Open AccessEvidence That Thaxtomin C Is a Pathogenicity Determinant of Streptomyces ipomoeae, the Causative Agent of Streptomyces Soil Rot Disease of Sweet Potato
Author(s) -
Dongli Guan,
Brenda L. Grau,
Christopher A. Clark,
Carol M. Taylor,
Rosemary Loria,
Gregg S. Pettis
Publication year - 2012
Publication title -
molecular plant-microbe interactions
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.565
H-Index - 153
eISSN - 1943-7706
pISSN - 0894-0282
DOI - 10.1094/mpmi-03-11-0073
Subject(s) - phytotoxin , streptomyces , common scab , biology , mutant , pathogen , microbiology and biotechnology , context (archaeology) , botany , gene , bacteria , genetics , toxin , paleontology
Streptomyces ipomoeae is the causal agent of Streptomyces soil rot of sweet potato, a disease marked by highly necrotic destruction of adventitious roots, including the development of necrotic lesions on the fleshy storage roots. Streptomyces potato scab pathogens produce a phytotoxin (thaxtomin A) that appears to facilitate their entrance into host plants. S. ipomoeae produces a less-modified thaxtomin derivative (thaxtomin C) whose role in pathogenicity has not been examined. Here, we cloned and sequenced the thaxtomin gene cluster (txt) of S. ipomoeae, and we then constructed targeted txt mutants that no longer produced thaxtomin C. The mutants were unable to penetrate intact adventitious roots but still caused necrosis on storage-root tissue. These results, taken in context with previous histopathological study of S. ipomoeae infection, suggest that thaxtomin C plays an essential role in inter- and intracellular penetration of adventitious sweet potato roots by S. ipomoeae. Once inside the plant host, the pathogen uses one or more yet-to-be-determined factors to necrotize root tissue, including that of any storage roots it encounters.