Photosystem II (PSII) repair is a fundamental physiological process governing the resilience of photosynthetic organisms against high light (HL) stress. A recent study by Yao et al. (2025) provides significant mechanistic insights into this process within the model green alga Chlamydomonas reinhardtii. The authors characterize the lumenal immunophilin CYN38, a homolog of the Arabidopsis CYP38, identifying it as a critical auxiliary protein for the biogenesis and stabilization of PSII. Through the characterization of a unique insertion mutant, cyn38, which produces a C-terminally extended protein, the study elucidates that homodimerization of CYN38—mediated by its C-terminus—is a prerequi... More >