沙门氏菌与大肠杆菌分化的一个重要事件是通过水平转移获得沙门氏菌致病性岛1(SPI-1),含有沙门氏菌入侵宿主细胞所需的基因。HilD是SPI-1中的AraC样转录调节因子,可诱导SPI-1和位于沙门氏菌其他基因组区域的许多其他获得性毒力基因的表达。此外,HilD已被证明可以积极控制一些祖先基因(也存在于大肠杆菌和其他细菌中)的表达,包括phoH.在这项研究中,我们确定HilD的获得和顺式调节进化都导致phoH基因整合到HilD调节子中。我们的结果表明,HilD结合序列是在肠球菌血清变型鼠伤寒沙门氏菌phoH基因的调节区中产生的,在SPI-1诱导条件下介导该基因启动子1的激活。此外,我们发现H-NS的压制,组蛋白样蛋白质,也适用于鼠伤寒沙门氏菌phoH基因,并且HilD通过拮抗H-NS部分激活该基因的表达。此外,我们的结果表明,在响应低磷酸盐的情况下,鼠伤寒沙门氏菌基因的表达也被激活,但独立于PhoB/R双组分系统,已知调节大肠杆菌phoH基因以响应低磷酸盐。因此,我们的结果表明,顺式调节进化在HilD调节子的扩展中起作用,并说明了直系同源基因的差异调节现象。重要性介导细菌分化的两种机制是众所周知的:通过水平转移事件获得基因和编码DNA序列中的突变。在这项研究中,我们发现,phoH祖先基因在鼠伤寒沙门氏菌和大肠杆菌之间有差异调节,两个密切相关的细菌物种。我们的结果表明,这种差异调节是通过鼠伤寒沙门氏菌基因的调节序列中的突变以及鼠伤寒沙门氏菌获得编码转录调节因子HilD的外源DNA而产生的。因此,我们的结果,加上越来越多的研究,表明顺式调控进化可以导致转录调控的重新布线和重新编程,这在细菌随时间的发散中也起着重要作用。
One important event for the divergence of Salmonella from Escherichia coli was the acquisition by horizontal transfer of the Salmonella pathogenicity island 1 (SPI-1), containing genes required for the invasion of host cells by Salmonella. HilD is an AraC-like transcriptional regulator in SPI-1 that induces the expression of the SPI-1 and many other acquired virulence genes located in other genomic regions of Salmonella. Additionally, HilD has been shown to positively control the expression of some ancestral genes (also present in E. coli and other bacteria), including phoH. In this study, we determined that both the gain of HilD and cis-regulatory evolution led to the integration of the phoH gene into the HilD regulon. Our results indicate that a HilD-binding sequence was generated in the regulatory region of the S. enterica serovar Typhimurium phoH gene, which mediates the activation of promoter 1 of this gene under SPI-1-inducing conditions. Furthermore, we found that repression by H-NS, a histone-like protein, was also adapted on the S. Typhimurium phoH gene and that HilD activates the expression of this gene in part by antagonizing H-NS. Additionally, our results revealed that the expression of the S. Typhmurium phoH gene is also activated in response to low phosphate but independently of the PhoB/R two-component system, known to regulate the E. coli phoH gene in response to low phosphate. Thus, our results indicate that cis-regulatory evolution has played a role in the expansion of the HilD regulon and illustrate the phenomenon of differential regulation of ortholog genes. IMPORTANCE Two mechanisms mediating differentiation of bacteria are well known: acquisition of genes by horizontal transfer events and mutations in coding DNA sequences. In this study, we found that the phoH ancestral gene is differentially regulated between Salmonella Typhimurium and Escherichia coli, two closely related bacterial species. Our results indicate that this differential regulation was generated by mutations in the regulatory sequence of the S. Typhimurium phoH gene and by the acquisition by S. Typhimurium of foreign DNA encoding the transcriptional regulator HilD. Thus, our results, together with those from an increasing number of studies, indicate that cis-regulatory evolution can lead to the rewiring and reprogramming of transcriptional regulation, which also plays an important role in the divergence of bacteria through time.