Submitted to: Molecular Microbiology
Publication Type: Peer reviewed journal
Publication Acceptance Date: 2/5/2005
Publication Date: 4/1/2005
Citation: Kers, J.A., Cameron, K.D., Joshi, M.V., Bukhalid, R.A., Morello, J.E., Wach, M.J., Gibson, D.M., Loria, R. 2005. A large, mobile pathogenicity island confers plant pathogenicity on streptomyces species. Molecular Microbiology. 55(4):1025-1033. Interpretive Summary: Several Streptomyces species cause "scab" diseases on potato tubers, sweet potato storage roots and expanded tap roots of radish, beet and similar crops. All of these species produce a family of toxins known as thaxtomins that are critical for pathogenicity. In previous work, we identified the genes responsible for toxin production, along with other genes that seem to be involved in virulence. In this paper, we have identified a large DNA fragment known as a pathogenicity island that is common to all plant pathogenic Streptomyces. When this DNA fragment was introduced into two nonpathogenic Streptomyces species, it conferred pathogenicity to one of the organisms. This pathogenicity island is the first to be described in a gram positive plant pathogenic bacterium and provides an explanation as to how new plant pathogenic Streptomyces species may emerge.
Technical Abstract: Potato scab disease is a globally important disease caused by polyphyletic plant pathogenic Streptomyces spp. Streptomyces acidiscabies, S. scabies, and S. turgidiscabies possess a conserved biosynthetic pathway for the nitrated dipeptide phytotoxin thaxtomin. These pathogens also possess the nec1 gene which encodes a necrogenic protein that is an independent virulence factor. In this paper we describe a large (325-660 kb) pathogenicity island (PAI) conserved among these three plant pathogenic Streptomyces species. A partial DNA sequence of this PAI revealed the thaxtomin biosynthetic pathway, nec1, a putative tomatinase gene, and many mobile genetic elements. In addition, the PAI from S. turgidiscabies contains a plant fasciation (fas) operon homologous to and collinear with the fas operon in the plant pathogen Rhodococcus fascians. The PAI was mobilized during mating from S. turgidiscabies to the nonpathogens S. coelicolor and S. diastatochromogenes on a 660 kb DNA element and integrated site-specifically into a putative integral membrane lipid kinase. Acquisition of the PAI conferred a pathogenic phenotype on S. diastatochromogenes but not on S. coelicolor. This PAI is the first to be described in a Gram-positive plant pathogenic bacterium and is responsible for the emergence of new plant pathogenic Streptomyces species in agricultural systems.