CALCIUM-DEPENDENT PROTEIN-KINASE GENES IN CORN ROOTS

Two cDNAs encoding Ca2+-dependent protein kinases (CDPKs), CRPK1 and C RPK2 (corn root protein kinase 1 and 2), were isolated from the root t ip library of corn (Zea mays L., cv. Merit) and their nucleotide seque nces were determined. Deduced amino acid sequences of both the clones have features characteristic of plant CDPKs, including all 11 conserve d serine/threonine kinase subdomains, a junction domain and a calmodul in-like domain with four Ca2+-binding sites. Northern analysis reveale d that CRPK1 mRNA is preferentially expressed in roots, especially in the root tip; whereas, the expression of CRPK2 mRNA was very low in al l the tissues tested. In situ hybridization experiments revealed that CRPK1 mRNA is highly expressed in the root apex, as compared to other parts of the root; Partially purified CDPK from the root tip phosphory lates syntide-2, a common peptide substrate for plant CDPKs, and the p hosphorylation was stimulated 7-fold by the addition of Ca2+. Our resu lts show that two CDPK isoforms are expressed in corn roots and they m ay be involved in the Ca2+-dependent signal transduction process.