Arabidopsis RING-type E3 ubiquitin ligase XBAT35.2 promotes proteasome-dependent degradation of ACD11 to attenuate abiotic stress tolerance.

Plants employ multiple mechanisms to cope with a constantly changing and challenging environment including utilizing the ubiquitin proteasome system (UPS) to alter their proteome to assist in initiating, modulating and terminating responses to stress. We previously reported that the ubiquitin ligase XBAT35.2 mediates the proteasome-dependent degradation of Accelerated Cell Death 11 (ACD11) to promote pathogen defense. Here, we demonstrate roles for XBAT35.2 and ACD11 in abiotic stress tolerance. Similar to pathogen infection, abiotic stress stabilizes XBAT35.2 and protein abundance rose consistently with increasing concentrations of abscisic acid (ABA) and salt. Surprisingly, exposure to ABA and salt increased ACD11 stability and overexpression of ACD11 improves survival of salt and drought stress, suggesting a role for ACD11 in promoting tolerance. However, prolonged exposure to high concentrations of ABA/salt resulted in ubiquitination and proteasome-dependent degradation of ACD11. The stress-induced turnover of ACD11 requires XBAT35.2 as degradation is slowed in the absence of the E3 ubiquitin ligase. Consistent with XBAT35.2 mediating the proteasome-dependent degradation of ACD11, loss of E3 ubiquitin ligase function enhances tolerance of salt and drought stress, while overexpression increases sensitivity. A model is presented where upon abiotic stress, ACD11 abundance increases to promote tolerance. Meanwhile, XBAT35.2 accumulates and in turn promotes the degradation of ACD11 to attenuate the stress response. The results characterize XBAT35.2 as an E3 ubiquitin ligase with opposing roles in abiotic and biotic stress. Supporting Information.