FAD-Linked Oxidoreductase Protein 1 (FLO1) Coordinates Grain Development and Drought Tolerance in Rice

Rice grain yield and drought tolerance are critical for global food security. So far, only a few genes have been reported to regulate both traits simultaneously. Here, we characterize OsFLO1, a previously unreported FAD-linked oxidoreductase, as a dual regulator of grain development and drought stress tolerance in rice. Genome-wide association studies (GWAS) revealed natural variation in OsFLO1, with haplotypes showing geographic adaptation to local rainfall. Functional analysis demonstrated that overexpression (OX) lines exhibited larger grains and improved panicle traits, while knockout (CR) lines showed reduced grain size and yield components despite increased tiller number. Regarding drought tolerance, OX lines of OsFLO1 enhanced drought tolerance, as evidenced by increased root length and antioxidant activities, whereas knockout (CR) lines displayed impaired stress responses. We further show that OsWRKY53 directly binds the OsFLO1 promoter, thereby activating its expression and coordinating both grain development and stress responses. Together, these results suggest that OsFLO1 functions as a key regulator coordinating grain development and drought tolerance, making it a promising target for improving rice productivity.