OsBRXL4 Regulates Shoot Gravitropism and Rice Tiller Angle through Affecting LAZY1 Nuclear Localization

Abstract Rice tiller angle is a key agronomic trait that contributes to ideal plant architecture and grain production. Our previous study showed that LAZY1 (LA1) controls tiller angle via affecting shoot gravitropism, but the molecular mechanism remains largely unknown. Here, we identified a LA1-interacting protein named Brevis Radix Like 4 (OsBRXL4). We showed that the interaction between OsBRXL4 and LA1 occurs at the plasma membrane and that their interaction determines LA1 nuclear localization. We found that LA1 nuclear localization is essential for LA1 function, which is different from AtLA1, the ortholog in Arabidopsis . Overexpression of OsBRXL4 leads to a prostrate growth phenotype, whereas OsBRXLs RNAi plants, in which the expression levels of OsBRXL1 , OsBRXL4 , and OsBRXL5 were decreased, display a compact phenotype. Further genetic evidence confirmed that OsBRXL4 controls rice tiller angle by affecting LA1 nuclear localization. Consistent with this, OsBRXL4 regulates the shoot gravitropism through affecting polar auxin transport as did LA1. Therefore, our study not only identifies OsBRXL4 as a regulatory component of rice tiller angle, but also provides a new insight into our understanding of rice plant architecture.