New insights into the regulation of greening and carbon-nitrogen balance by sugar metabolism through a plastidic invertase.

Since the photosynthetic apparatus of plants contains a massive amount of nitrogen, the regulation of its development by sugar signals is important to the maintenance of the carbon-nitrogen balance. Recently, we isolated a new Arabidopsis mutant, sicy (sugar-inducible cotyledon yellow)-192, whose cotyledons were prevented from greening by treatment with sucrose. On treatment with sucrose, the expression of photosynthesis- and nitrogen assimilation-related genes was respectively weaker and stronger in the mutant seedlings than the wild-type seedlings. In the mutants, the gene encoding plastidic alkaline/neutral (A/N) invertase (INV-E) was point-mutated at codon 294, with Tyr substituted for Cys (C294Y). These findings provide new insights into the regulation of greening and carbon-nitrogen balance by sugar metabolism through INV-E in plastids. In this addendum, we describe the phenotypes of sicy-192 on treatment with sucrose in more detail, and propose a possible relationship among sugar metabolism through INV-E, plastid-to-nucleus retrograde signaling, and ethylene, a plant hormone, in the regulation of plant development and metabolism.