On September 21st, the team of professor Jianmin Wan from Institute of Crop Science,  Chinese Academy of Agricultural Sciences, identified the key regulatory factor SMG4 for rice grain size and elucidated its molecular mechanism, providing new gene resources for rice grain type improvement. The related research results were published in the journal The Plant Cell.

Rice is an important food crop, and more than half of the population in China relies on rice as their staple food. Grain size is a major determinant of grain weight, directly affecting rice yield. Therefore, identifying key genes that regulate grain size and elucidating their molecular regulatory pathways can provide theoretical basis and gene resources for high-yield breeding of rice. The research team identified a small-grain mutant  smg4 in rice, in which the grain length, width, and thickness were all reduced. Compared with in the wild type, the number of cells in the smg4 mutant's glumes were smaller and fewer. Their study found that the SMG4 gene in the mutant had a mutation, which encodes a transporter protein of the MATE family. This protein can interact with COPII vesicle components and members of the cytochrome P450 subfamily CYP78A to jointly regulate the size of rice grains. The study reveals a new pathway for regulating rice grain size and provides new insights into the molecular and genetic mechanisms of rice grain size regulation.

Figure 1 A proposed working model for SMG4’s role in regulating rice grain size

By Ren Yulong (renyulong@caas.cn)