Plant defensin gene PfPDF2 from Perilla frutescens confers high-level resistance to Alternaria brassicae and Botrytis cinerea in Brassica napus

Background: Plant defensins (PDF) are a group of small cysteine-rich peptides with broad-spectrum antimicrobial activity that play important roles in the response of plant to abiotic stresses. Results: In this study, Perilla frutescens PDF ( PfPDF ) genes were identified and functionally characterized. A total of 6 PfPDF genes were successfully cloned. Characterization analysis revealed that all PfPDF genes consisted of 2 exons and 1 intron and encoded 73 ~ 88 amino acids, each of which contained 8 cysteine residues. Phylogenetic analyses indicated that all PfPDFs were members of the PDF type I family. The expression of PfPDF genes showed wide tissue specificity. PfPDF1 , PfPDF2 and PfPDF4 were expressed in stems, leaves, flowers and seeds, and PfPDF3 was expressed in leaves and seeds, while PfPDF5 and PfPDF6 were only expressed in seeds. Subsequently, PfPDF2 , which was highly expressed in seeds, was transformed into Brassica napus to obtain transgenic plants. The total yield of transgenic B. napus was comparable to that of wild-type. Moreover, an in vitro antifungal bioactivity test on leaves revealed that the resistance to Alternaria brassicae and Botrytis cinerea was enhanced significantly in PfPDF2 -overexpressing B. napus compared to that of the wild type. Analysis of differentially expressed genes in wild-type and transgenic B. napus showed that photosynthesis, fatty acid biosynthesis and metabolism pathways were significantly activated. Conclusions: Overall, this study identified and characterized PDF genes from P. frutescens for the first time and clarified that PfPDF2 could be applied to produce crops with higher resistance to pathogens, providing unique insights and new genetic resources for molecular breeding.