AtCGL160 recruits chloroplast coupling factor 1

ATP synthases couple the generation of chemical energy to a transmembrane electro-chemical potential. Like ATP synthases in bacteria and mitochondria, chloroplast ATP synthases consist of a membrane-spanning (CF O ) and a soluble coupling factor (CF 1 ). Accessory factors facilitate subunit production and orchestrate the assembly of the functional CF 1 -CF O complex. It was previously shown that the accessory factor CGL160 promotes the formation of plant CF O and performs a similar function in the assembly of its c-ring to that of the distantly related bacterial Atp1/UncI protein. In this study, we show that the N-terminal portion of CGL160 (AtCGL160N), which is specific to the green lineage, is required for late steps in CF 1 -CF O assembly in Arabidopsis thaliana . In plants that lacked this stroma-exposed domain, photosynthesis was impaired, and amounts of CF 1 -CF O were reduced to about 65% of the wild-type level. Loss of AtCGL160N did not perturb c-ring formation, but led to a 10-fold increase in the numbers of CF 1 sub-complexes in the stroma relative to the wild type and the CF 1 assembly mutant atcgld11-1 . Co-immunoprecipitation and protein crosslinking assays revealed an association of AtCGL160 with CF 1 subunits. Yeast two-hybrid assays localized the interaction to a stretch of AtCGL160N that binds to the thylakoid-proximal domain of CF 1 -β that includes the conserved DELSEED motif. We therefore propose that AtCGL160 has acquired an additional function in the recruitment of soluble CF 1 to a membrane-integral CF O sub-complex, which is critical for the modulation of CF 1 -CF O activity and photosynthesis in chloroplasts.