A Sucrose Non-Fermenting-1-related Protein Kinase 1 Gene from Wheat, TaSnRK1α Regulates Starch Biosynthesis by Modulating AGPase Activity

Major portion of wheat grain consist of carbohydrate, mainly starch. The proportion of amylose and amylopectin in starch greatly influence the end product quality. Advancement in understanding starch biosynthesis pathway and modulating key genes has enabled the genetic modification of crops resulting in enhanced starch quality. However, the regulation of starch biosynthesis genes still remains unexplored. So, to expand the limited knowledge, here, we characterized a Ser/Thr kinase, SnRK1 alpha in wheat and determined its role in regulating starch biosynthesis. SnRK1 is an evolutionary conserved protein kinase and share homology to yeast SNF1. Yeast complementation assay suggests TaSnRK1 alpha restores growth defect and promotes glycogen accumulation. Domain analysis and complementation assay with truncated domain proteins suggest the importance of ATP-binding and UBA domain in TaSnRK1 alpha activity. Sub-cellular localization identified nuclear and cytoplasmic localization of TaSnRK1 alpha in tobacco leaves. Further, heterologous over-expression (O/E) of TaSnRK1 alpha in Arabidopsis not only led to increase in starch content but also enlarges the starch granules. TaSnRK1 alpha was found to restore starch accumulation in Arabidopsis kin10. Remarkably, TaSnRK1 alpha O/E increases the AGPase activity suggesting the direct regulation of rate limiting enzyme AGPase involved in starch biosynthesis. Furthermore, in vitro and in vivo interaction assay reveal that TaSnRK1 alpha interacts with AGPase large sub-unit. Overall, our findings indicate that TaSnRK1 alpha plays a role in starch biosynthesis by regulating AGPase activity.