Arabidopsis CHLOROPHYLLASE 1 protects young leaves from long-term photodamage by facilitating FtsH-mediated D1 degradation in photosystem II repair

Abstract

The proteolytic degradation of the photodamaged D1 core subunit during the photosystem II (PSII) 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 PSII repair 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, whereas seedlings overexpressing CLH1 have enhanced light tolerance compared with the wild type. CLH1 is localized in the developing chloroplasts of young leaves and associates with the PSIIdismantling complexes RCC1 and RC47, with a preference for the latter upon exposure to high light. Furthermore, degradation of damaged D1 protein is retarded in young clh1-1/2-2 leaves after 18-h highlight exposure but is rescued by the addition of recombinant CLH1 in vitro. Moreover, overexpression of CLH1 in a variegated mutant (var2-2) that lacks 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. Taken together, these results establish CLH1 as a long-sought chlorophyll dephytylation enzyme that is involved in PSII repair and functions in long-term adaptation of young leaves to high-light exposure by facilitating FtsH-mediated D1 degradation.

Research Progress in the Interconversion, Turnover and Degradation of Chlorophyll

“…When photosystem (PS) damage occurs during stress conditions, PSII repair and Chl turnover subsequently occurs. A Chl turnover pathway is required for PSII repair and protection of young leaves from photodamage [7]. During leaf senescence or fruit maturation, Chl degradation is the major Chl metabolism direction.…”

Chlorophyllase, a Common Plant Hydrolase Enzyme with a Long History, Is Still a Puzzle

“…Considering that the amino acid sequences of CLHs are not very conserved across species and PPH is the core dephytylation enzyme during leaf senescence, but not during fruit ripening in tomato, it is possible that the function of CLHs varies in species or plant organs. Most recently, a report revealed additional information on CLHs [39,40]. It was found that Arabidopsis AtCLH1 was localized to the developing chloroplasts of young leaves but was located in the cytosol of mature leaves [39].…”

“…Most recently, a report revealed additional information on CLHs [39,40]. It was found that Arabidopsis AtCLH1 was localized to the developing chloroplasts of young leaves but was located in the cytosol of mature leaves [39]. Leaves from CLH1-null mutant seedlings Most recently, a report revealed additional information on CLHs [39,40].…”

“…It was found that Arabidopsis AtCLH1 was localized to the developing chloroplasts of young leaves but was located in the cytosol of mature leaves [39]. Leaves from CLH1-null mutant seedlings Most recently, a report revealed additional information on CLHs [39,40]. It was found that Arabidopsis AtCLH1 was localized to the developing chloroplasts of young leaves but was located in the cytosol of mature leaves [39].…”

“…Leaves from CLH1-null mutant seedlings Most recently, a report revealed additional information on CLHs [39,40]. It was found that Arabidopsis AtCLH1 was localized to the developing chloroplasts of young leaves but was located in the cytosol of mature leaves [39]. Leaves from CLH1-null mutant seedlings and those from CLH1-and CLH2-overexpression seedlings were ~25% lower and ~30% higher Chl contents, respectively.…”