Signals regulating multiple responses to wounding and herbivores

Damage inflicted by herbivore feeding necessitates multiple defense strateg ies in plants. The wound site must be sealed and defense responses mounted against the herbivore itself and against invading opportunistic pathogens. These defenses are controlled both in time and space by highly complex regu latory networks that themselves are modulated by interactions with other si gnaling pathways. In this review, we describe the signaling events that occ ur in individual wounded leaves, in systemic unwounded regions of the plant , and between the plant,and other organisms, and attempt to place these eve nts in the context of a coordinated system. Key signals that are discussed include ion fluxes, active oxygen species, protein phosphorylation cascades , the plant hormones jasmonic acid, ethylene, abscisic acid and salicylic a cid, peptide signals, glycans, volatile chemicals, and physical signals suc h as hydraulic and electrical signals. Themes that emerge after considerati on of the published data are that glycans and peptide elicitors are likely primary triggers of wound-induced defense responses and that they function through the action of jasmonic acid, a central mediator of defense gene exp ression, whose effect is modulated by ethylene, In the field, wound signali ng pathways are significantly impacted on by other stress response pathways , including pathogen responses that often operate through potentially antag onistic signals such as salicylic acid. However, gross generalisations are not possible because some wound and pathogen responses operate through comm on jasmonate- and ethylene-dependent pathways. Understanding the ways in wh ich local and systemic wound signaling pathways are coordinated individuall y and in the context of the plants wider environment is a key challenge in the application of this science to crop-protection strategies.