Evolutionary Significance
Of Polyploidy In The New
Zealand Flora
Brian Murray
School of Biological Sciences
The University of Auckland
NEW ZEALAND
http://nzprn.otago.ac.nz/wiki/bin/view/NZPRN/WebHome
NZ chromosome numbers are high
• High incidence of
polyploidy:
-90.9% have n > 10
-73.0% have n > 14
• Even numbers
more frequent than
odd
[polyploids
Many NZ angiosperm species are:
Palaeopolyploids –
• Polyploids of more ancient origin
• History is obscured by the absence of obvious diploid relatives
• Identification via genome sequencing
–Arabidopsis, Oryza, Vitis, etc.
Others are:
Neopolyploids –
• Polyploids of relatively recent origin
• Similar/closely related to extant diploids (or lower polyploids)
Polyploidy in the 10 largest NZ
angiosperm genera
Genus
No. polyploid/Total counted %polyploid
Veronica
Carex
Celmisia
Coprosma
Epilobium
Ranunculus
Myosotis
Poa
Olearia
Aciphylla
35/104
holocentric so excluded
70/70
16/58
0/45
36/38
11/11
34/34
34/34
0/21
34
100
28
0
95
100
100
100
0
Have the neopolyploids arisen autochthonously?
• Half of genera analyzed contained neopolyploids
– 40 genera: all species have the same chromosome number
– 42 genera: two or more ploidy levels
• Intraspecific polyploid variation in NZ endemic species
–
–
–
–
Veronica (V. diosmifolia, V. odora and V. pinguifolia)
Lobelia angulata
Crassula ruamahanga
Plantago lanigera, P. unibracteata
Are the NZ polyploids autoploids or alloploids?
Autoploids –
• Multiple copies of same
genome
• Random chromosome synapsis
• Multivalent-forming
Alloploids –
• Multiple copies of genomes
that are sufficiently different
to prevent pairing between them
• Bivalent-forming
Most NZ polyploid species are bivalentforming
•
•
•
Meiotic metaphase I is illustrated
for 201 polyploid species in 77
genera
191 species are bivalent-forming
10 species are multivalent- forming
–
Veronica (6), Pomaderris (2), Myoporum (1),
and Myosotis (1)
Is the frequency of NZ autoploidy being
underestimated?
• Does meiotic chromosome pairing give the ‘true’ story?
• Some NZ species radiations such as Veronica have
diversified from a single colonizing genotype
– Low interspecific sequence variation
– Expect homoploid (diploid) hybrids rather than polyploid hybrids
• Examples where morphology and phylogeny suggest autoploidy
– But bivalent-forming, e.g. 20x Lobelia angulata
– Or multivalent-forming at very low frequency e.g. 4x Veronica odora.
• Low multivalent frequency in Lobelia, Myoporum and Myosotis
is not a consequence of a low chiasma frequency
Has there been widespread genomic differentiation in
examples of autochthonous polyploids?
• NZ Plantago
• Six ploidy levels, 2x, (4x), 8x, 10x, 12x
and 16x
– Autoploid series?
– But both 8x and 16x species are
bivalent-forming = alloploidy?
Plantago molecular cytogenetics
• Genome size measurements
• Fluorescence in situ hybridization (mitotic and meiotic)
• Homologous sequences hybridize to the probe, allowing
identification of specific sequences and similar genomes
• Two approaches: GISH and FISH
• GISH: Use whole genomic DNA of diploids to probe/paint
the chromosomes of related polyploids
• FISH: Use specific sequences (rDNA) to locate 45S and
5S rDNA sites as a proxy for genome reorganization or
differentiation
Genome size in Plantago
Species
Ploidy
P. lanigera
P. spathulata
P. picta
P. raoulii
P. triandra
P. unibracteata
P. unibracteata
P. n. sp.
2x
8x
8x
8x
8x
10x
12x
16x
C-value Cx-value
3.87
9.03
9.35
9.91
10.52
14.13
17.51
17.95
1.94
1.13
1.16
1.24
1.32
1.41
1.46
1.12
Significant genome downsizing in the
transition from 2x to 8x but not 10x to
12x unibracteata.
GISH analyses of P. spathulata
DAPI
lanigera
probe
triandra
probe
(left)
obconica
probe
(right)
Summary of GISH analysis
• The diploids P. lanigera and P. obconica have similar genomes but
different to P. triantha
• All 8x species are alloploids containing 2 copies of P. lanigera/ P.
obconica, 2 copies of P. triantha plus 4 copies of unidentified
genome(s)
• 12x unibracteata is an alloploid containing 2 copies of the P. lanigera
genome
• 16x P. n. sp. Seems to be an alloploid with 4 copies of the P. lanigera
and 4 copies of the P. triantha genome
2x
LL/OO and TT
8x
LLTT????
12x
LL??????????
16x
LLLLTTTT????????
FISH analysis of P.
spathulata
DAPI stained
chromosomes of P.
spathulata 8x
The same cell probed with
45S rDNA (green) and 5S
rDNA (red) probes
P. lanigera 2x
P. spathulata 8x
P. picta 8x
P. n. sp. 16x
P. raoulii 8x
P. triandra 8x
FISH localization of 45S (green) and 5S (red) rDNA loci in Plantago
Meiotic metaphase 1 in 8x
P. spathulata
The ‘lanigera’ genome
painted green in ‘B’ with
GISH.
Neither of the rDNA
probes (red and green in
‘C’) hybridizes to the
‘lanigera’ chromosomes
(arrowed).
Conclusions
• Polyploidy is widespread in the NZ flora with evidence for
autochthonous origins in many cases.
• Polyploidy is associated with many of the species radiations in
NZ angiosperms, but some have radiated at the diploid level.
• There is a predominance of alloploids (bivalent-pairing) despite
low levels of sequence differentiation and possible origins
from a single colonizer.
• Molecular cytogenetic analysis of the endemic Plantago species
strongly suggests that they are alloploids and that there has
been significant genomic reorganization associated with
speciation.
• Genome reorganization has been important for the
diploidization process.
Acknowledgements
Charles Wong for the beautiful GISH and FISH images.
Ross Ferguson and Jingli Li (The NZ Institute for Plant and
Food Research) for help with the flow cytometry.
Heidi Meudt (Museum of New Zealand Te Papa Tongarewa)
Mei Lin Tay and Phil Garnock-Jones (Victoria University of
Wellington) for plant material and for sharing their
knowledge of the genus Plantago.