Abstract
BACKGROUND: We have studied the impact of carbohydrate-starvation on the acclimation response to high light using Arabidopsis thaliana double mutants strongly impaired in the day- and night path of photoassimilate export from the chloroplast. A complete knock-out mutant of the triose phosphate/phosphate translocator (TPT; tpt-2 mutant) was crossed to mutants defective in (i) starch biosynthesis (adg1-1, pgm1 and pgi1-1; knock-outs of ADP-glucose pyrophosphorylase, plastidial phosphoglucomutase and phosphoglucose isomerase) or (ii) starch mobilization (sex1-3, knock-out of glucan water dikinase) as well as in (iii) maltose export from the chloroplast (mex1-2). RESULTS: All double mutants were viable and indistinguishable from the wild type when grown under low light conditions, but--except for sex1-3/tpt-2--developed a high chlorophyll fluorescence (HCF) phenotype and growth retardation when grown in high light. Immunoblots of thylakoid proteins, Blue-Native gel electrophoresis and chlorophyll fluorescence emission analyses at 77 Kelvin with the adg1-1/tpt-2 double mutant revealed that HCF was linked to a specific decrease in plastome-encoded core proteins of both photosystems (with the exception of the PSII component cytochrome b559), whereas nuclear-encoded antennae (LHCs) accumulated normally, but were predominantly not attached to their photosystems. Uncoupled antennae are the major cause for HCF of dark-adapted plants. Feeding of sucrose or glucose to high light-grown adg1-1/tpt-2 plants rescued the HCF- and growth phenotypes. Elevated sugar levels induce the expression of the glucose-6-phosphate/phosphate translocator2 (GPT2), which in principle could compensate for the deficiency in the TPT. A triple mutant with an additional defect in GPT2 (adg1-1/tpt-2/gpt2-1) exhibited an identical rescue of the HCF- and growth phenotype in response to sugar feeding as the adg1-1/tpt-2 double mutant, indicating that this rescue is independent from the sugar-triggered induction of GPT2. CONCLUSIONS: We propose that cytosolic carbohydrate availability modulates acclimation to high light in A. thaliana. It is conceivable that the strong relationship between the chloroplast and nucleus with respect to a co-ordinated expression of photosynthesis genes is modified in carbohydrate-starved plants. Hence carbohydrates may be considered as a novel component involved in chloroplast-to-nucleus retrograde signaling, an aspect that will be addressed in future studies.
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Claims 13
Claim · model-written summary
Arabidopsis double mutants were viable and indistinguishable from wild type under low light
- Taxon
- Arabidopsis thaliana
Arabidopsis thalianae0 - Material
- double mutantse1
- Treatment
- low light conditionse1
- Outcome
- viablee1
- Comparator
- wild typee1
Not reportedDirection
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“Arabidopsis thaliana double mutants strongly impaired”
e1“All double mutants were viable and indistinguishable from the wild type when grown under low light conditions”
Claim · model-written summary
Most double mutants developed a high chlorophyll fluorescence phenotype when grown in high light, except sex1-3/tpt-2
- Taxon
- Arabidopsis thalianaArabidopsis thalianae0
- Treatment
- high lighte2
- Outcome
- high chlorophyll fluorescence (HCF) phenotypee2
- Qualifier
- except for sex1-3/tpt-2e2
Not reportedComparatorDirection
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“Arabidopsis thaliana double mutants strongly impaired”
e2“except for sex1-3/tpt-2--developed a high chlorophyll fluorescence (HCF) phenotype and growth retardation when grown in high light”
Claim · model-written summary
Double mutants grown in high light showed growth retardation
- Taxon
- Arabidopsis thalianaArabidopsis thalianae0
- Treatment
- high lighte2
- Outcome
- growth retardatione2
- Direction
- decreaseinferrede2
- Qualifier
- except for sex1-3/tpt-2e2
Not reportedComparator
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“Arabidopsis thaliana double mutants strongly impaired”
e2“except for sex1-3/tpt-2--developed a high chlorophyll fluorescence (HCF) phenotype and growth retardation when grown in high light”
Claim · model-written summary
High chlorophyll fluorescence was linked to a specific decrease in plastome-encoded core proteins of both photosystems in the adg1-1/tpt-2 mutant
- Taxon
- Arabidopsis thalianaArabidopsis thalianae0
- Material
- adg1-1/tpt-2e3
- Outcome
- plastome-encoded core proteins of both photosystemse3
- Direction
- decreasee3
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“Arabidopsis thaliana double mutants strongly impaired”
e3“with the adg1-1/tpt-2 double mutant revealed that HCF was linked to a specific decrease in plastome-encoded core proteins of both photosystems”
