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Confocal Imaging of Pseudomonas syringae pv. phaseolicola Colony Development in Bean Reveals Reduced Multiplication of Strains Containing the Genomic Island PPHGI-1

October 2010 , Volume 23 , Number  10
Pages  1,294 - 1,302

S. A. C. Godfrey,1 J. W. Mansfield,2 D. S. Corry,1 H. C. Lovell,1 R. W. Jackson,3 and D. L. Arnold1

1Centre for Research in Plant Science, The University of the West of England, Bristol, BS16 1QY, U.K.; 2Division of Biology, Imperial College London, London, SW7 2AZ, U.K.; 3School of Biological Sciences, University of Reading, RG6 6AJ, U.K.

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Accepted 27 June 2010.

Pseudomonas syringae pv. phaseolicola is the seed borne causative agent of halo blight in the common bean Phaseolus vulgaris. Pseudomonas syringae pv. phaseolicola race 4 strain 1302A contains the avirulence gene hopAR1 (located on a 106-kb genomic island, PPHGI-1, and earlier named avrPphB), which matches resistance gene R3 in P. vulgaris cultivar Tendergreen (TG) and causes a rapid hypersensitive reaction (HR). Here, we have fluorescently labeled selected Pseudomonas syringae pv. phaseolicola 1302A and 1448A strains (with and without PPHGI-1) to enable confocal imaging of in-planta colony formation within the apoplast of resistant (TG) and susceptible (Canadian Wonder [CW]) P. vulgaris leaves. Temporal quantification of fluorescent Pseudomonas syringae pv. phaseolicola colony development correlated with in-planta bacterial multiplication (measured as CFU/ml) and is, therefore, an effective means of monitoring Pseudomonas syringae pv. phaseolicola endophytic colonization and survival in P. vulgaris. We present advances in the application of confocal microscopy for in-planta visualization of Pseudomonas syringae pv. phaseolicola colony development in the leaf mesophyll to show how the HR defense response greatly affects colony morphology and bacterial survival. Unexpectedly, the presence of PPHGI-1 was found to cause a reduction of colony development in susceptible P. vulgaris CW leaf tissue. We discuss the evolutionary consequences that the acquisition and retention of PPHGI-1 brings to Pseudomonas syringae pv. phaseolicola in planta.

© 2010 The American Phytopathological Society