Expression and Biological Assay of HrpN in Pichia pastoris

HrpN gene was placed under the control of AOX1 promoter in a Pichia expression vector pPIC6αA. Through electroporation transformation of X-33 Pichia and Blasticidin selection, a strain of Pichia pastoris capable of secreting harpin_Ea into the medium at high level was obtained. After initially purified, SDS-PAGE analysis of the expression products indicated that harpin_Ea was secreted at high level when the Pichia pastoris expression clone had been induced for 96 hours. The results of bioassay showed that the recombinant harpin_Ea had the ability of eliciting hypersensitive response in tobacco. The activity of this harpin_Ea is higher than that of harpin_Ea expressed in Escherichia coli.