Isolation and characterization of an oilseed rape MAP kinase BnMPK3 involved in diverse environmental stresses

A gene encoding mitogen-activated protein kinase was isolated from oilseed rape (Brassica napus) following drought treatment. The cloned gene, designated as BnMPK3 (GenBank accession no. AY642433), contains one phosphorylation motif (TEY) and a conserved CD domain in its C-terminal extension. BnMPK3 is highly homologous to AtMPK3 gene from Arabidopsis thaliana and belongs to the A-subgroup of mitogen-activated protein kinase. Semi-quantitative reverse transcription-polymerase chain reaction (RT-PCR) analyses showed that the expression level of BnMPK3 transcript was up-regulated by mannitol, NaCl, cold, H2O2, abscisic acid (ABA), salicylic acid (SA) and methyl jasmonate acid (m-JA). Interestingly, SA, m-JA enhanced gradually BnMPK3's expression all along after 20-60 min treatment, but its expression was all initiated by mannitol, NaCl, H2O2 and ABA in a short time and reached the highest level after 1-2 h treatment. Hysteresis of cold response showed that BnMPK3's expression was initiated after 1 h from normal growth conditions at room temperature to 4 °C, and reached the highest level after 6 h treatment. The inhibitors of MAPK activation PD98059 and U0126 did not inhibit BnMPK3 transcript. BnMPK3 was cloned into pYES2.1 and transformed into yeasts, and BnMPK3's expression enhanced yeasts' resistance to mannitol and peroxide in 600 mM mannitol and 0.2 mM tBuOOH drug assays. The present studies show that BnMPK3 is an early response gene involved in responses to biotic and abiotic stresses.