Rice transcription factor OsDOF18 enlarges the starch granule size by cytokinin

Abstract

Nitrogen is an essential element for rice biomass and starch quality. However, the molecular mechanism affecting starch characteristic by nitrogen remains poorly defined. Previously, we noted that Oryza sativa DNA BINDING WITH ONE FINGER 18 (OsDOF18) mediated ammonium transport by ammonium transporters. Here, we found that OsDOF18 induced nitrogen accumulation in seed. By analyzing the osdof18 mutant and OsDOF18 overexpression transgenic seed, OsDOF18 inhibited small size, granule formation of starch, but induced large size starch granules and apparent amylose content. By transcriptome analysis and qRT-PCR in OsDOF18 mutant plants, OsDOF18 affected the transcription level of cytokinin metabolism-related genes. We further found that the content of cytokinin- zeatin and trans-zeatin-riboside was reduced in the osdof18 mutant. By analyzing the Cytokinin-related transgenic lines-VIN3-LIKE 2(OsVIL2)-OX (increased endogenous cytokinin content), Oryza sativa A-type response regulator (OsRR1)-OX (cytokinin signaling pathway Type A response factor) and Early heading date 1 (Ehd1)-OX (cytokinin signaling pathway Type B response factor), we found that cytokinin content and signaling enhanced lines had more large size granules, but less small size granules, which is similar with the OsDOF18 overexpression lines. These results demonstrated that OsDOF18 affected starch granule size by cytokinin at a physiological and genetic level, and provides new insight that OsDOF18 coordinated with carbon and nitrogen metabolism in rice development.