FLOURY ENDOSPERM12 Encoding Alanine Aminotransferase 1 Regulates Carbon and Nitrogen Metabolism in Rice

Starch is a major storage substance in cereal grains, and starch biosynthesis is a complex process. In order to elucidate regulation of the starch biosynthesis pathway, we screened a series of rice (Oryza sativa L.) endosperm mutants. In this study, we identified a floury white-core endosperm mutant named floury endosperm12 (flo12). The flo12 mutant exhibited loosely packed starch granules and a lower thousand kernel weight compared to wild type. Semithin sections revealed that compound starch grains (SG) in flo12 interior endosperm cells were developed abnormally. Furthermore, amylose content was decreased, while total protein content was significantly increased in flo12 grains. Map-based cloning showed that FLO12 encodes rice alanine aminotransferase 1 (OsAlaAT1). OsAlaAT1 is highly expressed in developing endosperm. Subcellular localization showed that OsAlaAT1 is localized in the cytosol. Moreover, the expression of most starch synthesis-related genes was decreased, while most of the storage protein coding genes had elevated expression levels in the flo12 mutant. In addition, overexpression of the OsAlaAT1 gene increased grain weight. In brief, we demonstrated that OsAlaAT1 regulates carbon and nitrogen metabolism, which provides a new insight for the improvement of rice quality and yield.