Rice (Oryza sativa L.) is one of the leading food crops in the world. Its grain yield is mainly influenced by effective tiller number, grain number per panicle, and grain weight. Grain size, as a key factor determining grain weight, is a crucial agronomic trait related to grain yield in rice. Auxin, a plant hormone, serves as a vital regulator in almost all aspects in plant growth and development. However, the regulatory mechanism of auxin on rice grain size is inadequately understood.

Recently, a novel miR167a-OsARF6-OsAUX3 module regulating grain length and weight in rice has been identified through joint research. The findings revealed the genetic and regulatory mechanism underlying rice grain size through auxin response pathway, and provided a new candidate gene for further increasing yield potential of rice and other cereal crops.

Members of the joint research team include researchers from China National Rice Research Institute (CNRRI) of the Chinese Academy of Agricultural Sciences (CAAS), Inner Mongolia University, Zhejiang University, Agricultural Genomics Institute at Shenzhen (AGIS) of CAAS, Institute of Genetics and Developmental Biology (IGDB) of the Chinese Academy of Sciences (CAS), and the University of Fribourg, Switzerland.

Their previous studies have delved into the control of rice grain size and weight, and cloned a series of regulatory genes (Zhang et al., PNAS, 2012; Hu et al., Molecular Plant, 2015; Wang et al., Nature Genetics, 2015; Duan et al., Molecular Plant, 2017; Lyu et al., Plant Cell, 2020; Ruan et al., New Phytologist, 2020). In this study, a quantitative trait locus qGL5 for grain length (GL) and grain weight (GW) was identified in recombinant inbred lines of 9311 and Nipponbare (NPB), and fine mapped to a candidate gene, OsAUX3. OsARF6, demonstrated as an upstream transcription factor of OsAUX3, was reported to directly bind to the auxin response element (AuxRE) of the OsAUX3 promotor and thereby alter longitudinal expansion and auxin distribution/content in glume cells. OsARF6 was found to interact with OsIAA8 and OsIAA20 both involved in the auxin pathway. Besides, miR167a was confirmed to positively regulate GL and GW by directing OsARF6 mRNA silencing.

The project was funded by grants from the National Key Research and Development Program of China (2016YFD0100400), the National Natural Science Foundation of China (32060451) and the ZheJiang Provincial Natural Science Foundation of China (grant no. LZ19C020001).

A proposed model for the miR167a-OsARF6-OsAUX3 module regulating grain length and weight in rice

By Shen Huizhi (shenhuizhi@caas.cn)