Cytokinin Signal Transduction

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(1) A gene encoding a protein kinase was isolaed from wheat seedings, and designated as wpk4.(2) The WPK4 protein was expressed in E.coli and Bacullo virus system.(3) The enzymatic activity was evaluated using expressed proteins, and shown to possess autophosphorylation activity and MBP kinase activity in the presence of manganese ions.(4) A specific antibody was raised against expressed WPK4.(5) The enzyme specifically phosphorylated 65 kDa and 17.6 kDa proteins extracted from wheat seedings.(6) Under poor nutrient conditions, transcripts of wpk4 greatly accumulated in seedlings.(7) Upon transferring seedlings grown under nutrient-poor media into nutrient rich-media, transcripts of wpk4 rapidly disappeared.(8) Cytokinin treatment of seedlings induced accumulation of transcripts of wpk4.(9) The results suggest that WPK4 is a member of the nutrient signal transduction system, and that cytokinin functions in it as an activator of the system.