PagWRKY40 transcription factor improved insect resistance of Populus alba ×P. glandulosa

Forest pests and diseases exert serious impacts on the growth, development and yield of trees. In response to insect infestation, trees have evolved complex and interconnected regulatory pathways to induce plant defense responses. Metabolites such as jasmonic acid (JA) and flavonoids play important roles in plants defense against insects. In this study, we found that a transcription factor of the WRKY IIa subgroup, PagWRKY40, is localized in the nucleus. Insect feeding assays indicated that the overexpression of the PagWRKY40 in 84K poplar (Populus alba×Populus glandulosa) could enhance the resistance to the fall webworm (Hyphantria cunea) by reducing the feeding amount, increasing the activities of catalase (CAT), lipoxygenase (LOX), polyphenol oxidase (PPO), and elevating the contents of JA and flavonoids. RNA-seq analysis indicated that the differentially expressed genes (DEGs) between PagWRKY40-overexpressing (PagWRKY40-OE) plants and wild-type (WT) plants were significantly enriched in oxidase activity and the biosynthetic pathways of metabolites such as phenylpropane and flavonoids. Moreover, PagWRKY40 can directly bind to the W-box elements on the PagLOX3, PagCHI and PagPAL3 promoters to regulate the biosynthesis of JA and flavonoids, thereby enhancing the resistance of 84K poplar to fall webworm. In conclusion, these results indicate that PagWRKY40 is a transcription factor that positively regulates plant insect resistance defense, which can provide candidate germplasm resources for the breeding of new insect-resistant forest tree varieties in the future and lay the foundation for elucidating the mechanisms of plant insect resistance defense.