A Second, Substrate-Dependent Site of Protein Import into Chloroplasts

• Published in: Proceedings of the National Academy of Sciences - PNAS 2000-08, Vol.97 (17), p.9795-9800
• Main Authors: Reinbothe, Steffen, Mache, Regis, Reinbothe, Christiane
• Format: Article
• Language: English
• Subjects: Antibodies - pharmacology; Barley; Binding, Competitive; Biological Sciences; Biological Transport - drug effects; Biology; Chlorophyll; Chloroplasts; Chloroplasts - drug effects; Chloroplasts - enzymology; Chloroplasts - metabolism; Enzyme Precursors - metabolism; Flowers & plants; Hordeum - cytology; Hordeum - drug effects; Hordeum - enzymology; Hordeum - metabolism; Imports; Molecules; Oxidoreductases - metabolism; Oxidoreductases Acting on CH-CH Group Donors; Plant Cells; Plant Proteins - metabolism; Plants; Plants - drug effects; Plants - enzymology; Plants - metabolism; Plastids; Pretreatment; Protein precursors; Protein Precursors - metabolism; Proteins; Protochlorophyllide - metabolism; Receptors; Substrate Specificity; Tetrahydrofolate Dehydrogenase - metabolism
• ISSN: 0027-8424; 1091-6490
• DOI: 10.1073/pnas.160242597

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.