Calcium and secondary CPK signaling in plants in response to herbivore attack

Plant Ca(2+) signals are involved in a sizable array of intracellular signaling pathways after pest invasion. Upon herbivore feeding there is a dramatic Ca(2+) influx, followed by the activation of Ca(2+)-dependent signal transduction pathways that include interacting downstream networks of kinases for defense responses. Notably, Ca(2+)-binding sensory proteins such as Ca(2+)-dependent protein kinases (CPKs) have recently been documented to mediate the signaling following Ca(2+) influx after herbivory, in phytohormone-independent manners. Here, we review the sequence of signal transductions triggered by herbivory-evoked Ca(2+) signaling leading to CPK actions for defense responses, and discuss in a comparative way the involvement of CPKs in the signal transduction of a variety of other biotic and abiotic stresses.