Reinbothe S, Mache R, Reinbothe C
Université Joseph Fourier et Centre National de la Recherche Scientifique, Grenoble, France.
Proc Natl Acad Sci U S A. 2000 Aug 15;97(17):9795-800. 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.
叶绿体必须从细胞质中导入大量蛋白质。通常认为，所有基质蛋白和类囊体蛋白的导入方式相同，且是由质体包膜外层和内层中两种不同的蛋白质导入机制共同作用引起的，这两种机制构成了一般导入位点。在此，我们表明，在大麦、烟草、拟南芥以及其他五种经测试的单子叶和双子叶植物物种的叶绿体中，存在第二个蛋白质转运位点。该导入位点对NADPH：原叶绿素酸酯（Pchlide）氧化还原酶A（pPORA）的胞质前体具有特异性。它将Pchlide的合成与pPORA的导入耦合在一起，从而降低了游离Pchlide的实际水平，由于其光动力学特性，游离Pchlide会对质体造成破坏。因此，植物获得了光保护。
