The balance between protein synthesis and degradation in chloroplasts determines leaf variegation in Arabidopsis yellow variegated mutants
The balance between protein synthesis and degradation in chloroplasts determines leaf variegation in Arabidopsis yellow variegated mutants
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DOI：
10.1105/tpc.106.049270
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发表时间：
2007-04-01
期刊：
影响因子：
11.6
通讯作者：
Sakamoto, Wataru
中科院分区：
文献类型：
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作者：
Miura, Eiko;Kato, Yusuke;Sakamoto, Wataru
拟南芥叶杂色突变体黄色杂色 2 (var2) 是由于叶绿体 FtsH 复合体的主要组成部分 FtsH2 缺失造成的。 FtsH 是类囊体膜中的一种 ATP 依赖性金属蛋白酶，可降解多种叶绿体蛋白。为了了解 FtsH 蛋白水解的作用以及导致叶片杂色的机制，我们鉴定了抑制 var2 叶片杂色的第二位点隐性突变 fu-gaeri1 (fug1)。基于图谱的克隆和随后对 FUG1 基因座的表征表明，它编码与位于叶绿体中的原核翻译起始因子 2 (cpIF2) 同源的蛋白质。我们证明 cpIF2 确实在体内叶绿体蛋白质合成中发挥作用。 fug1 对叶片杂色的抑制不仅在 var2 中观察到，而且在 var1（缺乏 FtsH5）和 var1 var2 中也观察到。因此，FtsH 缺失导致的叶片杂色的抑制很可能归因于叶绿体中蛋白质合成的减少。这一假设得到了观察结果的进一步支持，即叶绿体翻译延伸因子 G 中的另一个可行突变也抑制了 var2 中的叶片杂色。我们认为蛋白质合成与降解之间的平衡是导致拟南芥叶片杂色表型的决定因素之一。
An Arabidopsis thaliana leaf-variegated mutant yellow variegated2 (var2) results from loss of FtsH2, a major component of the chloroplast FtsH complex. FtsH is an ATP-dependent metalloprotease in thylakoid membranes and degrades several chloroplastic proteins. To understand the role of proteolysis by FtsH and mechanisms leading to leaf variegation, we characterized the second-site recessive mutation fu-gaeri1 (fug1) that suppressed leaf variegation of var2. Map-based cloning and subsequent characterization of the FUG1 locus demonstrated that it encodes a protein homologous to prokaryotic translation initiation factor 2 (cpIF2) located in chloroplasts. We show evidence that cpIF2 indeed functions in chloroplast protein synthesis in vivo. Suppression of leaf variegation by fug1 is observed not only in var2 but also in var1 (lacking FtsH5) and var1 var2. Thus, suppression of leaf variegation caused by loss of FtsHs is most likely attributed to reduced protein synthesis in chloroplasts. This hypothesis was further supported by the observation that another viable mutation in chloroplast translation elongation factor G also suppresses leaf variegation in var2. We propose that the balance between protein synthesis and degradation is one of the determining factors leading to the variegated phenotype in Arabidopsis leaves.