Brassinosteroid regulation in rice seed biology

Rice ( Oryza sativa L.) is not only a model monocotyledon plant, but also an important cereal seed crop. Improvements in seed-related traits is the key to obtaining high grain yield and quality, therefore attracting attention from both scientists and crop breeders. In higher plants, brassinosteroid (BR), a major growth-promoting hormone, plays an important role in regulating numerous agronomic traits associated with both vegetative and reproductive growth, thereby presenting huge application potential. Here, we review recent progress into BR regulation in rice seed biology. Both BR biosynthesis and signaling have been shown to regulate grain size, grain filling, grain number, seed germination and biosynthesis of seed components. Thus, considering the pleiotropic effects of BR, strategies aimed at genetic modulation of the BR pathway have been proposed to improve seed-related traits in rice, and therefore, enhance both yield and quality. This review not only strengthens our understanding of the underlying mechanism and regulatory network of BR-regulated key agronomic traits in rice, but also facilitates the future application of BR in rice breeding programs.