Impact of the Simultaneous Loss of the Plastid Envelope-Localized Homologous Pair Ycf10 and DLDG1 in Plant Growth and Photosynthetic Performance.
Ycf10 and DLDG1 are homologous proteins embedded in the chloroplast envelope membranes (EM) and encoded in the plastidial and nuclear genomes, respectively. We previously characterized Arabidopsis dldg1 and tobacco ycf10 mutants, and showed that these proteins mediate proton transport across the EM, thereby influencing ATP synthesis and the non-photochemical quenching (NPQ) induction. However, the consequences of the simultaneous loss of Ycf10/DLDG1 homologs have remained unclear. Here, we generated and analyzed Arabidopsis ycf10 and ycf10-dldg1 double mutants. These mutants exhibited a pale-green phenotype under continuous light conditions, which was complemented by the exogenous addition of NaCl, as previously observed in mutants lacking the plastid EM-localized K+/H+ antiporters KEA1 and KEA2. Both single mutants (ycf10 and dldg1), as well as the ycf10-dldg1 double mutant, showed enhanced NPQ induction compared with wild-type. Furthermore, the ycf10-dldg1 double mutant showed stronger NPQ induction than either single mutant upon transition from dark to light, suggesting that Ycf10 and DLDG1 function independently while playing redundant roles. These mutants also showed reduced stomatal conductance and sugar accumulation compared with the wild-type. Together, these findings indicate that EM-localized DLDG1 and Ycf10 act in concert to maintain chloroplast proton/ion homeostasis, contributing to chloroplast pH homeostasis for sustaining plant growth and efficient photosynthesis.