Overexpression of OsSIN, encoding a novel small protein, causes short internodes in Oryza sativa

We report here the characterization of function of a novel gene, OsSIN (Orayza sativa SHORT INTERNODES). OsSIN with no intron, encodes a 106 amino acid polypeptide and has no homology proteins in GenBank. The gene shows predominant expression in shoots and is localized in the nucleus. Constitutive expression of OsSIN resulted in dwarfism and reduced number of inferior spikelets. The functional strength was correlated with the level of transgene expression. Transgenic plants were more insensitive to endogenous gibberellic acid (GA) levels than the wild type. The rice with OsSIN overexpression was less sensitive to GA than the wild type in terms of the second leaf sheath length. Expression of OsGAI at protein level was increased in OsSIN-overexpressed rice compared with the wild type. Our results suggest that OsSIN is a new member in the GA pathway regulating rice stem development.