A 51 kDa protein kinase of potato activated with hyphal wall components from Phytophthora infestans

In potato tuber tissue, treatment of fungal elicitor, hyphal wall components (HWC) induces various plant defense reactions. As treatment of protein kinase inhibitor prior to HWC treatment blocks some of defense reactions induced by HWC, involvement of protein kinases in plant defense induction is proposed. Here, we demonstrate HWC-induced activation of a 51-kDa protein kinase (abbreviated p51-PK) using myelin basic protein as a substrate in potato tuber discs. The activity of pS1-PK was not detected in the absence of phosphatase inhibitor, NaF, and p51-PK was immunoprecipitated with antibody against phosphotyrosine. Pretreatment of phospholipase C inhibitor, neomycin, and GTP-binding protein activator, mastoparan, partially inhibited the HWC-induced activation of p51-PK, suggesting possible involvement of phospholipase C and GTP-binding protein in the activation of p51-PK. Exogenously supplied elicitors, salicylic acid and arachidonic acid, which are known to induce various defense responses in potato plants, also activated the protein kinase showing the same migration as p51-PK on SDS-PAGE and different activation patterns. These results implied that p51-PK might be involved in several signal transduction pathways leading to plant defense responses initiated by different stimuli.