DAY LENGTH DEPENDENT DELAYED GREENING1, the Arabidopsis Homolog of the Cyanobacterial H+ Extrusion Protein, is Essential for Chloroplast pH Regulation and Optimization of Non Photochemical Quenching.
Plants convert solar energy into chemical energy through photosynthesis, which supports almost all life activities on earth. Because the intensity and quality of sunlight can change dramatically throughout the day, various regulatory mechanisms help plants adjust their photosynthetic output accordingly, including the regulation of light energy accumulation to prevent the generation of damaging reactive oxygen species. Non photochemical quenching (NPQ) is a regulatory mechanism that dissipates excess light energy, but how it is regulated is not fully elucidated. Herein, we report a new NPQ regulatory protein named Day Length dependent Delayed Greening1 (DLDG1) The Arabidopsis DLDG1 associates with the chloroplast envelope membrane, and the dldg1 mutant had a large NPQ value compared with wild type. The mutant also had a pale green phenotype in developing leaves but only under continuous light; this phenotype was not observed when dldg1 was cultured in the dark for =8 h per day. DLDG1 is a homolog of the plasma membrane localizing cyanobacterial proton extrusion protein A that is required for light induced H+ extrusion, and also shows similarity in its amino acid sequence to that of Ycf10 encoded in the plastid genome. Arabidopsis DLDG1 enhances the growth retardation phenotype of the Escherichia coli K+/H+ antiporter mutant, and the everted membrane vesicles of the E. coli expressing DLDG1 show the K+/H+ antiport activity. Our findings suggest that DLDG1 functionally interacts with Ycf10 to control H+ homeostasis in chloroplasts, which is important for the light acclimation response, by optimizing the extent of NPQ.
Plant cell physiology