receptor BP-80 exit the golgi apparatus of
developing pea cotyledons in different transport
vesicles. Plant Cell 11, 1509–1524.
164 Jiang L, Phillips TE, Hamm CA, Drozdowicz YM,
Rea PA, Maeshima M, Rogers SW & Rogers JC
(2001) The protein storage vacuole: a unique
compound organelle. J Cell Biol 155, 991–1002.
165 Robinson DG, Hinz G & Holstein SEH (1998) The
molecular characterization of transport vesicle. Plant
Mol Biol 38, 49–76.
166 Tse YC, Mo B, Hillmer S, Zhao M, Lo SW,
Robinson DG & Jiang L (2004) Identification of
multivesicular bodies as prevacuolar compartments in
Nicotiana tabacum BY-2 cells. Plant Cell 16, 672–693.
167 Li L, Shimada T, Takahashi H, Ueda H, Fukao Y,
Kondo M, Nishimura M & Hara-Nishimura I (2006)
MAIGO2 is involved in exit of seed storage proteins
from the endoplasmic reticulum in Arabidopsis
thaliana. Plant Cell 18, 3535–3547.
168 Fuji K, Shimada T, Takahashi H, Tamura K,
Koumoto Y, Utsumi S, Nishizawa K, Maruyama N
& Hara-Nishimura I (2007) Arabidopsis vacuolar
sorting mutants (green fluorescent seed) can be
identified efficiently by secretion of vacuole-targeted
green fluorescent protein in their seeds. Plant Cell 19,
597–609.
169 Wenzel D, Schauermann G, Von L€
upke A & Hinz G
(2005) The cargo in vacuolar storage protein transport
vesicles is stratified. Traffic 6, 45–55.
170 Hara-Nishimura I, Matsushima R, Shimada T &
Nishimura M (2004) Diversity and formation of
endoplasmic reticulum-derived compartments in
plants. Are these compartments specific to plant cells?
Plant Physiol 136, 3435–3439.
171 Toyooka K, Okamoto T & Minamikawa T (2000)
Mass transport of proform of a KDEL-tailed cysteine
proteinase (SH-EP) to protein storage vacuoles by
endoplasmic reticulum-derived vesicle is involved in
FEBS Journal 280 (2013) 979–993 ª 2012 The Authors Journal compilation ª 2012 FEBS
L. Xiang et al.
172
173
174
175
176
177
178
179
180
181
182
183
protein mobilization in germinating seeds.
J Cell Biology 148, 453–464.
Mitsuhashia N, Hayashib Y, Koumotoa Y, Shimadaa
T, Fukasawa-Akadac T, Nishimurab M & HaraNishimura I (2001) A novel membrane protein that is
transported to protein storage vacuoles via precursoraccumulating vesicles. Plant Cell 13, 2361–2372.
Mori T, Maruyama N, Nishizawa K, Higasa T,
Yagasaki K, Ishimoto M & Utsumi S (2004) The
composition of newly synthesized proteins in the
endoplasmic reticulum determines the transport
pathways of soybean seed storage proteins. Plant J 40,
238–249.
Takahashi H, Saito Y, Kitagawa T, Morita S,
Masumura T & Tanaka K (2005) A novel vesicle
derived directly from endoplasmic reticulum is
involved in the transport of vacuolar storage proteins
in rice endosperm. Plant Cell Physiol 46, 245–249.
Robinson DG, Hoh B, Hinz G & Jeong BK (1995)
One vacuole or two vacuoles: do protein storage
vacuoles arise de novo during pea cotyledon
development? J Plant Physiol 145, 654–655.
Van Der Wilden W, Herman EM & Chrispeels MJ
(1980) Protein bodies of mung bean cotyledons as
autophagic organelles. Proc Natl Acad Sci USA 77,
428–432.
Shimada T, Nishimura M & Hara-Nishimura I (1994)
Small GTP-binding proteins are associated with the
vesicles targeting to vacuoles in developing pumpkin
cotyledons. Plant Cell Physiol 35, 995–1001.
