Isolation of a novel Ser/Thr protein kinase gene from oligochitosan-induced tobacco and its role in resistance against tobacco mosaic virus

Oligochitosan induces defense responses to pathogenic microbes in a wide variety of plants by acting as an elicitor. In the present study, mRNA differential display was used to investigate oligochitosan-induced transcriptional activation of defense-related genes. Accordingly, a novel Ser/Thr protein kinase gene was isolated and designated as oligochitosan-induced protein kinase (oipk). Molecular cloning showed that oipk contains six introns interrupted by seven exons. The open reading frame (ORF) of the gene is 1848 bp, which encodes a putative protein of 615 amino acids with the predicted molecular mass of 70.96 kDa and a pI of 6.32. A plant oipk antisense expression vector was constructed and transformed into tobacco by Agrobacterium tumefaciens. Decreased phenylalanine ammonia-lyase (PAL, EC 4.3.1.5) activity and decreased resistance to tobacco mosaic virus (TMV) were observed in transgenic tobacco. RT-PCR analysis revealed that oipk was expressed at high levels after oligochitosan induction in wild-type tobacco, but not in transgenic tobacco. These results indicated that oipk is involved in the signal pathway of oligochitosan-induced resistance in tobacco.