Functions of OsWRKY24, OsWRKY70 and OsWRKY53 in regulating grain size in rice.

OsWRKY24 functions redundantly with OsWRKY53, while OsWRKY70 functions differently from OsWRKY53 in regulating grain size. Grain size is a key agronomic trait that affects grain yield and quality in rice (Oryza sativa L.). The transcription factor OsWRKY53 positively regulates grain size through brassinosteroid (BR) signaling and Mitogen-Activated Protein Kinase (MAPK) cascades. However, whether the OsWRKY53 homologs OsWRKY24 and OsWRKY70 also contribute to grain size which remains unknown. Here, we report that grain size in OsWRKY24 overexpression lines and oswrky24 mutants is similar to that of the wild type. However, the oswrky24 oswrky53 double mutant produced smaller grains than the oswrky53 single mutant, indicating functional redundancy between OsWRKY24 and OsWRKY53. In addition, OsWRKY70 overexpression lines displayed an enlarged leaf angle, reduced plant height, longer grains, and higher BR sensitivity, phenotypes similar to those of OsWRKY53 overexpression lines. Importantly, a systematic characterization of seed length in the oswrky70 single, the oswrky53 oswrky70 double and the oswrky24 oswrky53 oswrky70 triple mutant indicated that loss of OsWRKY70 also leads to increased seed length, suggesting that OsWRKY70 might play a role distinct from that of OsWRKY53 in regulating grain size. Taken together, these findings suggest that OsWRKY24 and OsWRKY70 regulate rice grain size redundantly and independently from OsWRKY53.