BIG regulates sugar response and C/N balance in Arabidopsis.

Mutations in BIG gene not only produce pleiotropic phenotypes of plant development but also impair plant adaptive responses under various stresses. However, the role of BIG gene in sugar signaling is not known. In this study, we first found that BIG deficiency significantly sensitized the sugar-induced anthocyanin accumulation and the sugar-inhibited primary root growth, suggesting BIG is an important component of the sugar signaling pathway. Then we found that big mutant plants had higher sugar levels compared with the wild type, indicating the involvement of BIG gene in regulating plant sugar homeostasis. Importantly, we also found that the relative ratio of carbon to nitrogen (C/N) was greatly enhanced by BIG deficiency. Overall, our work expands the known functionality of BIG and reveals its role in regulating sugar response and C/N balance. It is likely that BIG connects nutrient, light, and hormone signaling networks for regulating plant development and adaptive responses.