Molecular Cloning and Characterization of a Brassica napus L. MAP Kinase Involved in Oligochitosan-Induced Defense Signaling

Oligochitosan is a potent plant defense elicitor. In this paper, a novel Brassica napus mitogen-activated protein kinase (MAPK) gene induced by oligochitosan was isolated by rapid amplification of cDNA ends technique and designated as BnOIPK (oligochitosan-induced protein kinase (OIPK)). BnOIPK, with high sequence similarity to previously reported plant MAPK genes, encodes a 373-amino acid protein and belongs to the B subgroup of plant MAPK. Bioinformatics analysis showed BnOIPK contains one phosphorylation motif (TEY) and a conserved common docking domain in its C-terminal extension. With a constitutive expression in seedling leaves, BnOIPK is further upregulated upon treatment with plant hormone jasmonic acid (JA), but did not markedly respond to salicylic acid and abscisic acid. Activation of BnOIPK transcripts induced by oligochitosan depending on nitric oxide (NO) and hydrogen peroxide (H2O2) was identified by using NO, H2O2, and their scavenger, respectively. Polyclonal antibody BOK was prepared by using a 69-kD GST-BnOIPK fusion protein which was produced from pGEX-4T-1 vector. Western-blot assays showed BnOIPK could be induced by oligochitosan and JA at a short time. All these results suggest that BnOIPK might be a key node of JA-mediated defense signaling and act on the downstream of NO and H2O2.