Department of Entomology and Plant Pathology, Auburn University, Auburn, Alabama, USA.
Department of Plant Pathology, University of Florida, Gainesville, Florida, USA.
Appl Environ Microbiol. 2019 Oct 1;85(20). doi: 10.1128/AEM.00885-19. Print 2019 Oct 15.
is the predominant pathogen responsible for bacterial leaf spot of tomato and for that of pepper in the southeast United States. Previous studies have indicated significant changes in the population collected from Florida tomato fields over the span of 2 decades, including a shift in race and diversification into three phylogenetic groups driven by genome-wide homologous-recombination events derived from In our sampling of strains associated with bacterial spot disease in Alabama, we were readily able to isolate from symptomatic pepper plants grown in several Alabama counties, indicating a recent shift in the host range of the pathogen. To investigate the diversity of these pepper-pathogenic strains and their relation to populations associated with tomatoes grown in the southeast United States, we sequenced the genomes of eight strains isolated from tomatoes and peppers grown in Alabama and compared them with previously published genome data available from GenBank. Surprisingly, reconstruction of the core genome revealed the presence of two novel genetic groups in Alabama that each harbored a different transcription activation-like effector (TALE). While one TALE, AvrHah1, was associated with an emergent lineage pathogenic to both tomato and pepper, the other was identified as a new class within the AvrBs3 family, here designated PthXp1, and was associated with enhanced symptom development on tomato. Examination of patterns of homologous recombination across the larger species complex revealed a dynamic pattern of gene flow, with multiple donors of spp. associated with diverse hosts of isolation. Bacterial leaf spot of tomato and pepper is an endemic plant disease with a global distribution. In this study, we investigated the evolutionary processes leading to the emergence of novel lineages identified in Alabama. While one lineage was isolated from symptomatic tomato and pepper plants, confirming the host range expansion of , the other lineage was isolated from tomato and acquired a novel transcription activation-like effector, here designated PthXp1. Functional analysis of PthXp1 indicated that it does not induce -mediated resistance in tomato and contributes to virulence, providing an adaptive advantage to strains on tomato. Our findings also show that different phylogenetic groups of the pathogen have experienced independent recombination events originating from multiple species. This suggests a continuous gene flux between related xanthomonads associated with diverse plant hosts that results in the emergence of novel pathogen lineages and associated phenotypes, including host range.
是导致美国东南部番茄细菌性叶斑病和辣椒细菌性叶斑病的主要病原体。先前的研究表明，在过去的 20 年里，从佛罗里达州番茄田中采集的种群发生了显著变化，包括由源自全基因组同源重组事件的三个进化群的种族转变和多样化，这些重组事件来自于。在我们对阿拉巴马州与细菌性斑点病相关的菌株进行采样时，我们很容易从阿拉巴马州几个县种植的有症状的辣椒植株中分离出，表明该病原体的宿主范围最近发生了变化。为了研究这些辣椒致病性菌株的多样性及其与在美国东南部种植的番茄相关种群的关系，我们对从阿拉巴马州种植的番茄和辣椒中分离出的 8 株 进行了测序，并将其与从 GenBank 获得的先前公布的基因组数据进行了比较。令人惊讶的是，对 核心基因组的重建揭示了阿拉巴马州存在两个新的遗传群体，每个群体都含有不同的转录激活样效应物（TALE）。虽然一个 TALE，AvrHah1，与对番茄和辣椒均具有致病性的新兴谱系有关，但另一个则被鉴定为 AvrBs3 家族中的一个新类群，在这里被指定为 PthXp1，并与番茄上增强的症状发展有关。对更大的 种间复杂系统中同源重组模式的研究揭示了基因流动的动态模式，多种 spp.的供体与不同的宿主分离有关。番茄和辣椒细菌性叶斑病是一种具有全球分布的地方性植物疾病。在这项研究中，我们研究了导致在阿拉巴马州发现的新型 谱系出现的进化过程。虽然一个谱系是从有症状的番茄和辣椒植株中分离出来的，证实了 的宿主范围扩大，但另一个谱系是从番茄中分离出来的，并获得了一种新型的转录激活样效应物，在这里被指定为 PthXp1。PthXp1 的功能分析表明，它不会在番茄中诱导 介导的抗性，并有助于毒力，为番茄上的菌株提供了适应优势。我们的研究结果还表明，病原体的不同进化群经历了源自多个 物种的独立重组事件。这表明与不同植物宿主相关的相关黄单胞菌之间存在持续的基因流动，导致新型病原体谱系的出现和相关表型的出现，包括宿主范围。
