# Concanamycins Are Key Contributors to the Virulence of the Potato Common Scab Pathogen Streptomyces scabiei

## TL;DR

This study shows that concanamycins, produced by the bacterium Streptomyces scabiei, increase its ability to cause potato common scab disease.

## Contribution

The study provides direct evidence that concanamycins enhance the virulence of Streptomyces scabiei.

## Key findings

- Concanamycins increase disease severity on radish seedlings and potato tuber tissue.
- Concanamycin production is regulated by two genes within its biosynthetic gene cluster.
- Concanamycin biosynthesis and thaxtomin A production are modulated by different nutritional signals.

## Abstract

The soil‐dwelling bacterium
Streptomyces scabiei
is distributed worldwide and is the best‐characterised causative agent of common scab disease, which impacts potato crops and causes significant economic losses to growers. The principal pathogenicity factor responsible for common scab development is the phytotoxin thaxtomin A, which functions as a cellulose biosynthesis inhibitor in plants.
S. scabiei
also produces polyketide compounds belonging to the concanamycin family, which serve as inhibitors of eukaryotic vacuolar‐type ATPases and have been shown to exhibit phytotoxic activity against different plant species. It has been proposed that concanamycins contribute to the virulence of
S. scabiei, but direct evidence of this has been lacking. Using constructed strains of
S. scabiei
that are either unable to produce concanamycins or produce elevated levels of the metabolites, we showed that concanamycins enhance the severity of disease symptoms induced by
S. scabiei
on radish seedlings and potato tuber tissue. We demonstrated that concanamycin production is controlled by two regulatory genes that are situated within the concanamycin biosynthetic gene cluster, and that production of concanamycins and thaxtomin A by
S. scabiei
is modulated by different nutritional signals. The concanamycin biosynthetic gene cluster is conserved in other common scab‐causing Streptomyces spp., suggesting that these metabolites may function as important virulence determinants in multiple phytopathogenic species. Overall, this study expands our understanding of the molecular factors that enable plant host colonisation and common scab disease development by
S. scabiei.

Production of concanamycins by the potato common scab pathogen
Streptomyces scabiei
is associated with an enhanced virulence phenotype and is controlled by genetic and environmental factors. Created using BioRender.