Signal interactions in induced resistance to pathogens and insect herbivores

Plants are often simultaneously challenged by pathogens and insects capable of triggering an array of responses that may be beneficial or detrimental to the plant. The efficacy of resistance mechanisms can be strongly influen ced by the mix of signals generated by biotic stress as well as abiotic str ess such as drought, nutrient limitation or high soil salinity. An understa nding of their biochemical nature, and knowledge of the specificity and com patibility of the signaling systems that regulate the expression of inducib le responses could optimize the utilization of these responses in crop prot ection. Signaling conflicts and synergies occur during a plant's response t o pathogens and insect herbivores, and much of the research on defense sign aling has focused on salicylate- and jasmonate-mediated responses. We will review our results using tomato (Lycopersicon esculentum) in greenhouse and field studies that illustrate a trade-off between salicylate- and jasmonat e-mediated signaling, and discuss research on strategies to minimize the tr ade-off that can occur following the application of chemical elicitors of r esistance. In addition, there is evidence of another signaling system that mediates endogenous levels of ceramide in the plant. This signal is associa ted with programmed cell death and protection of tomato against the fungal pathogen Alternaria alternata f. sp. lycopersici.