Analysis of an Arabidopsis mutant with a defect in photosystem II reveals that the integral thylakoid membrane protein PAM71 is involved in manganese and calciu

In vascular plants, the chloroplast NAD(P)H dehydrogenase complex (NDH-C) is assembled from five distinct subcomplexes, the membrane-spanning (subM) and the luminal (subL) subcomplexes, as well as subA, subB, and subE. The assembly process itself is poorly understood. Vascular plant genomes code for two related intrinsic thylakoid proteins, PHOTOSYNTHESIS-AFFECTED MUTANT68 (PAM68), a photosystem II assembly factor, and PHOTOSYNTHESIS-AFFECTED MUTANT68-LIKE (PAM68L). As we show here, inactivation of Arabidopsisthaliana PAM68L in the pam68l-1 mutant identifies PAM68L as an NDH-C assembly factor. The mutant lacks functional NDH holocomplexes and accumulates three distinct NDH-C assembly intermediates (subB, subM, and subA+L), which are also found in mutants defective in subB assembly (ndf5) or subM expression (CHLORORESPIRATORY REDUCTION4-3 mutant). NDH-C assembly in the cyanobacterium Synechocystis sp PCC 6803 and the moss Physcomitrella patens does not require PAM68 proteins, as demonstrated by the analysis of knockout lines for the single-copy PAM68 genes in these species. We conclude that PAM68L mediates the attachment of subB- and subM-containing intermediates to a complex that contains subA and subL. The evolutionary appearance of subL and PAM68L during the transition from mosses like P. patens to flowering plants suggests that the associated increase in the complexity of the NDH-C might have been facilitated by the recruitment of evolutionarily novel assembly factors like PAM68L.

The cyanobacterium Synechocystis sp. PCC 6803 is widely used for research on photosynthesis and circadian rhythms, and also finds application in sustainable biotechnologies. Synechocystis is naturally transformable and undergoes homologous recombination, which enables the development of a variety of tools for genetic and genomic manipulations. To generate multiple gene deletions and/or replacements, marker-less manipulation methods based on counter-selection are generally employed. Currently available methods require two transformation steps with different DNA plasmids.

The chloroplast F₁F_o-ATP synthase/ATPase (cpATPase) couples ATP synthesis to the light-driven electrochemical proton gradient. The cpATPase is a multiprotein complex and consists of a membrane-spanning protein channel (comprising subunit types a, b, b′, and c) and a peripheral domain (subunits α, β, γ, δ, and ε). We report the characterization of the Arabidopsis (Arabidopsis thaliana) CONSERVED ONLY IN THE GREEN LINEAGE160 (AtCGL160) protein (AtCGL160), conserved in green algae and plants. AtCGL160 is an integral thylakoid protein, and its carboxyl-terminal portion is distantly related to prokaryotic ATP SYNTHASE PROTEIN1 (Atp1/UncI) proteins that are thought to function in ATP synthase assembly. Plants without AtCGL160 display an increase in xanthophyll cycle activity and energy-dependent nonphotochemical quenching. These photosynthetic perturbations can be attributed to a severe reduction in cpATPase levels that result in increased acidification of the thylakoid lumen. AtCGL160 is not an integral cpATPase component but is specifically required for the efficient incorporation of the c-subunit into the cpATPase. AtCGL160, as well as a chimeric protein containing the amino-terminal part of AtCGL160 and Synechocystis sp. PCC6803 Atp1, physically interact with the c-subunit. We conclude that AtCGL160 and Atp1 facilitate the assembly of the membranous part of the cpATPase in their hosts, but loss of their functions provokes a unique compensatory response in each organism.