A second, substrate-dependent site of protein import into chloroplasts.
Chloroplasts must import a large number of proteins from the cytosol. It generally is assumed that this import proceeds for all stromal and thylakoid proteins in an identical manner and is caused by the operation of two distinctive protein import machineries in the outer and inner plastid envelope, which form the general import site. Here we show that there is a second site of protein translocation into chloroplasts of barley, tobacco, Arabidopsis thaliana, and five other tested monocotyledonous and dicotyledonous plant species. This import site is specific for the cytosolic precursor of the NADPH:protochlorophyllide (Pchlide) oxidoreductase A, pPORA. It couples Pchlide synthesis to pPORA import and thereby reduces the actual level of free Pchlide, which, because of its photodynamic properties, would be destructive to the plastids. Consequently, photoprotection is conferred onto the plant.
Université Joseph Fourier et Centre National de la Recherche Scientifique, Grenoble, France.
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D000906:Antibodies / Q000494:pharmacology; D001667:Binding, Competitive; D001692:Biological Transport / Q000187:drug effects; D002736:Chloroplasts / Q000187:drug effects / Q000201:enzymology / Q000378:metabolism*; D004792:Enzyme Precursors / Q000378:metabolism; D001467:Hordeum / Q000166:cytology / Q000187:drug effects / Q000201:enzymology / Q000378:metabolism; D010088:Oxidoreductases / Q000378:metabolism; D044925:Oxidoreductases Acting on CH-CH Group Donors; D059828:Plant Cells; D010940:Plant Proteins / Q000378:metabolism*; D010944:Plants / Q000187:drug effects / Q000201:enzymology / Q000378:metabolism*; D011498:Protein Precursors / Q000378:metabolism; D011521:Protochlorophyllide / Q000378:metabolism; D013379:Substrate Specificity; D013762:Tetrahydrofolate Dehydrogenase / Q000378:metabolism
D000906:Antibodies; D004792:Enzyme Precursors; D010940:Plant Proteins; D011498:Protein Precursors; D011521:Protochlorophyllide; D010088:Oxidoreductases; D044925:Oxidoreductases Acting on CH-CH Group Donors; C023886:protochlorophyllide reductase; D013762:Tetrahydrofolate Dehydrogenase