Mutation of RGG2, which encodes a type B heterotrimeric G protein γ subunit, increases grain size and yield production in rice

Summary Heterotrimeric G proteins, which consist of G α , G β and G γ subunits, function as molecular switches that regulate a wide range of developmental processes in plants. In this study, we characterised the function of rice RGG 2 , which encodes a type B G γ subunit, in regulating grain size and yield production. The expression levels of RGG 2 were significantly higher than those of other rice G γ ‐encoding genes in all tissues tested, suggesting that RGG 2 plays essential roles in rice growth and development. By regulating cell expansion, overexpression of RGG2 in Nipponbare ( NIP ) led to reduced plant height and decreased grain size. By contrast, two mutants generated by the clustered, regularly interspaced, short palindromic repeat ( CRISPR )/CRISPR‐associated protein 9 (Cas9) system in the Zhenshan 97 ( ZS 97) background, zrgg2‐1 and zrgg2‐2 , exhibited enhanced growth, including elongated internodes, increased 1000‐grain weight and plant biomass and enhanced grain yield per plant (+11.8% and 16.0%, respectively). These results demonstrate that RGG 2 acts as a negative regulator of plant growth and organ size in rice. By measuring the length of the second leaf sheath after gibberellin ( GA 3 ) treatment and the GA ‐induced α‐amylase activity of seeds, we found that RGG 2 is also involved in GA signalling. In summary, we propose that RGG 2 may regulate grain and organ size via the GA pathway and that manipulation of RGG 2 may provide a novel strategy for rice grain yield enhancement.