Altering light perception during tomato fruit ripening significantly affects antioxidant accumulation

LW+UV

LW HW

D FR R B

Chloroplasts “compartment size”: organelle population signalling, and the uncovering of chloroplast “master

switches”.

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

hp2j

WT

Absolute plastid area, inner mesocarp

0

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40000

50000

0 100000 200000 300000

Cell area

Pla

stid

are

a

hp2

WT

Absolute plastid area, outer mesocarp

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40000

0 100000 200000Cell area

Pla

stid

are

a

WT

hp2

Loss of LsDET1 leads to at least a doubling in plastid complement

Relative plastid compartment

8.35

25.52

0

5

10

15

20

25

30

WT Com hp2j ComGenotype

Pla

stid

co

mp

art

me

nt (

%)

Fruit-specific silencing of LsDET1 also leads to increased cellular plastid compartment

wild type2A11p:DET1

i

TFM7p:DET1iP119p:DET1

i

0

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T56 2A11 TFM7 P119

Pla

stom

e/n

ucl

ear

genom

e r

ati

o

(Unpublished data by E. Enfissi)

(Plants of Davuluri et al. 2005,

Nature Biotech. 7: 890-895)

The increase can also be measured as plastome/genome ratio

Importantly, increased plastid compartment can be achieved by combinations of increases in plastid size and number

0

100

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0 20000 40000 60000

Num

ber

of

plas

tids

per

cell

Tot

al p

last

id a

rea

per

cell

(μm

2)

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0 20000 40000 60000

TFM7T56 (WT)TFM7T56 (WT)

Ave

rage

pla

stid

siz

e (μ

m2)

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T56 TFM7

Ave

rage

pla

stid

siz

e (μ

m2)

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20

T56 TFM7

Exoca

rp

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0 40000 80000 120000

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0 40000 80000 120000

Num

ber

of

pla

stid

s p

er

cell

Avera

ge p

last

id s

ize (

μm

2)

Tota

l p

last

id a

rea p

er

cell

(μm

2)

0

2

4

6

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16

T56 TFM7

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0 40000 80000 120000 160000

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0 40000 80000 120000 160000

Cell area (μm2) Cell area (μm2)

Num

ber

of

pla

stid

s p

er

cell

Avera

ge p

last

id s

ize

(μm

2)

Tota

l p

last

id a

rea p

er

cell

(μm

2)

Genotype

0

2

4

6

8

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14

16

T56 TFM7

Oute

r meso

carp

Inner m

eso

carp

Plastid “growth” matters

Tight control of the total cellular plastid complement has long been known in cereal leaves

Since plastid growth results from the expression of nuclear genes, this implies “plastid compartment size” retrograde signalling

(Ellis and Leech 1985,Planta 165: 120-125)

(Pyke and Leech 1987,Planta 170: 416-420)

3dD +1dL +2dL

+3dL+4dL +5dL

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)

Plastid division

0.0

0.5

1.0

1.5

2.0

Mer

0

Mer

1

Mer

2

Mer

6

Mer

24

Mer

48

Mer

72

Cot

0

Cot

1

Cot

6

Rel

ativ

e ex

pre

ssio

n

ARC5

FtsZ

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.

Combined examination of biochemically-unrelated chloroplast biogenesis genes reveals the existence of “modules” of

corregulated genes.

TIC 110