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

<i>Quercus robur</i> 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 <i>Q. robur</i>. 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., <i>MYO17</i>, <i>LEC2</i>) and down-regulation of defense-related DEGs (like <i>IOS1</i>, <i>Y3471</i>) 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 <i>CYP81Q32</i> and <i>CYP94A5</i>, and their coexpressed transcription factors (such as <i>WRKY6</i>, <i>WRKY53</i>) in Qr-T. The above findings suggest that leaf curling of <i>Q. robur</i> may weaken its insect resistance, which provides clues for improving plant resistance in agroforestry.