Induction of Plant Resistance Reactions by Pseudomonas syringae

植物防止潜在致病微生物定植的主要机制是过敏反应（hypersensitive response， HR），这是一种快速的局部坏死，伴随着抗菌化合物的产生。先前对丁香假单胞菌病原菌（丁香假单胞菌的宿主范围变种）的遗传研究表明，不相容的细菌病原体对HR的激发受两种基因控制：hrp（任何植物反应所必需的）和avr（影响宿主范围的）。引发子的性质尚不清楚。丁香假单胞菌与烟草悬浮培养细胞的相互作用为研究细菌对HR的吸收提供了一个理想的系统。培养的烟草细胞通过K+外排/H+内流交换反应（XR）对不相容细菌迅速作出反应，该反应在生理、遗传和发育上与植物中的HR相似。在迄今为止的研究中，本实验室已经：1)从丁香p.s ringae pv中克隆了一组明显的hrp/avr基因。syringae (Pss61)，在腐生菌、大肠杆菌和荧光假单胞菌中表型表达，从而简化了随后的遗传分析；2)观察到含有野生型hrp/avr基因的Pss61比野生型Pss61产生更强的XR，表明可以通过基因操作提高激发子的产生；3)确定体外预诱导XR细菌引发子的条件。这些发现为研究控制宿主范围和致病性的细菌信号提供了强有力的新工具。本研究的目的是分离和生物化学表征参与诱导植物反应的细菌激发子。提出的实验将确定hrp/avr克隆中存在的遗传单位，并使用报告基因融合来阐明功能位点的调控并表征其特征蛋白质产品。* * * / /

A primary mechanism through which plants prevent colonization by potentially pathogenic microorganisms is the hypersensitive response (HR), a rapid, local necrosis accompanied by the production of antimicrobial compounds. Previous genetic studies with Pseudomonas syringae pathovars (host range variants of P.syringae) suggest that elicitation of the HR by incompatible bacterial pathogens is controlled by two types of genes: hrp (necessary for any plant reaction) and avr (affecting host range). The nature of the elicitor(s) remains unknown. The interaction of P.syringae with tobacco suspension culture cells provides an ideal system to investigate the elicitation of the HR by bacteria. Cultured tobacco cells rapidly respond to incompatible bacteria by a K+ efflux/H+ influx exchange response (XR) that is physiologically, genetically and developmentally similar to the in planta HR. In studies thus far this lab has: 1) cloned an apparent set of hrp/avr genes from P.syringae pv. syringae (Pss61) that are phenotypically expressed in the saprophytes, Escherichia coli and P. fluorescens, thus simplifying subsequent genetic analyses; 2) observed that Pss61 containing the cloned wild-type hrp/avr genes produce a stronger XR than wild-type Pss61, suggesting that elicitor production can be enhanced by genetic manipulation; and 3) identified in vitro conditions for preinducing the bacterial elicitor of the XR. These findings provide powerful new tools to investigate the bacterial signals governing host range and pathogenicity. The goal of this investigation is to isolate and characterize biochemically the bacterial elicitors involved in the induction of plant responses. The proposed experiments will define the genetic units present in the hrp/avr clone and use reporter gene fusions to elucidate the regulation of functional loci and characterize the protein products.***//