Isolation and functional characterization of a pathogenesis-related protein 4 gene from Panax notoginseng

Pathogenesis-related (PR) proteins are a large class of proteins that accumulate in plant cells in response to multiple biotic and abiotic stresses. Root rot is an important disease of the perennial medicinal plant Panax notoginseng, with Ilyonectria destructans identified as one of the causative pathogens. However, little is known about the PR-encoding genes expressed during the infection of P. notoginseng by I. destructans. In this study, we isolated a PR4 gene from P. notoginseng(PnPR4) on the basis of a genomic analysis. The expression of this gene was significantly up-regulated in the roots of I. destructans-infected P. notoginseng plants at 72 h post-inoculation (relative to the control level). The expression of PnPR4 was affected by hydrogen peroxide, gibberellic acid, ethephon, abscisic acid, and salicylic acid. The transient expression of the PnPR4-GFP fusion gene in tobacco epidermal cells indicated that PnPR4 was localized in the cell wall (i.e., extracellular protein). In addition, the purified PnPR4 recombinant protein had antifungal activities, with inhibitory effects on I. destructans. Furthermore, the PnPR4 gene was transferred into the model plant tobacco to verify its function. The overexpression of PnPR4 increased the resistance to I. destructans. In conclusion, PnPR4 contributes to the defense response of P. notoginseng to I. destructans.