Bacteria harbour several abundant small DNA-binding proteins known as nucleoid-associated proteins (NAPs) that contribute to the structure of the bacterial nucleoid as well as to gene regulation. Although the function of NAPs as global transcriptional regulators has been comprehensively studied in the model organism Escherichia coli, their regulatory functions in other bacteria remain relatively poorly understood. Xanthomonas campestris pv. campestris (Xcc) is a gram-negative bacterium that causes black rot disease in almost all members of the crucifer family. In previous work, we demonstrated that a Fis homologue protein, which we named Fis-like protein (Flp), contributes to the regulation of virulence, type III secretion, and a series of other phenotypes in Xcc. Here we have examined the role of XC_1355, which is predicted to encode a DNA-binding protein belonging to the HU family herein named HU-like protein (Hlp). We show that mutation of XC_1355 in Xcc reduces the virulence, extracellular polysaccharide production, and cell motility, but has no effect on the production of extracellular enzymes and induction of the hypersensitive response. These data together with transcriptome analysis indicate that hlp is a previously uncharacterized gene involved in virulence that has partially overlapping and complementary functions with flp in Xcc, although the two regulators have opposite effects on the expression of genes involved in type III secretion. The findings add to our understanding of the complex regulatory pathways that act to regulate virulence in Xcc.

中文翻译：

---

Xanthomonas campestris pv 中的完全毒力需要一种 HU 样蛋白。油菜

细菌含有几种丰富的小 DNA 结合蛋白，称为类核相关蛋白 (NAP)，它们有助于细菌类核的结构以及基因调控。尽管 NAP 作为全球转录调节因子的功能已经在模式生物大肠杆菌中得到了全面研究，但它们在其他细菌中的调节功能仍然知之甚少。Xanthomonas campestris pv. 油菜(Xcc) 是一种革兰氏阴性细菌，在十字花科的几乎所有成员中都会引起黑腐病。在之前的工作中，我们证明了一种 Fis 同源蛋白，我们将其命名为 Fis 样蛋白 (Flp)，它有助于调节 Xcc 中的毒力、III 型分泌和一系列其他表型。在这里，我们检查了XC_1355的作用，预计它会编码一种属于 HU 家族的 DNA 结合蛋白，称为 HU 样蛋白 (Hlp)。我们表明Xcc中 XC_1355 的突变降低了毒力、细胞外多糖的产生和细胞运动，但对细胞外酶的产生和过敏反应的诱导没有影响。这些数据与转录组分析一起表明hlp是以前未表征的与毒力有关的基因，它与Xcc中的 flp具有部分重叠和互补的功能，尽管这两种调节剂对参与 III 型分泌的基因的表达具有相反的作用。这些发现增加了我们对调节 Xcc 毒力的复杂调节途径的理解。