Ya-Nan Tian 
Rui-Hao Zhong 
Jun-Bin Wei 
Hong-Hui Luo 
Yoram Eyal 
Hong-Lei Jin 
La-Jie Wu 
Ke-Ying Liang 
Ying-Man Li 
Shu-Zhen Chen
Zhao-Qi Zhang 
Xue-Qun Pang

The proteolytic degradation of the photodamaged D1 core subunit during photosystem (PS) II repair cycle is well understood, but chlorophyll turnover during D1 degradation remains unclear. Here, we report that Arabidopsis thaliana CHLOROPHYLLASE 1 (CLH1) plays important roles in the process. The abundance of CLH1 and CLH2 peaks in young leaves and is induced by high-light exposure. Seedlings of clh1 single and clh1-1/2-2 double mutants display increased photoinhibition after long-term high-light exposure, while seedlings overexpressing CLH1 have enhanced light tolerance, compared to the wild type. CLH1 localizes in the developing chloroplasts of young leaves and associates with PSII-dismantling complexes, RCC1 and RC47, with preference for the latter upon high-light. Furthermore, degradation of damaged D1 protein is retarded in clh1-1/2-2 young leaves after 18-h high-light exposure, but rescued by addition of recombinant CLH1 in vitro. Moreover, overexpressing CLH1 in a variegated mutant (var2-2) lacking thylakoid protease FtsH2, with which CLH1 interacts, suppresses the variegation and restores D1 degradation. A var2-2 clh1-1/2-2 triple mutant shows more severe variegation and seedling death. These results establish CLH1 as a long-sought chlorophyll dephytylation enzyme involved in PSII repair, functioning in long-term adaptation of young leaves to high-light exposure by facilitating FtsH-mediated D1 degradation.