Chloroplasts “compartment size”: organelle population signalling,
and the uncovering of chloroplast “master switches”.
Altering light perception during tomato fruit ripening
significantly affects antioxidant accumulation
LW+UV
D
LW
FR
HW
R
B
A tomato mutant with enhanced antioxidants (hp2)
- shows enhanced plastid development, and
- is defective in a repressors of photomorphogenesis (LsDET1)
hp2j
WT
A cell’s plastid complement is dramatically affected by loss of LsDET1
WT
hp2j
Loss of LsDET1 leads to at least a doubling in plastid complement
A b so lute p la stid a re a , o ute r m e so ca rp
h p2
30000
20000
10000
0
0
100000
200000
C e ll a re a
A b so lute p la stid a re a , inne r m e so ca rp
50000
h p2
P la stid a re a
R e la tive p la s tid c o m p a rtm e nt
WT
40000
30000
30
2 5 .5 2
25
20
15
10
8 .3 5
5
0
WT
20000
P la s tid c o m p a rtm e n t (% )
P la stid a re a
40000
W T C om
hp 2 j C o m
G e no typ e
10000
0
0
100000
200000
C e ll a re a
300000
Fruit-specific silencing of LsDET1 also leads to increased cellular
plastid compartment
2A11p:DET1i
wild type
Plastome/nuclear genome ratio
1200
1000
800
600
400
TFM7p:DET1i
P119p:DET1i
200
0
T56
2A11
TFM7
P119
(Unpublished data by E. Enfissi)
The increase can also be measured as plastome/genome(Plants
ratio
of
Davuluri et al. 2005,
Nature Biotech. 7: 890-895)
400
300
200
100
9000
18
8000
16
7000
14
5000
10
4000
8
6
3000
4
2000
20000
40000
Average plastid size (μm2)
800
700
600
500
400
300
200
0
16
9000
14
8000
12
7000
0
40000
80000
4000
6
3000
4
2000
2
1000
0
T56
TFM7
0
14000
700
14
12000
Average plastid size (μm2)
16
500
400
300
200
100
12
0
40000
80000
120000 160000
Cell area (μm2)
80000
120000
10000
10
8000
8
6000
6
4000
4
2
2000
0
0
40000
Inner mesocarp
800
600
60000
5000
8
120000
40000
6000
10
0
0
20000
Total plastid area per cell
(μm2)
Number of plastids per cell
900
TFM7
Outer mesocarp
1000
0
T56
60000
Total plastid area per cell
(μm2)
0
Number of plastids per cell
1000
0
0
TFM7
T56 (WT)
6000
12
2
100
Plastid “growth”
matters
20
Total plastid area per cell
(μm2)
Average plastid size (μm2)
Number of plastids per cell
500
Exocarp
Importantly,
increased plastid
compartment can
be achieved by
combinations of
increases in
plastid size and
number
0
T56
TFM7
Genotype
0
40000
80000 120000 160000
Cell area (μm2)
Tight control of the total cellular plastid complement has long
been known in cereal leaves
(Pyke and Leech 1987,
Planta 170: 416-420)
(Ellis and Leech 1985,
Planta 165: 120-125)
Since plastid growth results from the expression of nuclear
genes, this implies “plastid compartment size” retrograde
signalling
Chloroplast biogenesis can be followed as part of a whole
transcriptome analysis of leaf initiation in the light
(distinguishing the shoot apex and the cotyledons)
3dD
+3dL
+1dL
+4dL
+2dL
+5dL
Indeed light upregulates specifically in the shoot apex components
of the plastid division process, but this is unlikely to be the driving
force in chloroplast accumulation. Many other processes occur.
Plastid division
ARC5
FtsZ
1.5
1.0
0.5
Cot 6
Cot 1
Cot 0
Mer 72
Mer 48
Mer 24
Mer 6
Mer 2
Mer 1
0.0
Mer 0
Relative expression
2.0
Combined examination of biochemically-unrelated chloroplast biogenesis
genes reveals the existence of “modules” of corregulated genes.
TIC
110