1. EXECUTER2 modulates the EXECUTER1 signalosome through its singlet oxygen-dependent oxidation.
- Author
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Dogra, Vivek, Singh, Rahul Mohan, Li, Mengping, Li, Mingyue, Singh, Somesh, and Kim, Chanhong
- Abstract
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 (
1 O 2) sensor, undergoes tryptophan (Trp) 643 oxidation by1 O 2 , a chloroplast-derived and light-dependent reactive oxygen species. The indole side chain of Trp is vulnerable to1 O 2 , leading to the generation of oxidized Trp variants and priming EX1 for degradation by a membrane-bound FtsH protease. The perception of1 O 2 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 undergoes1 O 2 -dependent Trp530 oxidation and FtsH-dependent turnover, which attenuates1 O 2 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 toward1 O 2. Collectively, these results suggest that EX2 functions as a negative regulator of the EX1 signalosome through its own1 O 2 -dependent oxidation, providing a new mechanistic insight into the regulation of EX1-mediated1 O 2 signaling. EXECUTER1 (EX1) and EX2 proteins have long been considered major players in mediating singlet oxygen (1 O 2)-triggered chloroplast-to-nucleus retrograde signaling, but the specific mechanisms by which they regulate1 O 2 signaling have been unclear. This study demonstrates that the1 O 2 -driven oxidative modification of EX2 modulates EX1-mediated1 O 2 signaling by hindering the oxidation of EX1 that is essential for the initiation of1 O 2 signaling. [ABSTRACT FROM AUTHOR]- Published
- 2022
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