Signaling in plant resistance responses: divergence and cross-talk of defense pathways

Plants possess inducible defense mechanisms to protect themselves against attack by microbial pathogens and herbivorous insects. The endogenous signalling molecules salicylic acid, ethylene, and jasmonic acid, and the peptide messenger systemin play important roles in the regulation of these induced defense responses. Disease resistance of plants can also be induced by chemical agents, such as 2.6 dichloroisonicotinic acid, benzothiadiazole and the non-protein amino acid β-aminobutyric acid. In most cases, these chemical agents mimic or ingeniously make use of the same pathways that are activated by the endogenous defense signals. This review is focussed on the current state of research on signal transduction pathways involved in induced resistance against pathogens and insects