SUMOylation of MYB30 enhances salt tolerance by elevating alternative respiration via transcriptionally upregulating AOX1a in Arabidopsis

Salt stress reduces crop growth and productivity globally. Here we report that a R2R3-MYB transcription factor MYB30 participates in salt tolerance in Arabidopsis. MYB30 can be SUMOylated by SIZ1 in response to salt stress and the lysine (K)283 of MYB30 is essential for its SUMOylation. In contrast to wild-type MYB30, the MYB30(K283R) mutant failed to rescue the salt-sensitive phenotype of the myb30-2 mutant, indicating that SUMOylation of MYB30 is required for the salt-stress response. Through transcriptomic analysis, we identified a MYB30 target, alternative oxidase 1a (AOX1a). MYB30 binds the promoter of AOX1a and upregulates its expression in response to salt stress; however, MYB30(K283R) cannot bind the promoter of AOX1a. The cyanide (CN)-resistant alternative respiration (Alt) mediated by AOX is significantly reduced in the myb30-2 mutant through the loss of function of MYB30. As a result, the redox homeostasis is disrupted in the myb30-2 mutant compared with that in wild-type seedlings (WT) under salt conditions. The artificial elimination of excess reactive oxygen species partially rescues the salt-sensitive phenotype of the myb30-2 mutant, whereas after the exogenous application of SHAM, an inhibitor of AOXs and Alt respiration, the salt tolerance of Col-0 and the complemented plants decreased to a level similar to that observed in myb30-2. Finally, overexpression of AOX1a in myb30-2 confers WT-like salt tolerance compared with that of the myb30-2 mutant. Taken together, our results revealed a functional link between MYB30 and AOX1a, and indicated that SIZ1-mediated SUMOylation of MYB30 enhances salt tolerance by regulating Alt respiration and cellular redox homeostasis via AOX1a in Arabidopsis.