Claim · model-written summary
Nuclear-encoded antennae (LHCs) accumulated normally in the high chlorophyll fluorescence mutants
- Taxon
- Arabidopsis thalianaArabidopsis thalianae0
- Outcome
- nuclear-encoded antennae (LHCs)e4
- Qualifier
- accumulated normallye4
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“Arabidopsis thaliana double mutants strongly impaired”
e4“nuclear-encoded antennae (LHCs) accumulated normally, but were predominantly not attached to their photosystems”
Claim · model-written summary
Antennae were predominantly not attached to their photosystems in the high chlorophyll fluorescence mutants
- Taxon
- Arabidopsis thalianaArabidopsis thalianae0
- Outcome
- attached to their photosystemse4
- Qualifier
- predominantly note4
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“Arabidopsis thaliana double mutants strongly impaired”
e4“nuclear-encoded antennae (LHCs) accumulated normally, but were predominantly not attached to their photosystems”
Claim · model-written summary
Uncoupled antennae are the major cause of high chlorophyll fluorescence in dark-adapted plants
- Taxon
- Arabidopsis thalianaArabidopsis thalianae0
- Outcome
- HCF of dark-adapted plantse5
- Qualifier
- Uncoupled antennae are the major causee5
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“Arabidopsis thaliana double mutants strongly impaired”
e5“Uncoupled antennae are the major cause for HCF of dark-adapted plants”
Claim · model-written summary
Feeding sucrose or glucose to high light-grown adg1-1/tpt-2 plants rescued the high chlorophyll fluorescence and growth phenotypes
- Taxon
- Arabidopsis thalianaArabidopsis thalianae0
- Material
- adg1-1/tpt-2e6
- Treatment
- Feeding of sucrose or glucosee6
- Outcome
- HCF- and growth phenotypese6
- Direction
- rescuede6
Not reportedComparator
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“Arabidopsis thaliana double mutants strongly impaired”
e6“Feeding of sucrose or glucose to high light-grown adg1-1/tpt-2 plants rescued the HCF- and growth phenotypes”
Claim · model-written summary
Elevated sugar levels increased expression of GPT2
- Taxon
- Arabidopsis thalianaArabidopsis thalianae0
- Treatment
- Elevated sugar levelse7
- Gene
- glucose-6-phosphate/phosphate translocator2 (GPT2)e7
- Outcome
- expressione7
- Direction
- increaseinferrede7
Not reportedComparator
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“Arabidopsis thaliana double mutants strongly impaired”
e7“Elevated sugar levels induce the expression of the glucose-6-phosphate/phosphate translocator2 (GPT2)”
Claim · model-written summary
The triple mutant adg1-1/tpt-2/gpt2-1 showed the same rescue of the phenotype by sugar feeding as the adg1-1/tpt-2 double mutant
- Taxon
- Arabidopsis thalianaArabidopsis thalianae0
- Material
- adg1-1/tpt-2/gpt2-1e7
- Treatment
- sugar feedinge7
- Outcome
- rescue of the HCF- and growth phenotypee7
- Direction
- no_changeinferrede7
- Comparator
- adg1-1/tpt-2 double mutante7
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“Arabidopsis thaliana double mutants strongly impaired”
e7“A triple mutant with an additional defect in GPT2 (adg1-1/tpt-2/gpt2-1) exhibited an identical rescue of the HCF- and growth phenotype in response to sugar feeding as the adg1-1/tpt-2 double mutant”
Claim · model-written summary
The rescue by sugar feeding is independent of the sugar-triggered induction of GPT2
- Taxon
- Arabidopsis thalianaArabidopsis thalianae0
- Gene
- GPT2e6
- Outcome
- rescuee6
- Qualifier
- independent from the sugar-triggered induction of GPT2e6
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“Arabidopsis thaliana double mutants strongly impaired”
e6“indicating that this rescue is independent from the sugar-triggered induction of GPT2”
Claim · model-written summary
Cytosolic carbohydrate availability is proposed to modulate acclimation to high light
- Taxon
- Arabidopsis thalianaArabidopsis thalianae0
- Outcome
- acclimation to high lighte5
- Qualifier
- cytosolic carbohydrate availability modulatese5
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“Arabidopsis thaliana double mutants strongly impaired”
e5“We propose that cytosolic carbohydrate availability modulates acclimation to high light in A. thaliana”
Claim · model-written summary
Carbohydrates may be a novel component of chloroplast-to-nucleus retrograde signaling
- Taxon
- Arabidopsis thalianaArabidopsis thalianae0
- Compound
- carbohydratese4
- Outcome
- retrograde signalinge4
- Qualifier
- chloroplast-to-nucleuse4
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“Arabidopsis thaliana double mutants strongly impaired”
e4“carbohydrates may be considered as a novel component involved in chloroplast-to-nucleus retrograde signaling”
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