Toc64/OEP64 is not essential for the efficient import of proteins into chloroplasts in Arabidopsis thaliana
Toc64/OEP64 is not essential for the efficient import of proteins into chloroplasts in Arabidopsis thaliana
复制标题
DOI：
10.1111/j.1365-313x.2007.03207.x
复制
发表时间：
2007-10-01
期刊：
影响因子：
7.2
通讯作者：
Jarvis, Paul
中科院分区：
文献类型：
--
作者：
Aronsson, Henrik;Boij, Patrik;Jarvis, Paul
Toc64/OEP64在豌豆中被生化鉴定为叶绿体蛋白输入装置的可能成分。在拟南芥中，有三个类似的基因(atTOC64-III、atTOC64-V和atTOC64-I)编码Toc64相关蛋白，已有报道分别定位于叶绿体、线粒体和细胞质。为了评估atToc64-III蛋白在体内叶绿体蛋白输入中的作用，我们鉴定并鉴定了拟南芥基因敲除突变体。Toc64-III单一突变体中没有可检测到的缺陷增加了冗余的可能性，并促使我们也鉴定toc64-V和toc64-I突变体，将它们杂交到toc64-III，并产生双突变和三突变组合。根据各种标准对toc64突变体进行了仔细的分析，包括叶绿素积累、光合作用表现、细胞器超微结构和叶绿体蛋白积累。在每一种情况下，突变植物都无法与野生型区分开来。此外，叶绿体蛋白的导入效率不受toc64突变的影响，即使当检测到atToc64-III蛋白的假定底物(放氧复合体33 kDa亚基的小麦胚翻译前体，OE33)时也是如此。此外，在不同的胁迫条件下(强光、渗透胁迫和低温)，toc64三突变体植株与野生型没有显著差异。这些结果表明，Toc64/OEP64不是有效地将蛋白质导入拟南芥叶绿体所必需的，这一组分的功能意义受到了质疑。
Toc64/OEP64 was identified biochemically in pea as a putative component of the chloroplast protein import apparatus. In Arabidopsis, three paralogous genes (atTOC64-III, atTOC64-V and atTOC64-I) encode Toc64-related proteins, and these have been reported to localize in chloroplasts, mitochondria and the cytosol, respectively. To assess the role of the atToc64-III protein in chloroplast protein import in an in vivo context, we identified and characterized Arabidopsis knockout mutants. The absence of detectable defects in toc64-III single mutants raised the possibility of redundancy, and prompted us to also identify toc64-V and toc64-I mutants, cross them to toc64-III, and generate double- and triple-mutant combinations. The toc64 mutants were analysed carefully with respect to a variety of criteria, including chlorophyll accumulation, photosynthetic performance, organellar ultrastructure and chloroplast protein accumulation. In each case, the mutant plants were indistinguishable from wild type. Furthermore, the efficiency of chloroplast protein import was not affected by the toc64 mutations, even when a putative substrate of the atToc64-III protein (wheatgerm-translated precursor of the 33 kDa subunit of the oxygen-evolving complex, OE33) was examined. Moreover, under various stress conditions (high light, osmotic stress and cold), the toc64 triple-mutant plants were not significantly different from wild type. These results demonstrate that Toc64/OEP64 is not essential for the efficient import of proteins into chloroplasts in Arabidopsis, and draw into question the functional significance of this component.