BIG Gene Regulates Sugar Signaling And C/N Ratio In Arabidopsis

Sugar molecules including glucose and sucrose produced by photosynthesis are used both as building blocks for various cellular components and as energy source for life,as well as signaling molecules not only to activate downstream receptors and modulate the expression of targeted genes,but also to interact with many other signaling pathways in regulating plant growth,development and adaptive response.Accumulating evidence shows that the network architecture and organization of sugar signaling pathways are extremely complicated and tightly regulated.BIG is a functionally conserved gene,required for auxin transport.Mutations in BIG gene result in pleiotropic developmental defects in root,inflorescence and silique as well as impair plant response to light and many plant hormones,including gibberellin,ethylene,and jasmonic acid.However,the role of BIG gene in the sugar signaling is not known.In this study,we first found that BIG gene mutants exhibit a more sensitiveness to sugar-inhibited primary root and hypocotyl elongation.BIG deficiency significantly potentiates the sugar-induced anthocyanin accumulation and the sugar-inhibited seed germination,suggesting BIG gene might be an important component of the sugar signaling pathway.This suggestion was borne out when the sugar contents were measured.The mutant plants had higher levels of the endogenous sugar compared to the wild-type,indicating mutations in BIG gene perturbed the cellular sugar homeostasis.Furthermore,we investigated the possibility that BIG gene is indispensable for maintaining nutritional balance in plant,and found that the relative ratio of carbon and nitrogen was greatly enhanced by BIG disruption that has been well documented to be important in plant defence.This fits well with the results when herbivorous aphids(M.persicae)were tested for their feeding preference and a strong feeding repelling effect of BIG mutation was observed although the underlying molecular mechanism remains to be defined.In summary,the current study reveals a regulatory role of BIG gene in sugar signaling and C/N balance in Arabidopsis.