Robert P. Ryan,2 and
J. Maxwell Dow1
1Department of Microbiology, Biosciences Institute, University College Cork, Cork, Ireland; 2Division of Molecular Microbiology, College of Life Sciences, University of Dundee, Dundee, U.K.; 3Department of Proteome and Metabolome Research, Faculty of Biology, Bielefeld University, Bielefeld, Germany; 4State Key Laboratory for Conservation and Utilization of Subtropical Agro-bioresources, and College of Life Science and Technology, Guangxi University, Nanning, People's Republic of China
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Accepted 27 June 2013.
The black rot pathogen Xanthomonas campestris utilizes molecules of the diffusible signal factor (DSF) family as signals to regulate diverse processes contributing to virulence. DSF signal synthesis and transduction requires proteins encoded by the rpf gene cluster. RpfF catalyzes DSF synthesis, whereas the RpfCG two-component system links the perception of DSF to alteration in the level of the second messenger cyclic di-GMP. As this nucleotide can exert a regulatory influence at the post-transcriptional and post-translational levels, we have used comparative proteomics to identify Rpf-regulated processes in X. campestris that may not be revealed by transcriptomics. The abundance of a number of proteins was altered in rpfF, rpfC, or rpfG mutants compared with the wild type. These proteins belonged to several functional categories, including biosynthesis and intermediary metabolism, regulation, oxidative stress or antibiotic resistance, and DNA replication. For many of these proteins, the alteration in abundance was not associated with alteration in transcript level. A directed mutational analysis allowed us to describe a number of new virulence factors among these proteins, including elongation factor P and a putative outer membrane protein, which are both widely conserved in bacteria.
© 2013 The American Phytopathological Society