Osmotin and osmotin-like proteins (OLPs) play important roles in plant defense responses. The full-length cDNA sequence of an OLP gene was cloned from Panax notoginseng using rapid amplification of cDNA-end technology and named PnOLP1. A quantitative reverse transcription-PCR analysis showed that the signaling molecules methyl jasmonate, salicylic acid, ethylene, and hydrogen peroxide induced PnOLP1 expression to different degrees. In addition, the expression level of PnOLP1 rapidly increased within 48 h of inoculating P. notoginseng with the root rot pathogen Fusarium solani. Subcellular localization revealed that PnOLP1 localized to the cell wall. A prokaryotic expression vector containing PnOLP1 was constructed and transformed into Escherichia coli BL21 (DE3), and in vitro antifungal assays were performed using the purified recombinant PnOLP1 protein. The recombinant PnOLP1 protein had strong inhibitory effects on the mycelial growth of F. oxysporum, F. graminearum, and F. solani. A plant PnOLP1-overexpression vector was constructed and transfected into tobacco, and the resistance of T2 transgenic tobacco against F. solani was significantly enhanced compared with wild-type tobacco. Moreover, a PnOLP1 RNAi vector was constructed and transferred to the P. notoginseng leaves for transient expression, and the decrease of PnOLP1 expression level in P. notoginseng leaves increased the susceptibility to F. solani. Thus, PnOLP1 is an important disease resistance gene involved in the defense responses of P. notoginseng to F. solani.
Keywords: antifungal activity; elicitors; osmotin-like protein; overexpression in tobacco; root rot.