Rouille Y, Rohn W & Hoflack B (2000) Targeting of
lysosomal proteins. Semin Cell Dev Biol 11, 165–171.
Ghosh P, Dahms NM & Kornfeld S (2003) Mannose
6-phosphate receptors: new twists in the tale. Nat Rev
Mol Cell Biol 4, 202–212.
Doray B, Ghosh P, Griffith J, Geuze HJ & Kornfeld S
(2002) Cooperation of GGAs and AP-1 in packaging
MPRs at the trans-Golgi network. Science 297,
1700–1703.
Deloche O, Yeung BG, Payne GS & Schekman R
(2001) Vps10p transport from the trans-Golgi network
to the endosome is mediated by clathrin-coated
vesicles. Mol Biol Cell 12, 475–485.
Costaguta G, Stefan CJ, Bensen ES, Emr SD & Payne
GS (2001) Yeast GGA coat proteins function with
clathrin in Golgi to endosome transport. Mol Biol Cell
12, 1885–1896.
Matsuoka K & Neuhaus JM (1999) Cis-elements of
protein transport to the plant vacuoles. J Exp Bot 50,
165–174.
Vacuolar protein sorting in plant cells
184 Paris N & Neuhaus J-M (2002) BP-80 as a vacuolar
sorting receptor. Plant Mol Biol 50, 903–914.
185 Raiborg C, Rusten TE & Stenmark H (2003) Protein
sorting into multivesicular endosomes. Curr Opin Cell
Biol 15, 446–455.
186 Maxfield FR & McGraw TE (2004) Endocytic
recycling. Nat Rev Mol Cell Biol 5, 121–132.
187 Seaman MNJ (2005) Recycle your receptors with
retromer. Trends Cell Biol 15, 68–75.
188 Reczek D, Schwake M, Schroder J, Hughes H, Blanz
J, Jin X, Brondyk W, Van Patten S, Edmunds T &
Saftig P (2007) LIMP-2 is a receptor for lysosomal
mannose-6-phosphate-independent targeting of betaglucocerebrosidase. Cell 131, 770–783.
189 Iwaki T, Hosomi A, Tokudomi S, Kusunoki Y, Fujita
Y, Giga-Hama Y, Tanaka N & Takegawa K (2006)
Vacuolar protein sorting receptor in
Schizosaccharomyces pombe. Microbiology 152,
1523–1532.
190 Wolfenstetter S, Wirsching P, Dotzauer D, Schneider
S & Sauer N (2012) Routes to the tonoplast: the
sorting of tonoplast transporters in Arabidopsis
mesophyll protoplasts. Plant Cell 24, 215–232.
191 Braulke T & Bonifacino JS (2009) Sorting of
lysosomal proteins. Biochim Biophys Acta 1793,
605–614.
192 Matsushima R, Hayashi Y, Yamada K, Shimada T,
Nishimura M & Hara-Nishimura I (2003) The ER
body, a novel endoplasmic reticulum-derived structure
in Arabidopsis. Plant Cell Physiol 44, 661–666.
193 Herman EM (2008) Endoplasmic reticulum bodies:
solving the insoluble. Curr Opin Plant Biol 11,
672–679.
194 Teckman JH & Perlmutter DH (2000) Retention of
mutant a1-antitrypsin Z in endoplasmic reticulum is
associated with an autophagic response. Am J Physiol
Gastrointest Liver Physiol 279, 961–974.
195 Herman EM & Schmidt M (2004) Endoplasmic
reticulum to vacuole trafficking of endoplasmic
reticulum bodies provides an alternate pathway for
protein transfer to the vacuole. Plant Physiol 136,
3440–3446.
196 Hayashi Y, Yamada K, Shimada T, Matsushima R,
Nishizawa NK, Nishimura M & Hara-Nishimura I
(2001) A proteinase-storing body that prepares for cell
death or stresses in the epidermal cells of Arabidopsis.
Plant Cell Physiol 42, 894–899.
FEBS Journal 280 (2013) 979–993 ª 2012 The Authors Journal compilation ª 2012 FEBS
993