Regulation of the Carbon and Nitrogen Balance by a Plastidic Invertase in Arabidopsis

Abstract

Since the photosynthetic apparatus contains a massive amount of nitrogen in plants, the regulation of its development by sugar signals is important to the maintenance of the carbon-nitrogen balance. Here, we isolated an Arabidopsis mutant (sicy-192) whose cotyledon greening was inhibited by treatments with sugars, such as sucrose, glucose, and fructose. In the mutant, the gene encoding plastidic alkaline/neutral (A/N) invertase (INV-E) was point-mutated at codon 294, with Tyr substituted for Cys (C294Y). Interestingly, the greening of cotyledons in the knockout-INV-E lines was not inhibited by treatment with the sugars. The mutant INV-E was more stable than the wild-type INV-E. On treatment with sucrose, the expression of photosynthesis-related genes was weaker in seedlings of mutant plants than wild-type seedlings, while the activity of nitrate reductase was stronger in the mutant plants than wild-type plants. These findings suggest that Cys294 of INV-E is associated with the development of the photosynthetic apparatus and the assimilation of nitrogen in Arabidopsis seedlings to control the ratio of sucrose content to hexose content. The transcript and protein levels of plastid-encoded genes were lower in the sicy-192 mutants than the wild-type plants, suggesting that sugar metabolism through INV-E promotes plastid signaling to regulate the carbon-nitrogen balance.