Light intensity affects chlorophyll synthesis during greening process by metabolite signal from mitochondrial alternative oxidase in Arabidopsis

Although mitochondrial alternative oxidase (AOX) has been proposed to play essential roles in high light stress tolerance, the effects of AOX on chlorophyll synthesis are unclear. Previous studies indicated that during greening, chlorophyll accumulation was largely delayed in plants whose mitochondrial cyanide-resistant respiration was inhibited by knocking out nuclear encoded AOX gene. Here, we showed that this delay of chlorophyll accumulation was more significant under high light condition. Inhibition of cyanide-resistant respiration was also accompanied by the increase of plastid NADPH/NADP(+) ratio, especially under high light treatment which subsequently blocked the import of multiple plastidial proteins, such as some components of the photosynthetic electron transport chain, the Calvin-Benson cycle enzymes and malate/oxaloacetate shuttle components. Overexpression of AOX1a rescued the aox1a mutant phenotype, including the chlorophyll accumulation during greening and plastidial protein import. It thus suggests that light intensity affects chlorophyll synthesis during greening process by a metabolic signal, the AOX-derived plastidial NADPH/NADP(+) ratio change. Further, our results thus revealed a molecular mechanism of chloroplast-mitochondria interactions.