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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
Absolute plastid area, outer mesocarp
hp2
30000
20000
10000
0
0
100000
Cell area
200000
Absolute plastid area, inner mesocarp
50000
Plastid area
Relative plastid compartment
WT
hp2
40000
30000
30
25.52
25
20
15
10
8.35
5
0
WT
20000
Plastid compartment (%)
Plastid area
40000
WT Com
hp2j Com
Genotype
10000
0
0
100000
200000
Cell area
300000
Fruit-specific silencing of LsDET1 also leads to increased cellular
plastid compartment
wild type
2A11p:DET1i
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(Unpublished data by E. Enfissi)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
3000
6
4
2000
0
20000
40000
0
T56
60000
TFM7
0
14
8000
12
7000
800
700
600
500
400
300
200
40000
80000
4000
6
3000
4
2000
2
1000
0
T56
TFM7
0
14000
700
14
12000
500
400
300
200
12
40000
80000 120000 160000
Cell area (μm2)
4000
4
0
0
6000
6
0
120000
8000
8
2
80000
10000
10
100
40000
Total plastid area per cell
(μm2)
Average plastid size (μm2)
16
Inner mesocarp
800
600
60000
5000
8
120000
40000
6000
10
0
0
20000
Total plastid area per cell
(μm2)
900
Average plastid size (μm2)
9000
Number of plastids per cell
16
Outer mesocarp
1000
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
2000
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