An Arabidopsis chloroplast-targeted Hsp101 homologue, APG6, has an essential role in chloroplast development as well as heat-stress response
An Arabidopsis chloroplast-targeted Hsp101 homologue, APG6, has an essential role in chloroplast development as well as heat-stress response
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DOI：
10.1111/j.1365-313x.2006.02873.x
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发表时间：
2006-10-01
期刊：
影响因子：
7.2
通讯作者：
Shinozaki, Kazuo
中科院分区：
文献类型：
--
作者：
Myouga, Fumiyoshi;Motohashi, Reiko;Shinozaki, Kazuo
分析白化病或淡绿（apg）突变体对于鉴定负责叶绿体发育和色素合成的核基因是重要的。通过对11 000个拟南芥Ds标记株系的筛选，我们鉴定出38个apg突变体。一种突变体apg 6在编码APG 6（ClpB 3）的基因中含有Ds插入，APG 6是热休克蛋白Hsp 101（ClpB 1）的同源物。我们分离体细胞回复突变体，并确定了两个DS标记和一个T-DNA标记的突变等位基因apg 6。所有三个等位基因给出了相同的淡绿色表型。这些结果表明，APG 6是重要的叶绿体发育。APG 6蛋白含有转运肽，定位于叶绿体中。apg 6淡绿色细胞的质体比野生型小，含有不发达的类囊体膜。APG 6 mRNA在热激胁迫下大量积累，而在非生物胁迫下不积累。在正常条件下，APG 6在成熟植物的根尖、器官边界区域、质体以原质体形式存在的生殖组织中组成型表达，在茎和叶中少量表达。此外，在转基因植物中组成型过表达APG 6抑制叶绿体发育，并导致温和的淡绿色表型。apg 6突变体中与光合作用相关的叶绿体蛋白质含量显著降低。这些结果表明，APG 6功能作为分子伴侣参与质体分化介导的内部类囊体膜的形成和赋予热胁迫期间的叶绿体耐热性。APG 6蛋白不仅参与叶绿体的热应激反应，而且对叶绿体发育也是必不可少的。
Analysis of albino or pale-green (apg) mutants is important for identifying nuclear genes responsible for chloroplast development and pigment synthesis. We have identified 38 apg mutants by screening 11 000 Arabidopsis Ds-tagged lines. One mutant, apg6, contains a Ds insertion in a gene encoding APG6 (ClpB3), a homologue of the heat-shock protein Hsp101 (ClpB1). We isolated somatic revertants and identified two Ds-tagged and one T-DNA-tagged mutant alleles of apg6. All three alleles gave the same pale-green phenotype. These results suggest that APG6 is important for chloroplast development. The APG6 protein contains a transit peptide and is localized in chloroplasts. The plastids of apg6 pale-green cells were smaller than those of the wild type, and contained undeveloped thylakoid membranes. APG6 mRNA accumulated in response to heat shock in various organs, but not in response to other abiotic stresses. Under normal conditions, APG6 is constitutively expressed in the root tips, the organ boundary region, the reproductive tissues of mature plants where plastids exist as proplastids, and slightly in the stems and leaves. In addition, constitutive overexpression of APG6 in transgenic plants inhibited chloroplast development and resulted in a mild pale-green phenotype. The amounts of chloroplast proteins related to photosynthesis were markedly decreased in apg6 mutants. These results suggest that APG6 functions as a molecular chaperone involved in plastid differentiation mediating internal thylakoid membrane formation and conferring thermotolerance to chloroplasts during heat stress. The APG6 protein is not only involved in heat-stress response in chloroplasts, but is also essential for chloroplast development.