The Arabidopsis TELLURITE RESISTANCE C is required for the functionality of both photosystems by supplying manganese and calcium.

The oxygen-evolving complex (OEC) of photosystem II (PSII) contains a Mn4CaO5 cluster that catalyzes the light-driven oxidation of water. In Arabidopsis thaliana, optimal PSII function requires the thylakoid membrane-localized manganese transporter PHOTOSYNTHESIS AFFECTED MUTANT 71 (PAM71). Here, we show that overexpression of TELLURITE RESISTANCE C (TerC) restores low chloroplast manganese levels, O2 evolution rates, and growth defects in PAM71 knock-out plants. A TerC knock-down allele (amiR-TerC) exhibits OEC-related phenotypic changes similar to those observed in pam71, including altered period-four S-state oscillations of the OEC and PSII charge-recombination energetics. Unlike pam71, amiR-TerC accumulates a photosystem I (PSI) subcomplex lacking the subunits PsaL, PsaH and PsaO, impairing the ability to perform state transition. Diminished PSII activity and alterations in PSI are more pronounced under low calcium conditions, and light-dependent Ca2+ accumulation in isolated thylakoids is reduced in amiR-TerC. When expressed heterologously, TerC suppresses the Mn2+- and Ca2+-sensitive phenotypes of yeast mutant strains Δpmr1 and Δpmr1Δgdt1, respectively. We suggest that TerC is involved in the transport of Mn2+ and Ca2+ across the thylakoid membrane, and that the absence of this function contributes to the albinotic phenotype observed in the terc seedlings.