State Key Laboratory for Conservation and Utilization of Subtropical Agro-bioresources, College of Life Science and Technology, Guangxi University, 100 Daxue Road, Nanning, 530004, Guangxi, China.
BMC Microbiol. 2020 Feb 18;20(1):37. doi: 10.1186/s12866-020-1712-3.
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.
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.
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.
植物病原菌野油菜黄单胞菌（Xanthomonas campestris pv. campestris，Xcc）的毒力涉及许多毒力因子的协调表达，包括鞭毛和 IV 型菌毛等表面附属物，这些附属物对于病原菌的致病和宿主组织的定植是必需的。尽管我们已经对鞭毛和菌毛在运动、生物膜形成、表面附着和与噬菌体相互作用中的结构和功能有了很多了解，但我们对 Xcc 中这些附属物的调控机制知之甚少。
本文提供了证据，证明了两个单域应答调节蛋白 PilG 和 PilH 在鞭毛依赖性（游动）和菌毛依赖性（泳动）运动的拮抗调控中的作用。通过信息丰富的诱变，我们揭示了 PilG 正向调控游动运动，而负向调控泳动运动。相反，PilH 负向调控游动行为，而正向调控泳动运动。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 显示出许多参与趋化和鞭毛生物合成的基因上调，但这些相似的基因被 PilH 下调。共免疫沉淀、细菌双杂交和下拉分析表明，PilH 和 PilG 能够与潜在解释其调控作用的不同亚组蛋白相互作用。此外，我们还通过诱变提供了证据，证明 PilG 和 PilH 参与了其他细胞过程，包括趋化性和毒力。
综上所述，我们证明了在测试条件下，PilG 和 PilH 对 Xcc 中鞭毛依赖性和菌毛依赖性运动具有相反的调节作用，这种调节作用取决于这些蛋白质对鞭毛生物合成和菌毛组装相关基因/蛋白的影响。
