Studies of CrHCF244 reveal similarities and differences in psbA translation between Chlamydomonas reinhardtii and Arabidopsis thaliana

Translation of psbA, the chloroplast gene that encodes the D1 subunit of Photosystem II (PSII), is important for both PSII biogenesis and repair. The translation of the psbA transcript in the chloroplast is under the control of nuclear gene products. Using a Chlamydomonas forward genetic screen and whole genome sequencing, we found a mutant defective in PSII activity and mapped the causative gene to be the homolog of Arabidopsis High Fluorescence (HCF244) gene, or CrHCF244. We then demonstrated that CrHCF244 is required for psbA translation in the alga, consistent with the function of HCF244 in Arabidopsis. The Arabidopsis HCF244 gene also partially complemented the algal mutant. These results experimentally support the functional conservation of the homologs in green algae and land plants. Intriguingly, the CrHCF244 mutant also exhibited a relatively high rate of suppressor mutants, pointing to the presence of alternative factor(s)/pathway(s) for D1 translation control. The establishment of CrHCF244 as a psbA translation factor in Chlamydomonas showed the similarities in psbA translation regulation in algae and plants. The future identification of the alternative factor(s) in this alga will provide insights on psbA translation in plants. HighlightWe identified CrHCF244 as a translation factor of psbA in Chlamydomonas. Arabidopsis HCF244 partially complements Chlamydomonas {Delta}CrHCF244 mutant, indicating semi-conservation of the function of this gene between organisms. Suppressor mutants of {Delta}CrHCF244 suggest the presence of alternative translation factors in psbA translation.