A SUMO ligase OsMMS21 regulates rice development and auxin response.

SUMOylation, which transfers the Small Ubiquitin-related Modifier (SUMO) polypeptides to target proteins, regulates diverse cellular processes in eukaryotes. The SUMO conjugation reaction is usually promoted by SUMO E3 ligases, but the molecular functions of this type of enzymes remain unclear in cereal crops. Here, OsMMS21, a SUMO E3 ligase, was functionally characterized in rice (Oryza sativa). Bioinformatics analysis showed that OsMMS21 harbors a conserved SP-RING domain that is essential for the activity of SUMO ligases. Biochemical data indicated that this protein is auto-SUMOylated. Besides, overexpression of OsMMS21 rescued the developmental defects of the AtMMS21 mutant, supporting that OsMMS21 is a functional homolog of the Arabidopsis SUMO ligase AtMMS21. The OsMMS21 rice T-DNA mutant displays a short-root and dwarfism phenotype. RNA-seq data revealed that the expression levels of many genes involved in signaling transduction of hormones, including auxin, are altered in the OsMMS21 mutant. Further results under the auxin treatment showed that the OsMMS21 mutant is insensitive to auxin. Collectively, our results demonstrated the molecular features of OsMMS21 and uncovered the roles of this SUMO ligase in development and auxin response, providing hints for further studies on protein SUMOylation in rice.