Flp, a Fis‐like protein, contributes to the regulation of type III secretion and virulence processes in the phytopathogen Xanthomonas campestris pv. campestris

Abstract

Summary The ability of the plant pathogen Xanthomonas campestris pv. campestris ( Xcc ) to cause disease is dependent on its ability to adapt quickly to the host environment during infection. Like most bacterial pathogens, Xcc has evolved complex regulatory networks that ensure expression and regulation of their virulence genes. Here, we describe the identification and characterization of a Fis‐like protein (named Flp), which plays an important role in virulence and type III secretion system (T3SS) gene expression in Xcc . Deletion of flp caused reduced virulence and hypersensitive response (HR) induction of Xcc and alterations in stress tolerance. Global transcriptome analyses revealed the Flp had a broad regulatory role and that most T3SS HR and pathogenicity ( hrp ) genes were down‐regulated in the flp mutant. β ‐glucuronidase activity assays implied that Flp regulates the expression of hrp genes via controlling the expression of hrpX . More assays confirmed that Flp binds to the promoter of hrpX and affected the transcription of hrpX directly. Interestingly, the constitutive expression of hrpX in the flp mutant restored the HR phenotype but not full virulence. Taken together, the findings describe the unrecognized regulatory role of Flp protein that controls hrp gene expression and pathogenesis in Xcc .

The HrpG/HrpX Regulon of Xanthomonads—An Insight to the Complexity of Regulation of Virulence Traits in Phytopathogenic Bacteria

“…Expression, stability, and activity of HrpG and HrpX are dependent on numerous regulatory factors. HrpG and HrpX are negatively or positively controlled by two-component system kinases and response regulators [ 60 , 62 ], ATPases [ 102 ], transcriptional regulators [ 53 , 63 , 77 , 81 , 84 , 91 , 93 , 103 , 104 , 105 ], small signaling molecules [ 74 , 101 ] and histone-like nucleoid-structuring (H-NS) protein [ 106 , 107 , 108 ] ( Figure 2 ). However, most studies do not demonstrate direct interactions with HrpG, HrpX, or their promoters and it appears that the regulatory function on this regulon by most of these factors is probably indirect.…”

“…Interestingly, RpoE1 is neither affected transcriptionally by HrpG nor affects the expression of hrpG itself, indicating that its regulatory function is independent of HrpG [ 104 ]. The Xcc fis-type transcriptional regulator Flp positively regulates virulence, exoenzyme production, growth in complex media, motility, and hrp gene expression [ 105 ] ( Figure 2 ). In vivo and in vitro DNA-protein analyses combined with transcriptional data demonstrate that Flp interacts with the hrpX promoter and regulates its expression, suggesting direct regulation of hrpX transcription by Flp [ 105 ] ( Figure 3 ).…”

“…The Xcc fis-type transcriptional regulator Flp positively regulates virulence, exoenzyme production, growth in complex media, motility, and hrp gene expression [ 105 ] ( Figure 2 ). In vivo and in vitro DNA-protein analyses combined with transcriptional data demonstrate that Flp interacts with the hrpX promoter and regulates its expression, suggesting direct regulation of hrpX transcription by Flp [ 105 ] ( Figure 3 ). GamR, a LysR-type galactose metabolism regulator, was reported to regulate hrpG and hrpX in plant-mimicking media [ 77 ].…”

PilG and PilH antagonistically control flagellum-dependent and pili-dependent motility in the phytopathogen Xanthomonas campestris pv. campestris

“…Bacterial in planta growth was tested as previously described [42]. The strains were grown in the NYG medium for overnight and diluted to OD 600 of 0.001, and then inoculated to Chinese radish by leaf-clipping.…”

A HU‐like protein is required for full virulence in Xanthomonas campestris pv. campestris

“…In addition to their roles in maintaining bacterial chromosome architecture and regulating DNA transactions such as recombination and DNA replication, there is an increasing body of work describing how NAPs or their homologues also play important roles in gene regulation. For example, Fis is involved in controlling the expression of virulence factors in a number of pathogens (Duprey et al, 2014;Leng et al, 2019;Lv et al, 2018), where it regulates gene expression by modulating the level of DNA supercoiling in the cell and interacting with RNA polymerase at the position of its binding site (Dillon & Dorman, 2010). HU regulates the expression of hundreds of genes across the whole genome in E. coli by remodelling bacterial nucleoids, modulating the 3D arrangement of DNA, facilitating DNA looping in a promoter region, trapping free supercoils, indirectly altering supercoiling through DNA topoisomerases, or cooperating with transcription regulators (Berger et al, 2016;Lioy et al, 2018;Remesh et al, 2020).…”