Loss of carbonic anhydrase in the thylakoid lumen causes unusual moderate-light-induced rearrangement of the chloroplast in Chlamydomonas reinhardtii as a way of photosystem II photoprotection

Abstract

Chlamydomonas reinhardtii cells have a single large cup-shaped chloroplast that can lose lobes under high light to prevent photodamage of the photosynthetic apparatus, including photosystem II (PSII). Here, under moderate light treatment, the development of the unusual morphology of the chloroplast is shown for mutant cia3, which is deficient in carbonic anhydrase (EC 4.2.1.1) CAH3 in the thylakoid lumen, while such light intensity is harmless for wild type (WT) cells for hours. Cia3 cells had more activated PSII photoprotective mechanisms and showed a tendency to shift in the balance of the PSII damage-repair cycle, whereas PSII retained the same photosynthetic efficiency as in the WT. These findings allow speculation about the unique PSII photoprotection strategy by rearranging the chloroplast in the absence of CAH3. CAH3, in turn, is suggested to be an important participant of the C. reinhardtii photosynthetic apparatus operation, functioning in close connection with PSII.