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

Neale, H. C., Jackson, R. W., Preston, G. M. and Arnold, D. L. (2018) Supercoiling of an excised genomic island represses effector gene expression to prevent activation of host resistance. Molecular Microbiology, 110 (3). pp. 444-454. ISSN 0950382X doi: 10.1111/mmi.14111

Abstract/Summary

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 down regulated and therefore the pathogen avoids triggering the host’s defence mechanism. Here we investigate whether the down regulation of avrPphB is caused by supercoiling of PPHGI-1. We also investigate the effect of a PPHGI-1 encoded type 1A topoisomerase, TopB3, on island stability and the 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 down regulation of an effector gene once the island has been excised, allowing the pathogen to prevent further activation of the host defence response.

Item Type	Article
URI	https://reading-clone.eprints-hosting.org/id/eprint/78888
Identification Number/DOI	10.1111/mmi.14111
Refereed	Yes
Divisions	Life Sciences > School of Biological Sciences > Biomedical Sciences Life Sciences > School of Biological Sciences > Ecology and Evolutionary Biology
Publisher	Wiley
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