C1: The role of selected RNA-binding proteins and small RNAs in bacterial pathogenicity

Supervisor: Prof. Dr. Ulla Bonas


Specific aim(s)/topic(s)

(1) The role of RNA-binding proteins in Xanthomonas virulence

(2) The role of selected small RNAs in Xanthomonas virulence


Background and significance

The interaction between the Gram-negative plant pathogenic bacterium Xanthomonas campestris pv. vesicatoria (Xcv) and its host plants pepper and tomato represents a well-studied model system. While pathogenicity of Xcv depends on the type III secretion system (T3SS), there are additional virulence factors that modulate the interaction of xanthomonads with their host plants, e.g., secreted enzymes. Since virulence of many bacterial animal and human pathogens is regulated by small non-coding RNAs (sRNAs), we aimed at the identification and analysis of sRNAs in Xcv.  Using a dRNA-seq approach, we have identified 24 sRNAs in Xcv strain 85-10. Two selected sRNAs were found to contribute to the outcome of infection, i.e., deletion of the corresponding sRNA gene strongly delayed disease symptoms in susceptible plants and the induction of the hypersensitive response (HR) in resistant plants. The HR is a rapid localized plant cell death at the infection site, resulting in a halt of pathogen ingress. It is known for enteropathogenic human pathogens that sRNA function often depends on RNA-binding proteins (RBPs). We therefore analyzed Hfq and CsrA, two highly conserved RBPs in bacteria. Knock-out of hfq had no obvious effect, whereas the deletion of csrA in Xcv affects bacterial growth both in culture and in planta. Our study is the first comprehensive analysis of sRNAs and RBPs in a plant pathogenic bacterium and awaits the identification of the mRNA targets to understand the role of these molecules in bacterial virulence.