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The stealth episome: Suppression of gene expression on the excised genomic island PPHGI-1 from Pseudomonas syringae pv. phaseolicola

Godfrey, Scott A.C.; Lovell, Helen C.; Corry, David; Mansfield, John W.; Jackson, Robert W.; Arnold, Dawn L.

Authors

Scott A.C. Godfrey

Helen C. Lovell

David Corry

John W. Mansfield

Robert W. Jackson

Dawn Arnold Dawn.Arnold@uwe.ac.uk
Professor in Molecular Plant Pathology



Abstract

Pseudomonas syringae pv. phaseolicola is the causative agent of halo blight in the common bean, Phaseolus vulgaris. P. syringae pv. phaseolicola race 4 strain 1302A contains the avirulence gene avrPphB (syn. hopAR1), which resides on PPHGI-1, a 106 kb genomic island. Loss of PPHGI-1 from P. syringae pv. phaseolicola 1302A following exposure to the hypersensitive resistance response (HR) leads to the evolution of strains with altered virulence. Here we have used fluorescent protein reporter systems to gain insight into the mobility of PPHGI-1. Confocal imaging of dual-labelled P. syringae pv. phaseolicola 1302A strain, F532 (dsRFP in chromosome and eGFP in PPHGI-1), revealed loss of PPHGI-1::eGFP encoded fluorescence during plant infection and when grown in vitro on extracted leaf apoplastic fluids. Fluorescence-activated cell sorting (FACS) of fluorescent and non-fluorescent PPHGI-1::eGFP F532 populations showed that cells lost fluorescence not only when the GI was deleted, but also when it had excised and was present as a circular episome. In addition to reduced expression of eGFP, quantitative PCR on sub-populations separated by FACS showed that transcription of other genes on PPHGI-1 (avrPphB and xerC) was also greatly reduced in F532 cells harbouring the excised PPHGI-1::eGFP episome. Our results show how virulence determinants located on mobile pathogenicity islands may be hidden from detection by host surveillance systems through the suppression of gene expression in the episomal state. © 2011 Godfrey et al.

Citation

Lovell, H. C., Godfrey, S. A., Mansfield, J. W., Corry, D., Jackson, R. W., & Arnold, D. L. (2011). The stealth episome: Suppression of gene expression on the excised genomic island PPHGI-1 from Pseudomonas syringae pv. phaseolicola. PLoS Pathogens, 7(3), https://doi.org/10.1371/journal.ppat.1002010

Journal Article Type Article
Publication Date Mar 1, 2011
Journal PLoS Pathogens
Print ISSN 1553-7366
Electronic ISSN 1553-7374
Publisher Public Library of Science
Peer Reviewed Peer Reviewed
Volume 7
Issue 3
DOI https://doi.org/10.1371/journal.ppat.1002010
Keywords stealth, episome, suppression of gene expression, excised genomic island, PPHGI-1, Pseudomonas syringae pv. phaseolicola
Public URL https://uwe-repository.worktribe.com/output/964761
Publisher URL http://dx.doi.org/10.1371/journal.ppat.1002010