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Plasticity in Plant-Growth-Promoting and Phytopathogenic Bacteria
2014; Page: 99 - 129

Genome Plasticity and Dynamic Evolution of Phytopathogenic Pseudomonads and Related Bacteria

Marco Scortichini, Simone Marcelletti, Patrizia Ferrante, Milena Petriccione, Emanuela Torelli, Giuseppe Firrao

C.R.A., Consiglio per la Ricerca e Sperimentazione in Agricultura, Centro di Ricerca per la Frutticoltura, 52 Via di Fioranello, Rome, 00134, Italy.

Abstract

Pseudomonads represent widely distributed plant pathogenic bacteria, which cause diseases in most cultivated mono and dicotyledonous crops worldwide. Currently, 25 phytopathogenic Pseudomonas spp. have been identified and described; four of these species contain distinct pathovars. The general features of Pseudomonas syringae and Pseudomonas savastanoi include a genome size of approximately 6 Mb, with a 57–59 % G + C content, 5,200–5,700 protein-encoding genes, and 85.6–88.7 % coding sequences. The core genome of the P. syringae species complex contains 3,397 genes, whereas its “pan” genome, currently based on the genomic assessment of 19 different pathovars, contains 12,749 genes. Many strains of P. syringae pathovars contain one or more plasmids with an extensive amount of shared DNA sequences. There are striking examples of how the acquisition or loss of an entire plasmid or genomic (pathogenicity) island harboured from a particular plasmid determines a differential response of the host plant to bacterial attack. Cases of evolution through the gain or loss of a whole plasmid or its part are illustrated. Examples of dynamic genetic rearrangements involving genes for elicitors of the plant immunity system, the type III secretion system, and their effector proteins are illustrated along with a case of pathogen convergent evolution to the same host plant and the evolutionary dynamics found in Ralstonia solanacearum. Finally, cell-to-cell communication and two-component signal transduction are discussed in the global network of regulated communication.

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