ABC1K1/PGR6 kinase: a regulatory link between photosynthetic activity and chloroplast metabolism
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Abstract
Summary Arabidopsis proton gradient regulation ( pgr ) mutants have high chlorophyll fluorescence and reduced non‐photochemical quenching ( NPQ ) caused by defects in photosynthetic electron transport. Here, we identify PGR 6 as the chloroplast lipid droplet (plastoglobule, PG ) kinase ABC 1 K 1 (activity of bc1 complex kinase 1). The members of the ABC 1/ ADCK / U bi B family of atypical kinases regulate ubiquinone synthesis in bacteria and mitochondria, and impact various metabolic pathways in plant chloroplasts. Here, we demonstrate that abc1k1 has a unique photosynthetic and metabolic phenotype that is distinct from that of the abc1k3 homolog. The abc1k1/pgr6 single mutant is specifically deficient in the electron carrier plastoquinone, as well as in β–carotene and the xanthophyll lutein, and is defective in membrane antioxidant tocopherol metabolism. After 2 days of continuous high light stress, abc1k1/pgr6 plants suffer extensive photosynthetic and metabolic perturbations, strongly affecting carbohydrate metabolism. Remarkably, however, the mutant acclimates to high light after 7 days together with a recovery of carotenoid levels and a drastic alteration in the starch‐to‐sucrose ratio. Moreover, ABC 1 K 1 behaves as an active kinase and phosphorylates VTE 1, a key enzyme of tocopherol (vitamin E ) metabolism in vitro . Our results indicate that the ABC 1 K 1 kinase constitutes a new type of regulatory link between photosynthetic activity and chloroplast metabolism.
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