Nucleus-Encoded Light-Harvesting Chlorophyll a/b Proteins are Imported Normally into Chlorophyll b-Free Chloroplasts of Arabidopsis

作     者：Sabine Nick Jorg Meurer Jurgen Soil Elisabeth Ankele 

作者机构：Dept Biologie I-Botanik Biozentrum LMU Munchen Grosshadernerstrasse 2-4 D-82152 Planegg-Martinsried Germany Munich Center for Integrated Protein Science ClPSM Ludwig-Maximilians-Universitat Munchen Feodor-Lynen-Strasse 25 D-81377 Munich Germany 

出 版 物：《Molecular Plant》 (分子植物（英文版）)

年 卷 期：2013年第6卷第3期

页      面：860-871页

核心收录：

学科分类：0710[理学-生物学] 071010[理学-生物化学与分子生物学] 081704[工学-应用化学] 07[理学] 08[工学] 0817[工学-化学工程与技术] 09[农学] 0903[农学-农业资源与环境] 0901[农学-作物学] 090302[农学-植物营养学] 0902[农学-园艺学] 

基　　金：supported by grants from the Deutsche Forschungsgemeinschaft 

主　　题：chloroplast import LHCPs cao-1 protein complex assembly thylakoid membranes photosynthesis. 

摘      要：Chloroplast-located proteins which are encoded by the nuclear genome have to be imported from the cytosol into the organelle in a posttranslational manner. Among these nuclear-encoded chloroplast proteins are the light- harvesting chlorophyll a/b-binding proteins （LHCPs）. After translation in the cytosol, precursor proteins of LHCPs are imported via the TOC/TIC translocase, processed to their mature size to insert into thylakoid membranes where they recruit chlorophylls a and b to form pigment-protein complexes. The translocation of proteins is a highly regulated process which employs several regulators. To analyze whether CAO （chlorophyll a oxigenase） which converts chlorophyll a to chlorophyll b at the inner chloroplast membrane, is one of these regulators, we performed import reactions utilizing a homozygous loss-of-function mutant （cao-1）. We imported in vitro translated and 35S-labeled precursor proteins of light- harvesting proteins of photosystem II LHCB1, LHCB4, and LHCB5 into chloroplasts isolated from cao-1 and show that import of precursor proteins and their processing to mature forms are not impaired in the mutant. Therefore, regulation of the import machinery cannot be responsible for the decreased steady-state levels of light-harvesting complex （LHC） proteins. Regulation does not take place at the transcriptional level either, because Lhcb mRNAs are not down-regulated. Additionally, reduced steady-state levels of LHCPs also do not occur due to posttranslational turnover of non-functional LHCPs in chloroplasts. Taken together, our data show that plants in the absence of CAO and therefore devoid of chlorophyll b are not influenced in their import behavior of LHC proteins.