Characterization of an Insertion Sequence Element Associated with Genetically Diverse Plant Pathogenic Streptomyces spp

Abstract

ABSTRACT Streptomycetes are common soil inhabitants, yet few described species are plant pathogens. While the pathogenicity mechanisms remain unclear, previous work identified a gene, nec1 , which encodes a putative pathogenicity or virulence factor. nec1 and a neighboring transposase pseudogene, ORF tnp , are conserved among unrelated plant pathogens and absent from nonpathogens. The atypical GC content of nec1 suggests that it was acquired through horizontal transfer events. Our investigation of the genetic organization of regions adjacent to the 3′ end of nec1 in Streptomyces scabies 84.34 identified a new insertion sequence (IS) element, IS 1629 , with homology to other IS elements from prokaryotic animal pathogens. IS 1629 is 1,462 bp with 26-bp terminal inverted repeats and encodes a putative 431-amino-acid (aa) transposase. Transposition of IS 1629 generates a 10-bp target site duplication. A 77-nucleotide (nt) sequence encompassing the start codon and upstream region of the transposase was identified which could function in the posttranscritpional regulation of transposase synthesis. A functional copy of IS 1629 from S. turgidiscabies 94.09 (Hi-C-13) was selected in the transposon trap pCZA126, through its insertion into the λ cI 857 repressor. IS 1629 is present in multiple copies in some S. scabies strains and is present in all S. acidiscabies and S. turgidiscabies strains examined. A second copy of IS 1629 was identified between ORF tnp and nec1 in S. acidiscabies strains. The diversity of IS 1629 hybridization profiles was greatest within S. scabies . IS 1629 was absent from the 27 nonpathogenic Streptomyces strains tested. The genetic organization and nucleotide sequence of the nec1 -IS 1629 region was conserved and identical among representatives of S. acidiscabies and S. turgidiscabies . These findings support our current model for the unidirectional transfer of the ORF tnp-nec1 -IS 1629 locus from IS 1629 -containing S. scabies (type II) to S. acidiscabies and S. turgidiscabies .