Insect Resistance in Quercus robur: A Comparative Metabolomic and Transcriptomic Analysis of Normal and Curly Leaf Varieties

Quercus robur is a tree species that produces acorns with rich nutritional value. Its leaf rolling is crucial for adapting to stress, but this trait’s impact on plant–insect interactions remains unknown. We compared the resistance phenotypes, metabolomic profiles, and transcriptomic data of the curly leaf (Qr-T) and normal-leaf (Qr-S) varieties of Q. robur. Findings revealed that Qr-T exhibited higher leaf area consumption under herbivory. Metabolomic analysis found lower levels of key defensive compounds like Questiomycin A, Caffeine, and Indoleacrylic acid in Qr-T. Transcriptomics revealed up-regulation of DEGs related to development (e.g., MYO17, LEC2) and down-regulation of defense-related DEGs (like IOS1, Y3471) in Qr-T. GO and KEGG analyses indicated that defense responses and the isoflavonoid biosynthesis pathway were suppressed in Qr-T. Coexpression network analysis identified coordinated down-regulation of defense-related genes, such as CYP81Q32 and CYP94A5, and their coexpressed transcription factors (such as WRKY6, WRKY53) in Qr-T. The above findings suggest that leaf curling of Q. robur may weaken its insect resistance, which provides clues for improving plant resistance in agroforestry.