Defects in leaf carbohydrate metabolism compromise acclimation to high light and lead to a high chlorophyll fluorescence phenotype in <it>Arabidopsis thaliana</it>

• Main Authors: Schmitz Jessica, Schöttler Mark, Krueger Stephan, Geimer Stefan, Schneider Anja, Kleine Tatjana, Leister Dario, Bell Kirsten, Flügge Ulf-Ingo, Häusler Rainer E
• Format: Article
• Language: English
• Published: BMC 2012-01-01
• Series: BMC Plant Biology
• Online Access: http://www.biomedcentral.com/1471-2229/12/8

<p>Abstract</p> <p>Background</p> <p>We have studied the impact of carbohydrate-starvation on the acclimation response to high light using <it>Arabidopsis thaliana </it>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; <it>tpt-2 </it>mutant) was crossed to mutants defective in (i) starch biosynthesis (<it>adg1-1, pgm1 </it>and <it>pgi1-1; </it>knock-outs of ADP-glucose pyrophosphorylase, plastidial phosphoglucomutase and phosphoglucose isomerase) or (ii) starch mobilization (<it>sex1-3</it>, knock-out of glucan water dikinase) as well as in (iii) maltose export from the chloroplast (<it>mex1-2</it>).</p> <p>Results</p> <p>All double mutants were viable and indistinguishable from the wild type when grown under low light conditions, but - except for <it>sex1-3/tpt-2 </it>- 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 <it>adg1-1/tpt-2 </it>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 <it>adg1-1/tpt-2 </it>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 (<it>adg1-1/tpt-2/gpt2-1</it>) exhibited an identical rescue of the HCF- and growth phenotype in response to sugar feeding as the <it>adg1-1/tpt-2 </it>double mutant, indicating that this rescue is independent from the sugar-triggered induction of GPT2.</p> <p>Conclusions</p> <p>We propose that cytosolic carbohydrate availability modulates acclimation to high light in <it>A. thaliana</it>. 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.</p>