Far-red light-driven photoautotrophy of chlorophyll f-producing cyanobacterium without red-shifted phycobilisome core complex.

Chlorophyll (Chl) f production expands oxygenic photosynthesis of some cyanobacteria into the far-red light (FRL) region through reconstructed FRL-allophycocyanin (APC) cores and Chl f-containing photosystems. Presently, a unicellular cyanobacterium was isolated for studying FRL photoacclimation (FaRLiP) and classified as a new species Altericista leshanensis. It uses additional Chl f and FRL-APC cores, with retained white light (WL)-phycobiliproteins to thrive FRL conditions. Marker-less deletion of FaRLiP-apcE2 gene was constructed using CRISPR-Cpf1 system. This genetic manipulation has no significant effects on the expression of genes in the FaRLiP gene cluster, including adjacent apc genes under FRL conditions. The function-loss mutant cells cannot assemble FRL-APC cores, and show the decreased growth rate and Chl f production under FRL conditions. Interestingly, the expression levels of phycocyanin (PC) subunits (cpc) and photosystem II D1 proteins (psbA2) are significantly increased in mutant cells under FRL conditions. These results suggest that FRL acclimation in the mutant cells has a different photosynthetic apparatus due to the lack of FRL-APC cores. The alternative strategy of FaRLiP provides additional evidence of flexible pathways towards the potential application of Chl f and associated biotechnology.