Enhancing Dual Fungal Resistance in Transgenic <i>Brassica napus</i> Through Heterologous Expression of <i>Perilla frutescens</i> Defensin PfPDF2

Plant defensins (PDFs), key components of the plant innate immune system, have important potential applications in the genetic engineering of crops for disease resistance. In this study, PfPDF2 was cloned from <i>Perilla frutescens</i> for the first time and introduced into <i>Brassica napus</i> through <i>Agrobacterium</i>-mediated transformation. The study showed that the transgenic plants were significantly more resistant to <i>Botrytis cinerea</i> and <i>Alternaria brassicae</i>, with a 50 to 87.7% reduction in lesion radius and a significant reduction in leaf yellowing after pathogen infestation. Molecular mechanism analysis indicated that PfPDF2 might activate the salicylic acid signaling pathway, induce the expression of disease resistance-related proteins, and participate in the regulation of photosynthesis and fatty acid metabolism. The number of branches and pods increased significantly in transgenic oilseed rape while maintaining a stable plant height, flowering time, and total yield, reflecting a dynamic balance between disease resistance, defense, and resource allocation. Despite the decrease in seed oil content, the elevated protein accumulation and remodeling of fatty acid fractions (increase in the ratio of oleic acid to stearic acid) provides a new direction for the development of functional lipids. This study identified and characterized the <i>PDF</i> gene of <i>P. frutescens</i> for the first time, revealing the disease resistance function of PfPDF2 in cruciferous crops and providing new insights into the application of PDFs in this crop group.