Abstract

Grain size is a critical agronomic trait that influences grain yield in rice. However, the molecular mechanisms underlying grain size regulation in rice have not been fully elucidated. Here, we report that the GATA family transcription factor OsGATA1 is a novel regulator of grain size and weight. Loss-of-function of OsGATA1 leads to wide and heavy grains, whereas overexpression of OsGATA1 causes narrow and light grains. OsGATA1 regulates grain size by modulating cell proliferation in spikelet hulls. OsGATA1 is ubiquitously expressed in rice tissues, and its expression level increases with panicle development. The OsGATA1 protein localizes to both the nucleus and the cytoplasm and exhibits transcriptional activation activity. The screening of interacting proteins revealed that OsGATA1 interacts with GS9, a transcriptional activator involved in grain size regulation. Genetic analyses confirmed that OsGATA1 and GS9 function in a common genetic pathway to control grain size. In addition, haplotype analyses of OsGATA1 uncovered clear genetic divergence between indica and japonica subpopulations, and Hap2 and Hap3 may be superior haplotypes for grain weight improvement. Furthermore, loss-of-function of OsGATA1 results in increased expression of brassinosteroid (BR) biosynthetic genes and elevated levels of endogenous BRs, suggesting that OsGATA1 plays a role in regulating BR biosynthesis. Taken together, our findings reveal the roles of OsGATA1 in the regulation of grain size and BR biosynthesis and provide a new candidate gene for improving grain weight in rice.