A novel species-level group of streptomyces exhibits variation in phytopathogenicity despite conservation of virulence loci

Authors: WEISBERG, ALEXANDRA - Oregon State University; KOTHA, RAGHAVENDHAR - University Of Maryland; KRAMER, CHARLES - University Of Maryland; CHANG, JEFF - Oregon State University; Luthria, Devanand - Dave; Clarke, Christopher

Submitted to: Molecular Plant-Microbe Interactions
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 10/6/2020
Publication Date: 12/3/2020
Citation: Weisberg, A., Kotha, R., Kramer, C., Chang, J., Luthria, D.L., Clarke, C.R. 2020. Whole-genome sequencing of five Streptomyces isolates identifies a new pathogenic species group that causes common scab disease of potato. Molecular Plant-Microbe Interactions. 34(1):39-48. https://doi.org/10.1094/MPMI-06-20-0164-R.
DOI: https://doi.org/10.1094/MPMI-06-20-0164-R

Interpretive Summary: Common scab disease of potato occurs in all potato-growing regions of the world with severe economic impact. In the United States, common scab is caused by at least six species of Streptomyces bacteria. The Genetic Improvement for Fruits and Vegetables Lab maintains a collection of more than 3000 Streptomyces isolates, including pathogenic isolates from 24 states and five Canadian provinces. We analyzed five pathogenic Streptomyces isolates from two states that are part of a novel species group by whole genome sequencing and quantifying potato pathogenicity. Surprisingly, there was remarkable diversity in pathogenicity among these five strains despite a high degree of genetic similarity. This result indicates that sub-species level characterization of Streptomyces strains is necessary for accurate prediction of potential pathogenicity. These results will benefit researches in devising effective strategies to control this destructive potato pathogen.

Technical Abstract: The genus Streptomyces includes several pathogenic species that cause common scab disease on potato and other tuber and root crops. Elicitation of common scab symptoms is primarily due to the effects of the Streptomyces-produced toxin thaxtomin A. Over ten species of Streptomyces synthesize thaxtomin A and all are pathogens of potato. We phenotyped and sequenced the whole genomes of five strains of Streptomyces that contain the thaxtomin A biosynthetic genes and are members of a novel species. Only three of these strains are aggressive plant pathogens and only four of the strains produce the thaxtomin A toxin in toxin-inducing liquid media. Multiple deletions are present in and around the thaxtomin biosynthetic gene cluster of the characterized low pathogenicity strains. Therefore, presence of the thaxtomin A biosynthetic genes and production of thaxtomin A may be necessary for common scab but are not sufficient.