Pseudomonas syringae pv. actinidiae is a phytopathogen that causes devastating bacterial canker in kiwifruit. Among five biovars defined by genetic, biochemical, and virulence traits, P. syringae pv. actinidiae biovar 3 (Psa3) is the most aggressive and is responsible for the most recent reported outbreaks; however, the molecular basis of its heightened virulence is unclear. Therefore, we designed the first P. syringae multistrain whole-genome microarray, encompassing biovars Psa1, Psa2, and Psa3 and the well-established model P. syringae pv. tomato, and analyzed early bacterial responses to an apoplast-like minimal medium. Transcriptomic profiling revealed i) the strong activation in Psa3 of all hypersensitive reaction and pathogenicity (hrp) and hrp conserved (hrc) cluster genes, encoding components of the type III secretion system required for bacterial pathogenicity and involved in responses to environmental signals; ii) potential repression of the hrp/hrc cluster in Psa2; and iii) activation of flagellum-dependent cell motility and chemotaxis genes in Psa1. The detailed investigation of three gene families encoding upstream regulatory proteins (histidine kinases, their cognate response regulators, and proteins with diguanylate cyclase or phosphodiesterase domains) indicated that cyclic di-GMP may be a key regulator of virulence in P. syringae pv. actinidiae biovars. The gene expression data were supported by the quantification of biofilm formation. Our findings suggest that diverse early responses to the host apoplast, even among bacteria belonging to the same pathovar, can lead to different virulence strategies and may explain the differing outcomes of infections. Based on our detailed structural analysis of hrp operons, we also propose a revision of hrp cluster organization and operon regulation in P. syringae.

Copyright © 2021 The Author(s). This is an open access article distributed under the CC BY-NC-ND 4.0 International license.

丁香假单胞菌（Pseudomonas syringae） pv。猕猴桃是一种植物病原体，会导致猕猴桃的毁灭性细菌性溃疡病。在遗传，生化和毒力特性定义的五个生物变种中，丁香假单胞菌PV。藤梨生化型3（PSA3）是最积极的，负责最新疫情报告; 但是，其毒力增强的分子基础尚不清楚。因此，我们设计了首个丁香假单胞菌多菌株全基因组微阵列，涵盖了生物变种Psa1，Psa2和Psa3，以及成熟的丁香假单胞菌pv模型。番茄，并分析了细菌对质外体样基本培养基的早期细菌反应。转录组分析显示：i）所有过敏反应和致病性（hrp）和hrp保守（hrc）簇基因均在Psa3中强烈激活，这些基因编码细菌致病性所需的III型分泌系统成分，并参与对环境信号的反应；ii）对hrp / hrc的潜在抑制群集在Psa2中；iii）激活Psa1中鞭毛依赖的细胞运动性和趋化性基因。对三个编码上游调节蛋白（组氨酸激酶，它们的同源反应调节剂以及具有双鸟苷酸环化酶或磷酸二酯酶结构域的蛋白）的基因家族的详细研究表明，环状双GMP可能是丁香假单胞菌pv中毒力的关键调节剂。猕猴桃生物变种。基因表达数据得到生物膜形成的定量支持。我们的发现表明，即使对属于同一病原菌的细菌，对宿主质外体的早期反应也不同，可能导致不同的毒力策略，并可能解释不同的感染结果。根据我们对hrp的详细结构分析操纵子，我们还建议修订丁香假单胞菌中的hrp簇组织和操纵子调控。

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