Zwiesler-Vollick Julie, Plovanich-Jones Anne E, Nomura Kinya, Bandyopadhyay Sruti, Joardar Vinita, Kunkel Barbara N, He Sheng Yang
Department of Energy Plant Research Laboratory, 206 Plant Biology Building, Michigan State University, East Lansing, MI 48824, USA.
Mol Microbiol. 2002 Sep;45(5):1207-18. doi: 10.1046/j.1365-2958.2002.02964.x.
Pseudomonas syringae pv. tomato (Pst) strain DC3000 infects the model plants Arabidopsis thaliana and tomato, causing disease symptoms characterized by necrotic lesions surrounded by chlorosis. One mechanism used by Pst DC3000 to infect host plants is the type III protein secretion system, which is thought to deliver multiple effector proteins to the plant cell. The exact number of type III effectors in Pst DC3000 or any other plant pathogenic bacterium is not known. All known type III effector genes of P. syringae are regulated by HrpS, an NtrC family protein, and the HrpL alternative sigma factor, which presumably binds to a conserved cis element (called the "hrp box") in the promoters of type III secretion-associated genes. In this study, we designed a search motif based on the promoter sequences conserved in 12 published hrp operons and putative effector genes in Pst DC3000. Seventy-three predicted genes were retrieved from the January 2001 release of the Pst DC3000 genome sequence, which had 95% genome coverage. The expression of the 73 genes was analysed by microarray and Northern blotting, revealing 24 genes/operons (including eight novel genes), the expression of which was consistently higher in hrp-inducing minimal medium than in nutrient-rich Luria-Bertani broth. Expression of all eight genes was dependent on the hrpS gene. Most were also dependent on the hrpL gene, but at least one was dependent on the hrpS gene, but not on the hrpL gene. An AvrRpt2-based type III translocation assay provides evidence that some of the hrpS-regulated novel genes encode putative effector proteins.
丁香假单胞菌番茄致病变种（Pst）DC3000菌株可感染模式植物拟南芥和番茄，引发以坏死斑周围黄化为特征的病害症状。Pst DC3000用于感染宿主植物的一种机制是Ⅲ型蛋白分泌系统，该系统被认为可将多种效应蛋白传递至植物细胞。Pst DC3000或任何其他植物致病细菌中Ⅲ型效应蛋白的确切数量尚不清楚。丁香假单胞菌所有已知的Ⅲ型效应蛋白基因均受HrpS（一种NtrC家族蛋白）和HrpL替代σ因子调控，后者可能与Ⅲ型分泌相关基因启动子中的保守顺式元件（称为“hrp框”）结合。在本研究中，我们基于12个已发表的hrp操纵子和Pst DC3000中假定效应蛋白基因的启动子序列保守性设计了一个搜索基序。从2001年1月发布的Pst DC3000基因组序列中检索到73个预测基因，该序列的基因组覆盖率为95%。通过微阵列和Northern印迹分析这73个基因的表达，发现24个基因/操纵子（包括8个新基因），其在hrp诱导的基本培养基中的表达始终高于营养丰富的Luria-Bertani肉汤。所有8个基因的表达均依赖于hrpS基因。大多数基因也依赖于hrpL基因，但至少有一个基因依赖于hrpS基因，而不依赖于hrpL基因。基于AvrRpt2的Ⅲ型转运分析提供了证据，表明一些受hrpS调控的新基因编码假定的效应蛋白。
