Photosystem II monomeric antenna CP26 has a key role in Non-Photochemical Quenching inChlamydomonas reinhardtii

Abstract

SUMMARYThermal dissipation of the excitation energy harvested in excess, named non-photochemical quenching (NPQ), is one of the main photoprotective mechanisms evolved in oxygenic photosynthetic organisms. Here, the specific function in photoprotection and light harvesting of the monomeric Photosystem II antenna CP26, was investigated inChlamydomonas, model organism for green algaeCRISPR/Cas9 genome editing and complementation strategies were applied to generate newcp26knock-out mutants (namedk6#) that differently from previous findings, did not negatively affected CP29 accumulation, allowing to compare mutants specifically deprived of CP26, CP29 or bothThe absence of CP26 partially affected Photosystem II activity causing a reduced growth at low or medium light but not at high irradiances. However, the main phenotype observed in k6# mutants was a more than 70% reduction of NPQ compared to wild-type. This NPQ phenotype could be fully rescued by genetic complementation demonstrating that ∼50% of CP26 content compared to wild-type was sufficient to restore the NPQ capacity.Our findings demonstrate a pivotal role for CP26 in NPQ induction while CP29 has a crucial function for Photosystem II activity. The genetic engineering of these two proteins could be a promising strategy to regulate photosynthetic efficiency of microalgae under different light regimes.