A substrate-independent, 14:3:3 protein-mediated plastid import pathway of NADPH:protochlorophyllide oxidoreductase A.
Plastids are semiautonomous organelles that contain only limited coding information in their own DNA. Because most of their genome was transferred to the nucleus after their endosymbiotic origin, plastids must import the major part of their protein constituents from the cytosol. The exact role of cytosolic targeting factors in the regulation of plastid protein import has not been determined. Here, we report that the nucleus-encoded NADPH:protochlorophyllide (Pchlide) oxidoreductase A plastid precursor (pPORA) can use two different plastid import pathways that differ by the requirements for cytosolic 14:3:3 proteins and Hsp70. pPORA synthesized in a wheat germ lysate segregated into different precursor fractions. While import of free pPORA and only Hsp70-complexed pPORA was Pchlide-dependent and involved the previously identified Pchlide-dependent translocon, 14:3:3 protein- and Hsp70-complexed pPORA was transported into Pchlide-free chloroplasts through the Toc75-containing standard translocon at the outer chloroplast membrane/translocon at the inner chloroplast membrane machinery. A 14:3:3 protein binding site was identified in the mature region of the (35)S-pPORA, which governed 14:3:3 protein- and Hsp70-mediated, Pchlide-independent plastid import. Collectively, our results reveal that the import of pPORA into the plastids is tightly regulated and involves different cytosolic targeting factors and plastid envelope translocon complexes.
Schemenewitz
Andreas
A
Lehrstuhl für Pflanzenphysiologie, Ruhr-Universität Bochum, Universitätsstrasse 150, Gebäude ND, D-44801 Bochum, Germany.
Pollmann
Stephan
S
Reinbothe
Christiane
C
Reinbothe
Steffen
S
D048948:14-3-3 Proteins / Q000378:metabolism*; D000818:Animals; D001665:Binding Sites; D003432:Cross-Linking Reagents / Q000494:pharmacology; D018840:HSP70 Heat-Shock Proteins / Q000378:metabolism; D001467:Hordeum; D008027:Light; D009154:Mutation / Q000235:genetics; D044925:Oxidoreductases Acting on CH-CH Group Donors / Q000096:biosynthesis / Q000378:metabolism*; D010105:Oxygenases / Q000378:metabolism; D018087:Plastids / Q000187:drug effects / Q000378:metabolism* / Q000528:radiation effects; D011485:Protein Binding / Q000187:drug effects / Q000528:radiation effects; D014176:Protein Biosynthesis / Q000187:drug effects / Q000528:radiation effects; D011487:Protein Conformation / Q000187:drug effects / Q000528:radiation effects; D011498:Protein Precursors / Q000737:chemistry / Q000378:metabolism; D021381:Protein Transport / Q000187:drug effects / Q000528:radiation effects; D011521:Protochlorophyllide / Q000494:pharmacology; D011817:Rabbits; D013379:Substrate Specificity / Q000187:drug effects / Q000528:radiation effects
D048948:14-3-3 Proteins; D003432:Cross-Linking Reagents; D018840:HSP70 Heat-Shock Proteins; D011498:Protein Precursors; D011521:Protochlorophyllide; D010105:Oxygenases; C115272:chlorophyll a oxygenase; D044925:Oxidoreductases Acting on CH-CH Group Donors; C023886:protochlorophyllide reductase