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

Abstract

Plants possess inducible defense mechanisms to protect themselves against attack by microbial pathogens and herbivorous insects. The endogenous signaling 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 nonprotein 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. Recent advances in induced resistance research revealed that the signaling pathways involved are interconnected, resulting in overlap, synergism, and antagonism between the different signal transduction pathways. Divergence and crosstalk of pathways in defense response signaling provide the plant with flexibility and the opportunity for fine-tuning of resistance responses, thereby enabling it to cope with different forms of stress more efficiently.