Abstract
SummaryThe 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.
Highlights
Xanthomonads are Gram-negative bacteria that are known to cause disease in a range of important crops worldwide
Studies have revealed many mechanisms that are important for disease and environmental adaptation, including extracellular enzymes, extracellular polysaccharides (EPS), diffusible signal factor (DSF)-dependent cell–cell signalling, and proteins secreted by the type II secretion system (T2SS), type III secretion system (T3SS), type IV secretion system (T4SS) and more recently type VI secretion system (T6SS) (He and Zhang, 2008; Büttner and Bonas, 2010; Ryan et al, 2011, 2015; Notti and Stebbins, 2016; Zhou et al, 2017)
In our earlier work aimed at establishing a general view of the factors that contribute to pathogenicity in Xanthomonas campestris pv. campestris (Xcc), we screened a series of mutants which were constructed using a suicide vector strategy (Windgassen et al, 2000)
Summary
Xanthomonads are Gram-negative bacteria that are known to cause disease in a range of important crops worldwide. Xcc is an important model for the study of microbe–plant interactions because of its genetic tractability and cultivability. For these reasons, the study of Xcc has provided a lot of insight into how plant pathogens can adapt to the host environment and cause disease. In Xcc, one of the best-studied mechanisms that contributes to virulence is the T3SS apparatus This complex system is encoded by over 20 hypersensitive response and pathogenicity (hrp) genes that when silenced lead to the loss of Xcc’s ability to cause full virulence and hypersensitive response (HR) induction (Alfano and Collmer, 1997; Lindgren, 1997). The activation of hrp genes, as well as some genes that encode secreted effector proteins, is controlled by two main regulators: HrpG (OmpR family regulator) and HrpX (AraC-type transcriptional activator) (Huang et al, 2009; Koebnik et al, 2006; Wengelnik et al, 1996; Wengelnik and Bonas, 1996)
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