Department of Molecular Genetics and Cell Biology, University of Chicago, Chicago, IL 60637, USA.
Proc Natl Acad Sci U S A. 2010 Jul 20;107(29):13177-82. doi: 10.1073/pnas.0910943107. Epub 2010 Jul 6.
Plant heat shock protein Hsp70 is the major target of HopI1, a virulence effector of pathogenic Pseudomonas syringae. Hsp70 is essential for the virulence function of HopI1. HopI1 directly binds Hsp70 through its C-terminal J domain and stimulates Hsp70 ATP hydrolysis activity in vitro. In plants, HopI1 forms large complexes in association with Hsp70 and induces and recruits cytosolic Hsp70 to chloroplasts, the site of HopI1 localization. Deletion of a central P/Q-rich repeat region disrupts HopI1 virulence but not Hsp70 interactions or association with chloroplasts. Thus, HopI1 must not only bind Hsp70 through its J domain, but likely actively affects Hsp70 activity and/or specificity. At high temperature, HopI1 is dispensable for P. syringae pathogenicity, unless excess Hsp70 is provided. A working hypothesis is that Hsp70 has a defense-promoting activity(s) that HopI1 or high temperature can subvert. Enhanced susceptibility of Hsp70-depleted plants to nonpathogenic strains of P. syringae supports a defense-promoting role for Hsp70.
植物热休克蛋白 Hsp70 是病原菌丁香假单胞菌的毒力效应子 HopI1 的主要靶标。Hsp70 对 HopI1 的毒力功能是必不可少的。HopI1 通过其 C 端 J 结构域直接与 Hsp70 结合，并在体外刺激 Hsp70 的 ATP 水解活性。在植物中，HopI1 与 Hsp70 形成大复合物，并诱导和招募细胞质 Hsp70 到叶绿体，即 HopI1 定位的部位。缺失中央 P/Q 富含重复区会破坏 HopI1 的毒力，但不影响 Hsp70 相互作用或与叶绿体的结合。因此，HopI1 不仅必须通过其 J 结构域结合 Hsp70，而且可能还积极影响 Hsp70 的活性和/或特异性。在高温下，HopI1 对丁香假单胞菌的致病性不是必需的，除非提供过量的 Hsp70。一个可行的假设是，Hsp70 具有防御促进活性（s），HopI1 或高温可以颠覆这些活性。Hsp70 耗竭的植物对非致病性丁香假单胞菌菌株的敏感性增强，支持 Hsp70 具有防御促进作用。
