Streptomyces scabies87-22 Possesses a Functional Tomatinase

Abstract

The actinomycete Streptomyces scabies 87-22 is the causal agent of common scab, an economically important disease of potato and taproot crops. Sequencing of the S. scabies 87-22 genome revealed the presence of a gene with high homology to the gene encoding the ␣-tomatine-detoxifying enzyme tomatinase found in fungal tomato pathogens. The tomA gene from S. scabies 87-22 was cotranscribed with a putative family 1 glycosyl hydrolase gene, and purified TomA protein was active only on ␣-tomatine and not potato glycoalkaloids or xylans. Tomatinase-null mutants were more sensitive to ␣-tomatine than the wild-type strain in a disk diffusion assay. Interestingly, tomatine affected only aerial mycelium and not vegetative mycelium, suggesting that the target(s) of ␣-tomatine is not present during vegetative growth. Severities of disease for tomato seedlings affected by S. scabies 87-22 wild-type and ⌬tomA1 strains were indistinguishable, suggesting that tomatinase is not important in pathogenicity on tomato plants. However, conservation of tomA on a pathogenicity island in S. acidiscabies and S. turgidiscabies suggests a role in plant-microbe interaction.

Hydroxycinnamic Acid Degradation, a Broadly Conserved Trait, ProtectsRalstonia solanacearumfrom Chemical Plant Defenses and Contributes to Root Colonization and Virulence

“…Pseudomonas syringae uses type III effectors to manipulate plant phenylpropanoids (Truman et al, 2006). Many plant pathogens protect themselves with drug efflux pumps, while others enzymatically degrade the plant defense compounds pisatin, tomatine, and HCAs (Tegtmeier and VanEtten, 1982; Tegos et al, 2002; Brown et al, 2007; Seipke and Loria, 2008; Michielse et al, 2012). Our results support a general model that root-infecting pathogens encounter toxic concentrations of HCAs, and that degradation of these defenses is important for pathogenic success.…”

Genome Content and Phylogenomics Reveal both Ancestral and Lateral Evolutionary Pathways in Plant-Pathogenic Streptomyces Species

“…turgidiscabies Car8 contains two copies of the tomA cluster. Previous studies determined that S. turgidiscabies encodes the ␣-tomatine-detoxifying enzyme TomA and that tomA is linked to a cluster of glycoside hydrolases (tomA cluster) (41). This tomA cluster is located within the mobile genomic island PAISt, and it has homologs within nonmobile yet syntenic PAIs in S. scabies and S. acidiscabies (2,14).…”

The complex extracellular biology ofStreptomyces

“…Virulence is mainly dependent on their inhibition of plant cellulose synthesis, by the production of thaxtomins, 4‐nitroindol‐3‐yl‐containing 2,5‐dioxopiperazines (Bischoff et al , 2009; King & Calhoun, 2009). In Streptomyces turgidiscabies , the DNA encoding thaxtomin biosynthesis is in a large pathogenicity island that also includes genes for necrosis ( nec1 ) and a tomatinase ( tomA ) (Joshi et al , 2007; Loria et al , 2008; Seipke & Loria, 2008), and for production of nitric oxide, a key regulatory molecule for several plant processes (Johnson et al , 2008). However, some pathogenic isolates lack either nec1 or tomA or both (Lerat et al , 2009).…”