Abstract
Environmental information perceived by chloroplasts can be translated into retrograde signals that alter the expression of nuclear genes. Singlet oxygen (1O2) generated by photosystem II (PSII) can cause photo-oxidative damage of PSII but has also been implicated in retrograde signaling. We previously reported that a nuclear-encoded chloroplast FtsH2 metalloprotease coordinates 1O2-triggered retrograde signaling by promoting the degradation of the EXECUTER1 (EX1) protein, a putative 1O2 sensor. Here, we show that a 1O2-mediated oxidative post-translational modification of EX1 is essential for initiating 1O2-derived signaling. Specifically, the Trp643 residue in DUF3506 domain of EX1 is prone to oxidation by 1O2. Both the substitution of Trp643 with 1O2-insensitive amino acids and the deletion of the DUF3506 domain abolish the EX1-mediated 1O2 signaling. We thus provide mechanistic insight into how EX1 senses 1O2 via Trp643 located in the DUF3506 domain.