Salicylic Acid Biosynthesis via PdCBP60E Confers Anoplophora glabripennis Resistance in Populus deltoides 'Shalinyang'.

Anoplophora glabriformis (ALB) is one of the most destructive wood-boring insects attacking poplars. Populus deltoides 'Shalinyang' (PdS) is an ALB-resistant species, but the specific molecular mechanisms of ALB resistance are unclear. Here, metabolomics showed that salicylic acid (SA) content increased significantly after ALB infection, and exogenous SA also increased the activity of defense enzymes in PdS. Therefore, the PdCBP60E gene related to SA synthesis was obtained from the PdS. The expression of the upstream PdPAD4 and downstream PdICS1 genes of PdCBP60E increased by 152.48% and 371.26% with ALB infestation, respectively. The SA content, CAT, SOD, and POD activities in transgenic Arabidopsis thaliana increased by 211.3%, 48.3%, 21.3% and 98.0%, respectively. However, VIGS-mediated silencing of PdCBP60E resulted in a 47.4% reduction in PdCBP60E transcript levels and a 41.6% decrease in SA content, respectively. Concurrently, this suppression induced regulatory changes within the SA pathway, characterized by increased PdPAD4 expression and decreased PdICS1 expression. Insect resistance assays further revealed that ALB adults displayed a significantly stronger feeding preference for PdS-silenced plants, with stem damage severity increasing by 193.9%. Additionally, larvae feeding on silenced plants exhibited 28.2% greater biomass accumulation, coupled with elevated activities of digestive enzymes (pectase: increased 78.7%; cellulase: increased 75.3%) and peroxidase (POD: increased 69.1%) compared to those on control plants. Overall, we obtained evidence that PdCBP60E was a positive regulator in ALB resistance improvement in PdS, providing comprehensive insights into the poplar defense system to pest infestation.