Heat Shock Protein Cognate 70-4 and an E3 Ubiquitin Ligase, CHIP, Mediate Plastid-Destined Precursor Degradation through the Ubiquitin-26S Proteasome System in Arabidopsis
Heat Shock Protein Cognate 70-4 and an E3 Ubiquitin Ligase, CHIP, Mediate Plastid-Destined Precursor Degradation through the Ubiquitin-26S Proteasome System in Arabidopsis
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DOI：
10.1105/tpc.109.071548
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发表时间：
2009-12-01
期刊：
影响因子：
11.6
通讯作者：
Hwang, Inhwan
中科院分区：
文献类型：
--
作者：
Lee, Sookjin;Lee, Dong Wook;Hwang, Inhwan
以叶绿体为靶标的蛋白质以未折叠的前体的形式通过细胞质。如果蛋白质在细胞质中积累，它们可以形成非特异性聚集体，导致严重的细胞损伤。在这里，我们证明了在拟南芥细胞中，高水平的质体前体是通过泛素-蛋白酶体系统(UPS)降解的。胞质热休克蛋白同源70-4(Hsc70-4)和Hsc70相互作用蛋白的E3连接酶羧基末端(CHIP)在叶绿体蛋白导入2植株中被高度诱导，在Toc159处有T-DNA插入，表现为白化表型和蛋白质进入叶绿体的严重缺陷。当进口缺陷的叶绿体靶向报告蛋白在原生质体中瞬时表达时，Hsc70-4和CHIP共同介导了叶绿体前体的降解。Hsc70-4识别转运肽中的特定序列基序，从而导致前体通过UPS降解。CHIP与Hsc70-4相互作用，在Hsc70-4介导的蛋白质降解中起E3连接酶的作用。通过对Hsc70-1突变背景下的Hsc70-4 RNA干扰植株的分析，证实了Hsc70-4的生理作用。Hsc70水平较低的植株表现出胚胎发育异常，导致缺陷幼苗表现出高水平的活性氧和单素化的Lhcb4前体。我们认为，Hsc70-4和CHIP介导了以叶绿体为目标的前体降解，以防止胞质前体积累，从而在胚胎发育中发挥关键作用。
Plastid-targeted proteins pass through the cytosol as unfolded precursors. If proteins accumulate in the cytosol, they can form nonspecific aggregates that cause severe cellular damage. Here, we demonstrate that high levels of plastid precursors are degraded through the ubiquitin-proteasome system (UPS) in Arabidopsis thaliana cells. The cytosolic heat shock protein cognate 70-4 (Hsc70-4) and E3 ligase carboxy terminus of Hsc70-interacting protein (CHIP) were highly induced in plastid protein import 2 plants, which had a T-DNA insertion at Toc159 and showed an albino phenotype and a severe defect in protein import into chloroplasts. Hsc70-4 and CHIP together mediated plastid precursor degradation when import-defective chloroplast-targeted reporter proteins were transiently expressed in protoplasts. Hsc70-4 recognized specific sequence motifs in transit peptides and thereby led to precursor degradation through the UPS. CHIP, which interacted with Hsc70-4, functioned as an E3 ligase in the Hsc70-4-mediated protein degradation. The physiological role of Hsc70-4 was confirmed by analyzing Hsc70-4 RNA interfernce plants in an hsc70-1 mutant background. Plants with lower Hsc70 levels exhibited abnormal embryogenesis, resulting in defective seedlings that displayed high levels of reactive oxygen species and monoubiquitinated Lhcb4 precursors. We propose that Hsc70-4 and CHIP mediate plastid-destined precursor degradation to prevent cytosolic precursor accumulation and thereby play a critical role in embryogenesis.