摘要Oxidative post-translational modifications of specific chloroplast proteins contribute to the initiation of retrograde signaling.The Arabidopsis thaliana EXECUTER1(EX1)protein,a chloroplast-localized singlet oxygen(1O2)sensor,undergoes tryptophan(Trp)643 oxidation by 1O2,a chloroplast-derived and light-dependent reactive oxygen species.The indole side chain of Trp is vulnerable to 1O2,leading to the gener-ation of oxidized Trp variants and priming EX1 for degradation by a membrane-bound FtsH protease.The perception of 1O2 via Trp643 oxidation and subsequent EX1 proteolysis facilitate chloroplast-to-nucleus retrograde signaling.In this study,we discovered that the EX1-like protein EX2 also undergoes 1O2-depen-dent Trp530 oxidation and FtsH-dependent turnover,which attenuates 1O2 signaling by decelerating EX1-Trp643 oxidation and subsequent EX1 degradation.Consistent with this finding,the loss of EX2 function reinforces EX1-dependent retrograde signaling by accelerating EX1-Trp643 oxidation and subsequent EX1 proteolysis,whereas overexpression of EX2 produces molecular phenotypes opposite to those observed in the loss-of-function mutants of EX2.Intriguingly,phylogenetic analysis suggests that EX2 may have emerged evolutionarily to attenuate the sensitivity of EX1 toward 1O2.Collectively,these results suggest that EX2 functions as a negative regulator of the EX1 signalosome through its own 1O2-dependent oxidation,providing a new mechanistic insight into the regulation of EX1-mediated 1O2 signaling.