Transcriptomic and Metabolomic Joint Analysis to Explore the Molecular Mechanisms of Different Resistant Poplar Varieties in Response to the Feeding Damage of Anoplophora glabripennis

In China, Asian longhorned beetle (ALB) infestations severely threaten poplar resources, the primary species used for shelterbelt afforestation. Two fast-growing poplar hybrids, Populus alba × (P. alba × P. glandulosa) (QB3) and P. nigra × P. deltoids (Ta), exhibit contrasting ALB resistance: QB3 is resistant, while Ta is highly susceptible. To elucidate the underlying molecular mechanisms, we examined transcriptome and metabolome changes in QB3 and Ta after ALB feeding. Transcriptomic analysis revealed significantly differential expressions of MKK9, EBF1, and PRB1 genes between QB3 and Ta under both control and infested conditions, with enrichment in the plant MAPK signaling pathway. Following insect herbivory, QB3 upregulated LOX3.1, ACX3, AOS3, PED1, and JMT genes, enriched in α-linolenic acid metabolism. Metabolomic profiling showed significant variations in α-linolenic acid abundance. After ALB feeding, QB3 exhibited a marked increase in α-linolenic acid content compared to Ta, while γ-linolenic acid levels remained unchanged. Both genotypes showed elevated jasmonoyl-isoleucine (JA-Ile) concentrations, with QB3 displaying extremely significant increases versus moderately significant increases in Ta. These results offer insights into poplar tree responses to ALB feeding damage.