Molecular Characterization of the Pseudomonas Syringae hrp hrm Gene Cluster.

了解植物中细菌致病的分子基础的关键是植物防御激发子和寄主范围决定因素的产生和部署。我们已经证明了从丁香假单胞菌中分离到的hrp/hrm基因簇。紫丁香61使非致病细菌能够诱导植物防御。因此，HRP/HRM基因簇似乎构成了足以产生植物防御激发子的最小遗传单位。在该组内确定了14个明显的跨国单位，这些单位被组织为9个明显的转录单位。几个HRP基因作为积极的调节元件。本项目的总体目标是阐明特定的hrp/hrm基因在确定丁香疫霉菌株的致病性和寄主范围方面的作用。我们的方法是：1)获得该簇其余部分的核苷酸序列，以便于以后的操作、与其他细菌的比较分析和基因功能的推断；2)表征控制HRP基因表达的调节级联，以便能够识别和操纵直接参与植物防御激发子产生的基因；以及3)进行基因替换实验，以测试特定的HRP基因在确定致病性和寄主范围方面的作用。对这些基因的研究应该会带来有用的技术，以阻止对易受细菌感染的植物的损害。

A key to understanding the molecular basis for bacterial pathogenicity in plants is the production and deployment of plant defense elicitors and host range determinants. We have previously shown that the hrp/hrm gene cluster isolated from Pseudomonas syringae pv. syringae 61 enables nonpathogenic bacteria to elicit plant defenses. The hrp/hrm gene cluster, therefore, appears to constitute a minimum genetic unit sufficient to produce plant defense elicitors. Fourteen apparent transnational units have been identified within the cluster that are organized as nine apparent transcriptional units. Several hrp genes act as positive regulatory elements. The overall goal of this project is to elucidate the role of specific hrp/hrm genes in determining the pathogenicity and host range of P. syringae strains. Our approach will be to: 1) obtain the nucleotide sequence for remaining portions of the cluster to facilitate later manipulation, comparative analyses with other bacteria and deduction of gene function; 2) characterize the regulatory cascade controlling expression of hrp genes so that the genes directly contributing to the production of plant defense elicitors can be identified and manipulated; and 3) perform gene replacement experiments to test the role of specific hrp genes in determining pathogenicity and host range. %%% The study of these genes should lead to techniques useful in stopping the damage to plants susceptible to bacterial infection.