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

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


Helen Neale
Occasional Associate Lecturer - HAS DAS

Robert Jackson

Gail Preston

Dawn Arnold


© 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.


Neale, H., Jackson, R., Preston, G., & Arnold, D. (2018). Supercoiling of an excised genomic island represses effector gene expression to prevent activation of host resistance. Molecular Microbiology, 110(3), 444-454.

Journal Article Type Article
Acceptance Date Aug 22, 2018
Online Publication Date Aug 28, 2018
Publication Date Nov 1, 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
Keywords genes
Public URL
Publisher URL


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