What does it take to be a plant pathogen: genomic insights from Streptomyces species

Abstract

Plant pathogenicity is rare in the genus Streptomyces, with only a dozen or so species possessing this trait out of the more than 900 species described. Nevertheless, such species have had a significant impact on agricultural economies throughout the world due to their ability to cause important crop diseases such as potato common scab, which is characterized by lesions that form on the potato tuber surface. All pathogenic species that cause common scab produce a family of phytotoxins called the thaxtomins, which function as cellulose synthesis inhibitors. In addition, the nec1 and tomA genes are conserved in several pathogenic streptomycetes, the former of which is predicted to function in the suppression of plant defense responses. Streptomyces scabies is the oldest plant pathogen described and has a world-wide distribution, whereas species such as S. turgidiscabies and S. acidiscabies are believed to be newly emergent pathogens found in more limited geographical locations. The genome sequence of S. scabies 87-22 was recently completed, and comparative genomic analyses with other sequenced microbial pathogens have revealed the presence of additional genes that may play a role in plant pathogenicity, an idea that is supported by functional analysis of one such putative virulence locus. In addition, the availability of multiple genome sequences for both pathogenic and nonpathogenic streptomycetes has provided an opportunity for comparative genomic analyses to identify the Streptomyces pathogenome. Such genomic analyses will contribute to the fundamental understanding of the mechanisms and evolution of plant pathogenicity and plant-microbe biology within this genus.

Streptomyces coelicolor Encodes a Urate-Responsive Transcriptional Regulator with Homology to PecS from Plant Pathogens

“…Notably, the pathogenic species for which sequence information is available encode PecS, including the plant pathogens S. ipomoeae, Streptomyces scabiei, Streptomyces acidiscabies, and S. turgidiscabies and the human pathogen Streptomyces somaliensis (31)(32)(33)(34). The pathogenicity of Streptomyces spp.…”

Genome-wide survey of polyketide synthase and nonribosomal peptide synthetase gene clusters in Streptomyces turgidiscabies NBRC 16081

“…STTGS_ 50_ 00290 and STTGS_ 50_ 00280 were characterized as TxtA and TxtB, respectively, which catalyze the synthesis of the cellulose-synthesis-inhibiting virulence factor thaxtomin (Healy et al, 2000) and were reported to exist in many phytopathogenic Streptomyces species (Bignell et al, 2010a). Of the six NRPS gene clusters, with the exception of the txt cluster, three (STTGS_ 09_ 00680-STTGS_ 09_ 00690, STTGS_ 10_ 01580, and STTGS_ 07_ 02660) showed similarities to NRPSs in S. scabiei 87.22.…”

“…While the presence of a coronafacic acid (CFA)-like biosynthetic cluster and a putative concanamycin biosynthetic cluster within the genome was previously reported (Bignell et al, 2010a, b), the other secondary metabolic gene clusters have not yet been surveyed. Genes from the CFA-like cluster were not detected in S. acidiscabies or S. turgidiscabies, and these two species also did not produce concanamycins (Bignell et al, 2010a). These results suggested that secondary metabolic gene clusters, except for txtABCD, found in S. scabiei 87.22 do not appear to be well conserved in other Streptomyces species.…”

“…This is the case for S. acidiscabies and S. turgidiscabies, which have emerged independently over recent years in the United States and Japan. The comparison of genes related to pathogenicity among S. scabiei, S. acidiscabies and S. turgidiscabies has been well studied to date (Bignell et al, 2010a;Bukhalid et al, 2002;Kers et al, 2005).…”

Multi-locus Sequence Analysis

“…The function of most of the Streptomyces pathogenome has still to be resolved but it does include genes spread through HGT that encode secreted proteins, transcriptional regulators and membrane transporters, as well as for secondary metabolite biosynthesis (Loria, Kers, & Joshi, 2006;Bignell, Huguet-Tapia, Joshi, Pettis, & Loria, 2010). S. acidiscabies and S. turgidiscabies are thought to be newly emergent pathogens with a limited geographical distribution.…”