Supercoiling of an excised genomic island represses effector gene expression to prevent activation of host resistance

Neale, Helen; Jackson, Robert; Preston, Gail; Arnold, Dawn

Abstract

© 2018 The Authors Molecular Microbiology Published by John Wiley & Sons Ltd. The plant pathogen Pseudomonas syringae pv. phaseolicola, which causes halo blight disease of beans, contains a 106kb genomic island PPHGI-1. PPHGI-1 carries a gene, avrPphB, which encodes an effector protein that triggers a resistance response in certain bean cultivars. Previous studies have shown that when PPHGI-1 is excised from the bacterial chromosome, avrPphB is downregulated and therefore the pathogen avoids triggering the host’s defence mechanism. Here, we investigate whether the downregulation of avrPphB is caused by the supercoiling of PPHGI-1. We also investigate the effect of a PPHGI-1-encoded type 1A topoisomerase, TopB3, on island stability and bacterial pathogenicity in the plant. Supercoiling inhibitors significantly increased the expression of avrPphB but did not affect the excision of PPHGI-1. An insertional mutant of topB3 displayed an increase in avrPphB expression and an increase in PPHGI-1 excision as well as reduced population growth in resistant and susceptible cultivars of bean. These results suggest an important role for topoisomerases in the maintenance and stability of a bacterial-encoded genomic island and demonstrate that supercoiling is involved in the downregulation of an effector gene once the island has been excised, allowing the pathogen to prevent further activation of the host defence response.

• Journal Article Type: Article
• Acceptance Date: Aug 22, 2018
• Online Publication Date: Aug 28, 2018
• Publication Date: Nov 1, 2018
• Deposit Date: Sep 24, 2018
• Publicly Available Date: Oct 10, 2018
• Journal: Molecular Microbiology
• Print ISSN: 0950-382X
• Electronic ISSN: 1365-2958
• Publisher: Wiley
• Peer Reviewed: Peer Reviewed
• Volume: 110
• Issue: 3
• Pages: 444-454
• DOI: https://doi.org/10.1111/mmi.14111
• Keywords: genes
• Public URL: https://uwe-repository.worktribe.com/output/862698
• Publisher URL: https://doi.org/10.1111/mmi.14111
• Contract Date: Sep 24, 2018