Global studies of miR021b function in wheat

Seed germination is not only a critical developmental step in the wheat life cycle, but is also important for agricultural production including yield and quality. However, in wheat, the knowledge of the mechanism of regulating seed germination is still limited. In this study, we found 22nt microRNA (miR) miR021b, specifically expressed in scutellum of developing and germinating wheat seed, generated phased ta-siRNAs by cleaving a long non coding RNA LNCR. Overexpression of miR021b in wheat showed a retarded germination and improved resistance to pre-harvest sprouting (PHS), while its silencing enhanced germination rate through transiently expressing in immature embryos. To figure out the mechanism of miR021b regulating seed germination, we found miR021b affected the expression of genes involved in bioactive gibberellin (GA) synthesis and its overexpression reduced the bioactive GA content and inhibited amylase genes expression. In addition, it was observed that TaVp1, TaABF and TaABI3, responded the abscisic acid (ABA) signaling, can bind the promoter of miR021b precursor and regulated its expression, suggesting that miR021b might function in GA-ABA balance during germination. This study identified a signaling pathway that miR021b controlled GA-dependent seed germination in wheat through generating phased ta-siRNAs by cleaved a long non coding RNA LNCR.