Wide grain 4, encoding an alpha-tubulin, regulates grain size by affecting cell expansion in rice

Rice is one of the three most important food crops in the world. Increasing rice yield is an effective way to ensure food security. Grain size is a key factor affecting rice yield; however, the genetic and molecular mechanisms regulating grain size have not been fully investigated. In this study, we identified a rice mutant, wide grain 4-D (wg4-D), that exhibited a significant increase in grain width and a decrease in grain length. Histological analysis demonstrated that WG4 affects cell expansion thereby regulating grain size. MutMap-based gene mapping and complementary transgenic experiments revealed that WG4 encodes an alpha-tubulin, OsTubA1. A SNP mutation in WG4 affected the arrangement of cortical microtubules and caused a wide-grain phenotype. WG4 is located in nuclei and cytoplasm and expressed in various tissues. Our results provide insights into the function of tubulin in rice and identifies novel targets the regulation of grain size in crop breeding.