A Wound-Responsive and Phospholipid-Regulated Maize Calcium-Dependent Protein Kinase

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Abstract
Using protein sequence data obtained from a calcium- and phospholipid-regulated protein kinase purified from maize (Zea mays), we isolated a cDNA encoding a calcium-dependent protein kinase (CDPK), which we designated ZmCPK11. The deduced amino acid sequence of ZmCPK11 includes the sequences of all the peptides obtained from the native protein. The ZmCPK11 sequence contains the kinase, autoregulatory, and calmodulin-like domains typical of CDPKs. Transcripts for ZmCPK11 were present in every tested organ of the plant, relatively high in seeds and seedlings and lower in stems, roots, and leaves. In leaves, kinase activity and ZmCPK11 mRNA accumulation were stimulated by wounding. The level of ZmCPK11 is also increased in noninjured neighboring leaves. The results suggest that the maize protein kinase is involved in a systemic response to wounding. Bacterially expressed glutathione S-transferase (GST)-ZmCPK11 was catalytically active in a calcium-dependent manner. Like the native enzyme, GST-ZmCPK11 was able to phosphorylate histone III-S and Syntide 2. Phosphorylation of histone was stimulated by phosphatidylserine, phosphatidylinositol, and phosphatidic acid, whereas phosphatidylcholine, lysophosphatidylcholine, phosphatidylethanolamine, diolein, and cardiolipin did not increase the enzymatic activity. Autophosphorylation of GST-ZmCPK11 was stimulated by calcium and by phosphatidic acid and, to a lesser extent, by phosphatidylserine. Phosphatidylcholine did not affect autophosphorylation. These data unequivocally identify the maize phospholipid- and calcium-regulated protein kinase, which has protein kinase C-like activity, as a CDPK, and emphasize the potential that other CDPKs are regulated by phospholipids in addition to calcium.

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