Abstract
Calcium-dependent protein kinases (CPKs) have been predicted to mediate the signaling following Ca2+ influx after insect herbivory. To investigate the roles CPKs play in a herbivore response-signaling pathway, we screened the characteristics of Arabidopsis CPK mutants damaged by Spodoptera littoralis. Following insect attack, the cpk3 and cpk13 mutants showed lower transcript levels of plant defensin gene PDF1.2 compared to wild-type plants. In vitro kinase assays of the CPK proteins with a suite of substrates demonstrated that the protein phosphorylates transcription factors (including HsfB2a). In vivo agroinflitaration assays showed that CPK-derived phosphorylation of HsfB2a promotes PDF1.2 transcriptional activation in defense response. Furthermore, both CPKs are involved in the transcript level of heat shock protein (HSP) genes, which resulted in impairment of basal thermotolerance in cpk3 and cpk13 mutants. However, HsfB2a played a role in HSP transcripts as suppressor. These results reveal an intricate array of CPK-associated signal transduction networks that are in part common, but by distinct mechanisms, between plant-insect interactions and heat-shock signal transduction.
