Abstract: Oligochitosan prepared by enzymatic hydrolysis of chitosan is a potential plant defense elicitor, but how the oligochitosan induces the resistance of plants to pathogens is still unclear. So we try to explore the signal transduction pathways of oligochitosan inducing defense. We isolated a new cDNA coding for mitogen-activated protein kinase (MAPK), designated BnMPK4 (GenBank: DQ206628), from oilseed (Brassica napus L.) based on our former microarray data. BnMPK4 encodes a 373-amino-acid protein with high sequence similarity to previously reported plant MAPK genes such as AtMPK4 and belongs to the B subgroup of plant MAPK. Bioinformatic analysis showed BnMPK4 contains one phosphorylation motif (TEY) and a conserved CD domain in its C-terminal extension. By using Semi-Quantitative RT-PCR technique we found that BnMPK4 had a constitutive expression in seedling leaves and was further up-regulated by treatment with plant hormone jasmonic acid (JA) and fungal elicitor oligochitosan but did not respond to salicylic acid (SA) and abscisic acid (ABA). These results suggest a role for BnMPK4 in oligochitosan-induced and JA/ET-regulated defense signalling pathway.

Key words: Oligochitosan, Brassica napus L., BnMPK4, JA/ET signaling pathway