Function and regulation of a chitinase gene during Panax notoginseng defense response to root rot

Root rot severely affects Panax notoginseng, and an important causual pathogen is Fusarium solani. The pathogenesis-related proteins, including chitinase, are important for plant defenses against pathogens. In this study, a chitinase gene (PnCHI3) in P. notoginseng was isolated on the basis of published transcriptome data. Both the F. solani infection and exogenous methyl jasmonate treatment stimulated the expression of PnCHI3. In addition, the purified PnCHI3 recombinant protein had a significant inhibitory effect on root rot pathogens. Meanwhile, the resistance of transgenic tobacco over-expressing PnCHI3 was strengthened. The PnCHI3 promoter, which was cloned via genome walking, was employed to drive the GUS reporter gene expression in tobacco. Various signaling molecules, abiotic stresses, and fungal pathogens activated the PnCHI3 promoter. The results of an electrophoretic mobility shift assay and a yeast one-hybrid experiment revealed that the P. notoginseng transcription factor WRKY4 bound to the PnCHI3 promoter W-box cis-element and activated PnCHI3 transcription. In summary, the hormone signals including jasmonic acid and WRKY transcription factor enhances the expression of root rot resistance-related gene PnCHI3 in P. notoginseng in order to protect against invasion of F. solani.