Small Auxin Up RNA 56 (SAUR56) regulates heading date in rice

Abstract Heading date is one of the most important agronomic traits and a fundamental factor determining crop yield. Although many genes related to heading date have been reported in rice, the molecular mechanism of heading date is still poorly understood. The Small Auxin-Up RNA (SAUR) family genes regulate many aspects of plant growth and development. However, their functions involved in heading date of rice (Oryza sativa L.) are not characterized. Here, OsSAUR56 gene was edited by the CRISPR/Cas9 technology in the japonica cultivar Zhonghua11 (ZH11). We found that loss-of-function of OsSAUR56 led to early heading phenotype regardless of day length. OsSAUR56 was mainly expressed in anther, and its protein was localized in the cytoplasm and the nucleus. Gene expression analysis with quantitative RT-PCR showed that OsSAUR56 regulated flowering time and heading date by affecting the expression of a clock gene OsGI and two repressors, HEADING DATE 7 (Ghd7) and DTH8 (Ghd8/LHD1). Moreover, evolutionary analysis showed that OsSAUR56 presents divergence between indica and japonica, showing natural selection during the domestication of cultivated rice. These results indicate that OsSAUR56 plays an important role in the regulation of heading date, and may be an important target for rice breeding programs.