Analysis of Erwinia chrysanthemi EC16 pelE::uidA, peIL::uidA, and hrpN::uidA mutants reveals strain-specific atypical regulation of the Hrp type III secretion system
Analysis of Erwinia chrysanthemi EC16 pelE::uidA, peIL::uidA, and hrpN::uidA mutants reveals strain-specific atypical regulation of the Hrp type III secretion system
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DOI：
10.1094/mpmi.2004.17.2.184
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发表时间：
2004-02-01
影响因子：
3.5
通讯作者：
Collmer, A
中科院分区：
文献类型：
--
作者：
Ham, JH;Cui, Y;Collmer, A
植物病原体欧文氏菌产生多种因子，这些因子与其在各种宿主中引起软腐病的能力有关。这些包括HrpN，由Hrp III型分泌系统分泌的harpin; PelE，由H型系统分泌的几种主要果胶酸裂解酶同工酶之一;和PeIL，由II型系统分泌的几种次级Pel之一。我们在E. chalcii EC 16的培养基组成和生长阶段对基因表达的影响（如用uidA融合和北方分析所确定的）和对毒力的影响。pelE能被多聚半乳糖醛酸诱导，而pelL不能，hrpN在营养丰富的King's培养基B和中性盐培养基中均能表达。chalcoheniCUCPB 1237和3937与许多其他植物病原细菌一样，在复合培养基中被抑制，在酸性pH基本培养基中被诱导。对野生型和hrpL：：OmegaCm（r）和hrpS：：OmegaCm（r）突变体的hrpN和hrpL表达的北方印迹分析显示，hrpN表达依赖于HrpL替代σ因子，而后者的表达又依赖于HrpS推定的σ（54）增强子结合蛋白。pelE和hrpN的表达在对数生长期后期强烈增加。为了测试群体感应在这种表达模式中的可能作用，在大肠埃希氏菌中克隆了expI/expR基因座，基于其直接产生酰基高丝氨酸内酯的能力，然后用于构建pelE：：uidA、pelL：：uidA和hrpN：：uidA欧文氏菌菌株中的expI突变。expI基因突变对hrpN和pelE的生长期依赖性表达及E.在wit-loof菊苣叶chicori。hrpN在E. Chelovi导致菊苣叶上的病斑尺寸减小约50%，而对感染起始没有影响。
The plant pathogen Erwinia chrysanthemi produces a variety of factors that have been implicated in its ability to cause soft-rot diseases in various hosts. These include HrpN, a harpin secreted by the Hrp type III secretion system; PelE, one of several major pectate lyase isozymes secreted by the type H system; and PeIL, one of several secondary Pels secreted by the type II system. We investigated these factors in E. chrysanthemi EC16 with respect to the effects of medium composition and growth phase on gene expression (as determined with uidA fusions and Northern analyses) and effects on virulence. pelE was induced by polygalacturonic acid, but pelL was not, and hrpN was expressed unexpectedly in nutrient-rich King's medium B and in minimal salts medium at neutral pH. In contrast, the effect of medium composition on hrp expression in E. chrysanthemi CUCPB1237 and 3937 was like that of many other phytopathogenic bacteria in being repressed in complex media and induced in acidic pH minimal medium. Northern blot analysis of hrpN and hrpL expression by the wild-type and hrpL::OmegaCm(r) and hrpS::OmegaCm(r) mutants revealed that hrpN expression was dependent on the HrpL alternative sigma factor, whose expression, in turn, was dependent on the HrpS putative sigma(54) enhancer binding protein. The expression of pelE and hrpN increased strongly in late logarithmic growth phase. To test the possible role of quorum sensing in this expression pattern, the expI/expR locus was cloned in Eschetichia coli on the basis of its ability to direct production of acyl-homoserine lactone and then used to construct expI mutations in pelE::uidA, pelL::uidA, and hrpN::uidA Erwinia chrysanthemi strains. Mutation of expI had no apparent effect on the growth-phase-dependent expression of hrpN and pelE, or on the virulence of E. chrysanthemi in wit-loof chicory leaves. Overexpression of hrpN in E. chrysanthemi resulted in approximately 50% reduction of lesion size on chicory leaves without an effect on infection initiation.