Department of Plant Pathology and Microbiology, Iowa State University, Ames, IA 50011, USA.
Proc Natl Acad Sci U S A. 2013 Jan 29;110(5):E425-34. doi: 10.1073/pnas.1221892110. Epub 2013 Jan 14.
Some strains of the foliar pathogen Pseudomonas syringae are adapted for growth and survival on leaf surfaces and in the leaf interior. Global transcriptome profiling was used to evaluate if these two habitats offer distinct environments for bacteria and thus present distinct driving forces for adaptation. The transcript profiles of Pseudomonas syringae pv. syringae B728a support a model in which leaf surface, or epiphytic, sites specifically favor flagellar motility, swarming motility based on 3-(3-hydroxyalkanoyloxy) alkanoic acid surfactant production, chemosensing, and chemotaxis,indicating active relocation primarily on the leaf surface. Epiphytic sites also promote high transcript levels for phenylalanine degradation, which may help counteract phenylpropanoid-based defenses before leaf entry. In contrast, intercellular, or apoplastic,sites favor the high-level expression of genes for GABA metabolism (degradation of these genes would attenuate GABA repression of virulence) and the synthesis of phytotoxins, two additional secondary metabolites, and syringolin A. These findings support roles for these compounds in virulence, including a role for syringolin A in suppressing defense responses beyond stomatal closure. A comparison of the transcriptomes from in planta cells and from cells exposed to osmotic stress, oxidative stress, and iron and nitrogen limitation indicated that water availability, in particular,was limited in both leaf habitats but was more severely limited in the apoplast than on the leaf surface under the conditions tested. These findings contribute to a coherent model of the adaptations of this widespread bacterial phytopathogen to distinct habitats within its host.
一些叶生病原菌丁香假单胞菌菌株适应在叶片表面和叶片内部生长和存活。全局转录组分析用于评估这两个栖息地是否为细菌提供了不同的环境，从而为适应提供了不同的驱动力。丁香假单胞菌 pv. syringae B728a 的转录谱支持这样一种模式，即叶面或附生部位特异性地有利于鞭毛运动、基于 3-(3-羟基烷酰氧基)烷酸表面活性剂产生的群集运动、化学感应和趋化性，表明主要在叶片表面上进行积极的重新定位。附生部位还促进苯丙氨酸降解的高转录水平，这可能有助于在进入叶片之前抵消基于苯丙烷的防御。相比之下，细胞间或质外体部位有利于 GABA 代谢（降解这些基因会减弱 GABA 对毒性的抑制）和两种其他次生代谢物以及丁香菌 A 的合成的高水平表达。这些发现支持这些化合物在毒性中的作用，包括丁香菌 A 在抑制超过气孔关闭的防御反应中的作用。对来自植物细胞和暴露于渗透胁迫、氧化应激、铁和氮限制的细胞的转录组的比较表明，在测试条件下，水的可用性，特别是在两种叶片栖息地中受到限制，但在质外体中比在叶片表面上受到的限制更为严重。这些发现有助于建立一个广泛的细菌植物病原菌适应宿主内不同栖息地的连贯模型。
