Immunophilin CYN28 is required for accumulation of photosystem II and thylakoid FtsH protease in Chlamydomonas

Abstract

Excess light causes severe photodamage to photosystem II (PSII) where the primary charge separation for electron transfer takes place. Dissection of mechanisms underlying the PSII maintenance and repair cycle in green algae promotes the usage of genetic engineering and synthetic biology to improve photosynthesis and biomass production. In this study, we systematically analyzed the high light (HL) responsive immunophilin genes in Chlamydomonas (Chlamydomonas reinhardtii) and identified one chloroplast lumen-localized immunophilin, CYN28, as an essential player in HL tolerance. Lack of CYN28 caused HL hypersensitivity, severely reduced accumulation of PSII supercomplexes, and compromised PSII repair in cyn28. The thylakoid FtsH (filamentation temperature-sensitive H) is an essential AAA family metalloprotease involved in the degradation of photodamaged D1 during the PSII repair cycle and was identified as one potential target of CYN28. In the cyn28 mutant, the thylakoid FtsH undergoes inefficient turnover under HL condition. The CYN28-FtsH1/2 interaction relies on the FtsH N-terminal proline residues and is strengthened particularly under HL. Further analyses demonstrated CYN28 displays peptidyl-prolyl isomerase (PPIase) activity, which is necessary for its physiological function. Taken together, we propose that immunophilin CYN28 participates in PSII maintenance and regulates the homeostasis of FtsH under HL stress via its PPIase activity.

Advances in light system engineering across the phototrophic spectrum

“…A recent study published data on the immunophilin gene cyn28 , coding a protein designated CYN28, that is critical for high light acclimation in C. reinhardtii ( Fu et al., 2023 ). Immunophilins are widespread chaperones for ensuring proper protein folding.…”

The Role of FtsH Complexes in the Response to Abiotic Stress in Cyanobacteria

“…5 ). We cannot exclude a role of other protein factors like prolyl- cis - trans isomerases in the FtsH2/3 stability as immunophilin CYN28 with this activity is required for FtsH1/2 accumulation upon HL stress in Chlamydomonas ( Fu et al. 2023 ).…”