Melisa T. S.
Department of Biology, Washington University, St Louis, MO 63130, U.S.A.
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Accepted 7 March 2005.
In order to cause disease on plants, gram-negative phytopathogenic bacteria introduce numerous virulence factors into the host cell in order to render host tissue more hospitable for pathogen proliferation. The mode of action of such bacterial virulence factors and their interaction with host defense pathways remain poorly understood. avrRpt2, a gene from Pseudomonas syringae pv. tomato JL1065, has been shown to promote the virulence of heterologous P. syringae strains on Arabidopsis thaliana. However, the contribution of avrRpt2 to the virulence of JL1065 has not been examined previously. We show that a mutant derivative of JL1065 that carries a disruption in avrRpt2 is impaired in its ability to cause disease on tomato (Lycopersicon esculentum), indicating that avrRpt2 also acts as a virulence gene in its native strain on a natural host. The virulence activity of avrRpt2 was detectable on tomato lines that are defective in either ethylene perception or the accumulation of salicylic acid, but could not be detected on a tomato mutant insensitive to jasmonic acid. The enhanced virulence conferred by the expression of avrRpt2 in JL1065 was not associated with the suppression of several defense-related genes induced during the infection of tomato.
type III secretion
© 2005 The American Phytopathological Society