BACKGROUND The virulence of the plant pathogen Xanthomonas campestris pv. campestris (Xcc) involves the coordinate expression of many virulence factors, including surface appendages flagellum and type IV pili, which are required for pathogenesis and the colonization of host tissues. Despite many insights gained on the structure and functions played by flagellum and pili in motility, biofilm formation, surface attachment and interactions with bacteriophages, we know little about how these appendages are regulated in Xcc. RESULTS Here we present evidence demonstrating the role of two single domain response regulators PilG and PilH in the antagonistic control of flagellum-dependent (swimming) and pili-dependent (swarming) motility. Using informative mutagenesis, we reveal PilG positively regulates swimming motility while and negatively regulating swarming motility. Conversely, PilH negatively regulates swimming behaviour while and positively regulating swarming motility. By transcriptome analyses (RNA-seq and RT-PCR) we confirm these observations as PilG is shown to upregulate many genes involved chemotaxis and flagellar biosynthesis but these similar genes were downregulated by PilH. Co-immunoprecipitation, bacterial two-hybrid and pull-down analyses showed that PilH and PilG were able to interact with district subsets of proteins that potentially account for their regulatory impact. Additionally, we present evidence, using mutagenesis that PilG and PilH are involved in other cellular processes, including chemotaxis and virulence. CONCLUSIONS Taken together, we demonstrate that for the conditions tested PilG and PilH have inverse regulatory effects on flagellum-dependent and pili-dependent motility in Xcc and that this regulatory impact depends on these proteins influences on genes/proteins involved in flagellar biosynthesis and pilus assembly.

中文翻译：

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PilG和PilH拮抗植物病原体Xanthomonas campestris pv中鞭毛依赖和菌毛依赖的运动。桔梗。

背景技术植物病原体Xanthomonas campestris pv的毒力。campestris（Xcc）涉及许多毒力因子的协同表达，包括表面附属物鞭毛和IV型菌毛，这是发病机理和宿主组织定植所必需的。尽管在鞭毛和菌毛在运动性，生物膜形成，表面附着以及与噬菌体的相互作用中获得了许多结构和功能方面的见识，但我们对Xcc中这些附属物的调控方式知之甚少。结果在这里，我们提供了证明两个单域响应调节剂PilG和PilH在拮抗鞭毛依赖性（游泳）和菌毛依赖性（成群）运动中的作用的证据。利用信息诱变，我们发现PilG正面调节游泳运动，而负面调节游泳运动。相反，PilH消极地调节游泳行为，而积极地调节群体运动。通过转录组分析（RNA-seq和RT-PCR），我们证实了这些观察结果，因为PilG显示出上调了许多与趋化性和鞭毛生物合成有关的基因，但这些相似的基因却被PilH下调。免疫共沉淀，细菌两杂交和下拉分析表明，PilH和PilG能够与蛋白质的区域子集相互作用，这可能解释了它们的调节作用。此外，我们利用诱变技术提供了PilG和PilH参与其他细胞过程（包括趋化性和毒力）的证据。结论综合起来，