An outer envelope membrane component of the plastid protein import apparatus plays an essential role in Arabidopsis
An outer envelope membrane component of the plastid protein import apparatus plays an essential role in Arabidopsis
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DOI：
10.1111/j.1365-313x.2004.02024.x
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发表时间：
2004-04-01
期刊：
影响因子：
7.2
通讯作者：
Jarvis, P
中科院分区：
文献类型：
--
作者：
Constan, D;Patel, R;Jarvis, P
位于叶绿体外被膜的易位子，34 kDa（Toc 34）是质体外被膜内蛋白质输入装置的GTP结合组分。拟南芥基因组编码Toc 34的两个同源物，命名为atToc 33和atToc 34。在这份报告中，我们描述了两个atToc 34敲除突变体，质体蛋白导入3-1（ppi 3 -1）和ppi 3 -2的鉴定和表征。在整个发育过程中，PPI 3突变体的气生组织与野生型相似，并且含有结构正常的叶绿体，这些叶绿体能够在体外有效地导入Rubisco小亚基前体（PrSS）。在绿色组织中不存在明显的ppi 3表型，推测反映了atToc 33在突变体中替代atToc 34的能力，以及atTOC 33基因在这些组织中相对高水平的表达。在atTOC 33以低得多的水平表达的根中，在两种突变体中观察到显著的生长缺陷：ppi 3根比野生型根短约20-30%。试图鉴定缺乏atToc 34和atToc 33的双纯合子（通过将ppi 3突变体与atToc 33敲除突变体ppi 1杂交）是不成功的，这表明atToc 33/atToc 34提供的功能在早期发育过程中是必不可少的。ppi 1纯合和ppi 3杂合的植株表现出比ppi 1单突变体严重得多的褪绿表型。此外，这些植物的角果含有约25%的败育种子，表明双纯合突变是胚胎致死的。这些数据表明，atToc 33/atToc 34在质体蛋白输入过程中发挥着重要作用，并表明atToc 34亚型对根中质体生物发生相对更重要。
Translocon at the outer envelope membrane of chloroplasts, 34 kDa (Toc34) is a GTP-binding component of the protein import apparatus within the outer envelope membrane of plastids. The Arabidopsis genome encodes two homologues of Toc34, designated atToc33 and atToc34. In this report, we describe the identification and characterization of two atToc34 knockout mutants, plastid protein import 3-1 (ppi3-1) and ppi3-2. Aerial tissues of the ppi3 mutants appeared similar to the wild type throughout development, and contained structurally normal chloroplasts that were able to efficiently import the Rubisco small subunit precursor (prSS) in vitro. The absence of an obvious ppi3 phenotype in green tissues presumably reflects the ability of atToc33 to substitute for atToc34 in the mutant, and the relatively high level of expression of the atTOC33 gene in these tissues. In the roots, where atTOC33 is expressed at a much lower level, significant growth defects were observed in both mutants: ppi3 roots were approximately 20-30% shorter than wild-type roots. Attempts to identify a double homozygote lacking atToc34 and atToc33 (by crossing the ppi3 mutants with ppi1, an atToc33 knockout mutant) were unsuccessful, indicating that the function provided by atToc33/atToc34 is essential during early development. Plants that were homozygous for ppi1 and heterozygous for ppi3 displayed a chlorotic phenotype much more severe than that of the ppi1 single mutant. Furthermore, the siliques of these plants contained approximately 25% aborted seeds, indicating that the double homozygous mutation is embryo lethal. The data demonstrate that atToc33/atToc34 performs a central and essential role during plastid protein import, and indicate that the atToc34 isoform is relatively more important for plastid biogenesis in roots.