Molecular Characterization Of OsBIWNK1, A Rice WNK Protein Kinase Gene

Protein kinases play important roles in plant growth and development, hormone response as well as in response to abiotic and biotic stress. Previously, we have found that two rice mitogen-activated protein kinases are involved in rice disease resistance responses, to further study putative protein kinses in disease resistance response, we cloned and characterized a noval rice serine/threonine protein kinase gene, OsBIWNK1. The full-length cDNA of OsBIWNK1 is 2576bp with a predicted 2115bp open reading frame. OsBIWNK1 encodes a protein of 704 amino acids with a calculated molecular weight of 79.8KD and the isolectic point of 5.50. OsBIWNK1 gene is located on chromosome 7 of rice genome and consists of 7 exons and 6 introns. The deduced OsBIWNK1 protein contains a ser/thr protein kinase catalytic domain consisting of 11 conserved ser/thr protein kinase subdomains in the N-terminal, followed by a PWNK motif of about 60 amino acid, which was found in plant WNKs only. The conserved lysine (K) of subdomain II was replaced by the asparagines (N) as well as in Arabidopsis AtWNK1 protein. The amino acid sequence of OsBIWNK1 showed high levels of similarly to a number of protein kinases that belong to the WNK (with no lysine (K)) kinase group, and thus was named as OsBIWNK1 (Oryza sativa L. BTH indeced WNK1).To understand the function of OsBIWNK1 in disease resistance response, we performed a functional analysis of OsBIWNK1 in transgenic tobacco plants. The OsBIWNK1 coding region was cloned into a plant transformation binary vector pCHF3 under the control of the CaMV35s promoter and transformed tobacco leaf discs via agrobacterium-mediated feaf disc transformation. Ten kanamycin-resistant OsBIWNK1 transgenic tobacco lines were obtained and confirmed by PCR detection. Some transgenic lines overexpressing OsBIWNK1 showed morphological abnormalities in top-buds, axillary-shoot, leaf and delayed flowering, suggesting arole for OsBIWNKl in development process.