Small grain and semi-dwarf 3, a WRKY transcription factor, negatively regulates plant height and grain size by stabilizing SLR1 expression in rice

Key message OsWRKY36 represses plant height and grain size by inhibiting gibberellin signaling. Plant height and grain size are important agronomic traits affecting yield in cereals, including rice. Gibberellins (GAs) are plant hormones that promote plant growth and developmental processions such as stem elongation and grain size. WRKYs are transcription factors that regulate stress tolerance and plant development including height and grain size. However, the relationship between GA signaling and WRKY genes is still poorly understood. Here, we characterized asmall grain and semi-dwarf 3(sgsd3) mutant in rice cv. Hwayoung (WT). A T-DNA insertion in the 5 '-UTR ofOsWRKY36induced overexpression ofOsWRKY36in thesgsd3mutant, likely leading to the mutant phenotype. This was confirmed by the finding that overexpression ofOsWRKY36caused a similar small grain and semi-dwarf phenotype to thesgsd3mutant whereas knock down and knock out caused larger grain phenotypes. Thesgsd3mutant was also hyposensitive to GA and accumulated higher mRNA and protein levels ofSLR1(a GA signaling DELLA-like inhibitor) compared with the WT. Further assays showed that OsWRKY36 enhancedSLR1transcription by directly binding to its promoter. In addition, we found that OsWRKY36 can protect SLR1 from GA-mediated degradation. We thus identified a new GA signaling repressor OsWRKY36 that represses GA signaling through stabilizing the expression of SLR1.