Arabidopsis thaliana EDS4 contributes to salicylic acid (SA)-dependent expression of defense responses: Evidence for inhibition of jasmonic acid signaling by SA

The Arabidopsis enhanced disease susceptibility 4 (eds4) mutation causes en hanced susceptibility to infection by the bacterial pathogen Pseudomonas sy ringae pv, maculicola ES4326 (Psm ES4326). Gene-for-gene resistance to bact eria carrying the avirulence gene avrRpt2 is not significantly affected by eds4, Plants homozygous for eds4 exhibit reduced expression of the pathogen esis-related gene PR-I 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 rol e 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), T wo mutations that cause reduced SA levels, eds4 and pad4, cause heightened responses to inducers of JA-dependent gene expression, providing genetic ev idence 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.