抄録
Ca^<2+> signals have evolved a wide spectrum of strategies as intra/intercellular signals. Even though Ca^<2+>-binding sensory proteins like Ca^<2+>-dependent protein kinase (CDPK) are expected to act as intracellular protein mediators that govern gene regulation networks in response to Ca^<2+> influx after herbivory, little is known about the mechanisms. To investigate whether CDPKs play certain roles in an herbivore response-signaling pathway, we screened the characteristics of Arabidopsis CDPK mutants damaged by a feeding generalist herbivore, Spodoptera littoralis. After herbivory, the cpk3 and cpk13 mutants showed lower transcript levels of plant defensin gene PDF1.2 compared to wild-type plants. These CDPKs appear to be located mainly in the nucleus/cytosol, and in vitro kinase assays of the CDPK proteins with 87 defense-related transcription factors (TFs), synthesized from the wheat germ cell-free system, demonstrated that CPK3 phosphorylates TFs and ATL2 (a member of the RING-H2 zinc finger proteins that may function as E3 ubiquitin ligase) as substrate targets. Rather, while CPK13 does not phosphorylate any of them, this kinase is predicted to be involved in the green leaf volatile-signaling pathway. The results presented show that CPK3 and CPK13 are involved in controlling the herbivore-induced expression of plant defensin gene, and that they exert such control through distinct mechanisms by directly interacting with transcription factors or volatile-mediated gene regulation.
