Role of early signaling events in plant-insect interactions

The response of plants to the stress caused by herbivores involves several different defense mechanisms. These responses begin at the plant cell plasma membrane, where insect herbivores interact physically by causing mechanical damage and chemically by introducing elicitors or triggering plant-derived signaling molecules. The earliest plant responses to herbivore contact are represented by ion flux unbalances generated in the plant cell plasma membrane at the damaged site. Differences in the charge distribution generate plasma transmembrane potential (Vm) variation, the first event that eventually leads to the initiation of signal transduction pathways and gene expression. Calcium signaling and the generation of reactive oxygen and nitrogen species are early events closely related to Vm variations. This review provides an update on recent developments and advances in plant early signaling in response to herbivory, with particular emphasis on the electrophysiological variations of the plasma membrane potential, calcium signaling, cation channel activity, the production of reactive oxygen and nitrogen species, and the formation of a systemically moving signal from wounded tissues. The roles of calcium dependent protein kinases and calcineurin signaling are also discussed.