Studies ofCrHCF244reveal similarities and differences inpsbAtranslation betweenChlamydomonas reinhardtiiandArabidopsis thaliana

Abstract

AbstractTranslation ofpsbA, the chloroplast gene that encodes the D1 subunit of Photosystem II (PSII), is important for both PSII biogenesis and repair. The translation of thepsbAtranscript in the chloroplast is under the control of nuclear gene products. Using aChlamydomonasforward genetic screen and whole genome sequencing, we found a mutant defective in PSII activity and mapped the causative gene to be the homolog ofArabidopsis High Fluorescence(HCF244) gene, orCrHCF244. We then demonstrated that CrHCF244 is required forpsbAtranslation in the alga, consistent with the function of HCF244 inArabidopsis. TheArabidopsis HCF244gene also complemented the algal mutant. These results experimentally support the functional conservation of the homologs in green algae and land plants. However, these studies also revealed differences inpsbAtranslation inChlamydomonasandArabidopsis. Loss of HCF244 inArabidopsisresults in a large decrease in chlorophyll. In contrast, there is no significant loss of chlorophyll inChlamydomonaswhenCrHCF244is knocked out. This observation supports the uncoupling of D1 translation and chlorophyll association in algae as reported recently in anohp2mutant, which is defective in chlorophyll delivery. Intriguingly, theCrHCF244mutant also exhibited a relatively high rate of suppressor mutants, pointing to the presence of alternative pathway(s) for D1 translation control. The characterization of both the conserved aspects and the differences inpsbAtranslation control between algae and plants will help elucidate how this process is regulated.HighlightWe identified CrHCF244 as a translation factor ofpsbAinChlamydomonas.Characterization of this protein and genetic examinations of other previously identifiedpsbAtranslation factors inChlamydomonasreveal similarities and differences inpsbAtranslation betweenChlamydomonasandArabidopsis.