Functional characterization of DiMMS21, a SUMO ligase from Desmodium intortum

Small ubiquitin-like modifiers E3 ligases in plant stress

Plants regularly encounter various environmental stresses such as salt, drought, cold, heat, heavy metals and pathogens, leading to changes in their proteome. Of these, a post-translational modification, SUMOylation is particularly significant for its extensive involvement in regulating various plant molecular processes to counteract these external stressors. Small ubiquitin-like modifiers (SUMO) protein modification significantly contributes to various plant functions, encompassing growth, development and response to environmental stresses. The SUMO system has a limited number of ligases even in fully sequenced plant genomes but SUMO E3 ligases are pivotal in recognising substrates during the process of SUMOylation. E3 ligases play pivotal roles in numerous biological and developmental processes in plants, including DNA repair, photomorphogenesis, phytohormone signalling and responses to abiotic and biotic stress. A considerable number of targets for E3 ligases are proteins implicated in reactions to abiotic and biotic stressors. This review sheds light on how plants respond to environmental stresses by focusing on recent findings on the role of SUMO E3 ligases, contributing to a better understanding of how plants react at a molecular level to such stressors.

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.