Genetic organization of the hrp gene cluster and dspAE/BF operon in Erwinia herbicola pv. gypsophilae

Erwinia herbicola pv. gypsophilae induces gall formation in gypsophila that is dependent on the existence of a pathogenicity plasmid (pPATH(Ehg)). We previously demonstrated the presence of several hrp genes on this plasmid, By employing transposon mutagenesis and sequencing, a functional hrp gene c luster on the pPATH(Ehg) has now been characterized completely. The hrp gen es of E. herbicola pv. gypsophilae are remarkably similar to and colinear w ith those of Erwinia amylovora and Pantoea stewartii and generally showed 6 0 to 90% nucleotide or deduced amino acid identity. E. herbicola pv. gypsop hilae, however, lacks hrpW, which is present in E. amylovora, Additionally, E, herbicola pv, gypsophilae mutants deficient in harpin production retain ed pathogenicity and were slightly reduced in their ability to elicit a hyp ersensitive response (HR) in tobacco. The "disease specific" region, dspA/E B/F, exhibited 60 to 74% identity with the dspA/EB/F loci of E. amylovora a nd P. stewartii, respectively. Mutations in dspA/E abolished pathogenicity of E, herbicola pv. gypsophilae but not IIR elicitation on tobacco. Inactiv ation of HrpL reduced plant-induced transcription of dspA/E by three orders , indicating Hrp-dependent regulation.