Arabidopsis MKKK20 is involved in osmotic stress response via regulation of MPK6 activity.

Plants have developed various regulatory pathways to adapt to environmental stresses. In this study, we identified Arabidopsis MKKK20 as a regulator in the response to osmotic stress. mkkk20 mutants were found to be sensitive to high concentration of salt and showed higher water loss rates than wild-type (WT) plants under dehydration conditions. In addition, mkkk20 mutants showed higher accumulation of superoxide, a reactive oxygen species (ROS), compared to WT plants under high salt condition. In contrast, transgenic plants overexpressing MKKK20 displayed tolerance to salt stress. MKKK20 transcripts were increased by the treatments with NaCl, mannitol, MV, sorbitol, and cold, suggesting that MKKK20 is involved in the response to osmotic, ROS, and cold stresses. In-gel kinase assay showed that MKKK20 regulates the activity of MPK6 under NaCl, cold, and H(2)O(2) treatments. Taken together, our results suggest that MKKK20 might be involved in the response to various abiotic stresses, especially osmotic stress, through its regulation of MPK6 activity.