Interacting signal pathways control defense gene expression in Arabidopsisin response to cell wall-degrading enzymes from Erwinia carotovora

We have characterized the role of salicylic acid (SA)independent defense si gnaling in Arabidopsis thaliana in response to the plant pathogen Erwinia c arotovora subsp, carotovora, Use of pathway-specific target genes as well a s signal mutants allowed us to elucidate the role and interactions of ethyl ene, jasmonic acid (JA), and SA signal pathways in this response. Gene expr ession studies suggest a central role for both ethylene and JA pathways in the regulation of defense gene expression triggered by the pathogen or by p lant cell wall-degrading enzymes (CF) secreted by the pathogen. Our results suggest that ethylene and JA act in concert in this regulation. In additio n, CF triggers another, strictly JA-mediated response inhibited by ethylene and SA. SA does not appear to have a major role in activating defense gene expression in response to CE However, SA may have a dual role in controlli ng CF-induced gene expression, by enhancing the expression of genes synergi stically induced by ethylene and JA and repressing genes induced by JA alon e.