The Hrp pathogenicity island of Erwinia amylovora and identification of three novel genes required for systemic infection‡

Abstract

SUMMARY Sequence analysis of the region bordering the hrp/dsp gene cluster of Erwinia amylovora strain Ea321, which causes fire blight, revealed characteristics of pathogenicity islands (PAIs). Included are genes for a phage integrase, a tRNA(Phe), several orthologues of genes of YAPI, a PAI of Yersinia pseudotuberculosis, and several putative virulence genes with HrpL-dependent promoter motifs. The island is designated the Hrp PAI of E. amylovora. It is comprised of a chromosomal region of c. 62 kb with 60 open reading frames (ORFs). Comparison of the Hrp PAI of E. amylovora with those of four closely related bacteria showed that orfB, a homologue of avrBsT of Xanthomonas campestris pv. vesicatoria, and orfA, its putative chaperone gene, are present only in the Hrp PAI of E. amylovora. As regions flanking the hrp/dsp gene cluster are quite diverse, addition and deletion may have occurred during divergent evolution of the five bacteria. Among ORFs of the PAI of Ea321, three new HrpL-dependent genes were identified. Because they are required for full virulence in apple, they were designated hsvC, hsvB and hsvA (hrp-associated systemic virulence). They encode a homologue of an amidinotransferase for phaseolotoxin biosynthesis and homologues of a nikkomycin-biosynthetic protein of Pseudomonas syringae.

Phylogenetic evidence for extensive horizontal gene transfer of type III secretion system genes among enterobacterial plant pathogens

“…The four genes used to construct the phylogenies presented in this study are integral components of the needle complex, interacting with both the bacterial cell membranes and the chaperone-effector molecules secreted into the host cells. (b) Schematic representation of the characterized hrp/hrc operons as described for Erwinia amylovora (Oh et al, 2005). For visual clarity, oblique lines were added to the figure to denote the removal of T3SS chromosomal segments not related to the four hrc genes analysed here.…”

“…Conversely, they appear to have been integrated into the bacterial genomes of their enterobacterial plant pathogenic counterparts (Hacker et al, 1997;Oh et al, 2005;Toth et al, 2006). The pathogenicity island of Erwinia amylovora, which has been recently characterized (Oh et al, 2005), consists of a 62 kb region with 60 ORFs. A region of approximately 22 kb encodes the proteins of the T3SS in three operons: hrpA, hrpC and hrpJ ( Fig.…”

“…A region of approximately 22 kb encodes the proteins of the T3SS in three operons: hrpA, hrpC and hrpJ ( Fig. 1b; Oh et al, 2005).…”

“…To understand the role of horizontal gene transfer (HGT) of T3SS genes among the enterobacterial plant pathogens, we analysed sequences from four genes, hrcC, hrcR, hrcJ and hrcV. These four genes represent each of the three characterized operons (Oh et al, 2005), and encode proteins which serve different functional purposes (Fig. 1b).…”

Secretion and translocation signals and DspB/F-binding domains in the type III effector DspA/E of Erwinia amylovora

“…amylovora, namely OrfA and OrfC (Oh et al, 2005), was examined. Although neither OrfA nor OrfC bound the Nterminal 250 amino acids of DspA/E, OrfA bound the Cterminal 1059 amino acids of DspA/E (Fig.…”