Rodrigo P. P. Almeida,1
Karyn L. Newman,3
Michael Ionescu,3 and
Steven E. Lindow3
1Department of Environmental Science, Policy, and Management, University of California, Berkeley 94720, U.S.A.; 2Department of Entomology and Nematology, Citrus Research and Education Center, University of Florida, Lake Alfred 33850, U.S.A.; 3Department of Plant and Microbial Biology, University of California, Berkeley; 4Centre for DNA Fingerprinting and Diagnostics, Hyderabad 500001, India
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Accepted 9 December 2011.
In Xylella fastidiosa the fatty acid signal molecule diffusible signaling factor (DSF) is produced and sensed by components of the regulation of pathogenicity factors (rpf) cluster; lack of DSF production in RpfF mutants results in a non-vector-transmissible phenotype yet cells are hypervirulent to grape. rpfB has not been characterized in Xylella fastidiosa, although its homolog has been suggested to be required for DSF synthesis in Xanthomonas campestris pv. campestris. We show that RpfB is involved in DSF processing in both Xylella fastidiosa and Xanthomonas campestris, affecting the profile of DSF-like fatty acids observed in thin-layer chromatography. Although three fatty acids whose production is dependent on RpfF were detected in Xylella fastidiosa and Xanthomonas campestris wild-type strains, their respective rpfB mutants accumulated primarily one chemical species. Although no quantifiable effect of rpfB on plant colonization by Xylella fastidiosa was found, insect colonization and transmission was reduced. Thus, RpfB apparently is involved in DSF processing, and like Xanthomonas campestris, Xylella fastidiosa also produces multiple DSF molecules. It is possible that Xylella fastidiosa coordinates host vector and plant colonization by varying the proportions of different forms of DSF signals via RpfB.
© 2012 The American Phytopathological Society