GW4 is regulated by GS2 to control grain width in rice

Grain width is one of the important factors determining grain yield and appearance quality. However, the genetic and molecular mechanisms controlling grain width remain be largely unexplored. In this study, we characterized a grain width mutant gw4 (grain width on chromosome 4), which showed reduced grain width but did not affect grain length. Sequence analysis revealed that a single base substitution (G to A) of LOC_Os04g01590 in gw4 resulted in the conversion of original encoded glycine to aspartate. The gene encodes an arginase that is localized on the mitochondrial and is highly expressed in panicles. RNA-seq and expression analysis showed that gw4 can control glume width by regulating the expression of cell cycle and cell expansion genes. Additionally, we also found that GS2 acts upstream of GW4 and regulates its expression by directly binding to GW4 promoter. In conclusion, we revealed that GW4 plays an important role in maintaining rice grain development. These results provide new insight into the genetic mechanism of arginase in the control of grain width and provide a potential target for molecular breeding of grain size.