Disease-specific genes of Erwinia amylovora: keys to understanding pathogenesis and potential targets for disease control.

Abstract

This chapter discusses the discovery and the genetic characterization of a disease-specific (dsp) locus in Erwinia amylovora required for the pathogenesis in host plants but not required for elicitation of defence responses in non-host plants. This dsp locus contains two genes, dspE and dspF, and flanks the hrp gene cluster. The dspEF locus is homologous with the avrE locus of Pseudomonas syringae pv. tomato and functions as a virulence locus when expressed in a pathovar of P. syringae that infects soyabean. The dspE gene product travels the Hrp secretion pathway, apparently in a dspF-dependent manner. A number of other genes with potentially related functions in host specificity and pathogenicity have also been discovered in E. amylovora and in other Erwinia spp. Findings to date carry far-reaching implications regarding the nature and evolution of bacterial effector proteins involved in plant pathogenesis. The broad physical and functional conservation of the dspEF locus renders it a key target for strategies to better understand and to control fire blight and other bacterial diseases of plants.