MOLECULAR-CLONING AND BIOCHEMICAL-CHARACTERIZATION OF A RECEPTOR-LIKE SERINE/THREONINE KINASE FROM RICE

A receptor-like protein kinase, OsPK10, has been cloned from rice (Oryza sativa). The 2.8 kb cDNA contains an open reading frame capable of encoding a peptide sequence of 824 amino acids. The topological features of the predicted OsPK10 protein include an N-terminal signal peptide, a cysteine-rich extracellular ligand-binding domain, a membrane-spanning segment, and a cytoplasmic domain possessing all the hallmarks of catalytic domains of eukaryotic protein kinases. The cytoplasmic domain was selectively expressed in Escherichia coli and assayed for kinase activity. The results show the protein is capable of autophosphorylation using either ATP or GTP as the phosphate donor. Phosphoamino acid analysis reveals phosphorylation of threonines, consistent with the substrate specificity indicated by sequence motifs in the catalytic core. A single amino acid substitution of Glu for Lys-528 completely abolishes autophosphorylation activity. DNA gel blot analyses suggest that the haploid rice genome contains a single copy of the OsPK10 gene. OsPK10 transcripts appear to be more abundant in shoots than in roots of rice seedlings.