1Molecular and Cell Biology Graduate Program, University of Maryland, College Park 20742, U.S.A.; 2Novartis Agribusiness Biotechnology Research, Inc., P.O. Box 12257, 3054 Cornwallis Road, Research Triangle Park, NC 27709-2257, U.S.A.; 3Novartis Agricultural Discovery Institute, Inc., 3115 Merryfield Row Ste.100, San Diego, CA 92121, U.S.A.
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Accepted 7 January 2000.
The Arabidopsis enhanced disease susceptibility 4 (eds4) mutation causes enhanced susceptibility to infection by the bacterial pathogen Pseudomonas syringae pv. Maculicola ES4326 (Psm ES4326). Gene-for-gene resistance to bacteria carrying the avirulence gene avrRpt2 is not significantly affected by eds4. Plants homozygous for eds4 exhibit reduced expression of the pathogenesis-related gene PR-1 after infection by Psm ES4326, weakened responses to treatment with the signal molecule salicylic acid (SA), impairment of the systemic acquired resistance response, and reduced accumulation of SA after infection with Psm ES4326. These phenotypes indicate that EDS4 plays a role in SA-dependent signaling. SA has been shown to have a negative effect on activation of gene expression by the signal molecule jasmonic acid (JA). Two mutations that cause reduced SA levels, eds4 and pad4, cause heightened responses to inducers of JA-dependent gene expression, providing genetic evidence to support the idea that SA interferes with JA-dependent signaling. Two possible working models of the role of EDS4 in governing activation of defense responses are presented.
© 2000 The American Phytopathological Society