Professor Memorial University of Newfoundland St. John's, Newfoundland and Labrador, Canada
The soil dwelling bacterium Streptomyces scabiei is distributed worldwide and is the causative agent of the economically important crop disease potato common scab (CS). The cellulose biosynthesis inhibitor thaxtomin A (ThxA) is the principal pathogenicity factor produced by S. scabiei and is essential for CS development. In addition, S. scabiei synthesizes the virulence-associated phytotoxin N-coronafacoyl-L-isoleucine (CFA-Ile), which is predicted to function as a jasmonic acid hormone mimic, and it produces the concanamycin phytotoxins, which function as inhibitors of vacuolar-type ATPases. Previous research suggests that concanamycin production may impact the virulence of S. scabiei, though their exact role in host-pathogen interactions has not been established. The goal of this study was to examine the contribution of the concanamycins to the virulence of S. scabiei, alone and in conjunction with ThxA and CFA-Ile. S. scabiei mutants that are altered in the production of concanamycins, ThxA, and/or CFA-Ile were constructed and used in plant bioassays to assess the virulence phenotype of each compared to wild-type S. scabiei. In addition, confocal laser scanning microscopy was used along with green fluorescent protein-labeled mutant strains to investigate the contribution of the concanamycins and other phytotoxins to plant tissue colonization. The results of this study provide new insights into the molecular mechanisms of CS disease and S. scabiei-host interactions.
