Complex lumenal immunophilin AtCYP38 influences thylakoid remodelling in Arabidopsis thaliana.

Investigations of the luminal immunophilin AtCYP38 (cyclophilin 38) in Arabidopsis thaliana (At), the orthologue of the complex immunophilin TLP40 from Spinacia oleracea, revealed its involvement in photosystem II (PSII) repair and assembly, biogenesis of PSII complex, and cellular signalling. However, the main physiological roles of AtCYP38 and TLP40 are related to regulation of thylakoid PP2A-type phosphatase involved in PSII core protein dephosphorylation, and chaperone function during protein folding. Here we further investigate physiological roles of AtCYP38 and analyse the ultrastructure of chloroplasts from cyp38-2 plants. Transmission electron microscopy followed by quantitative micrography revealed modifications in thylakoid stacking. We also confirm that the depletion of AtCYP38 influences PSII performance, which leads to stunted phenotype of cyp38-2 plants.