Defence induction and identification of key genes associated with Lymantria dispar oral secretions in Populus davidiana × P. bolleana on the basis of transcriptome and hormone levels

Abstract

In the constant battle with herbivorous insects, plants have evolved sophisticated recognition and adaptation mechanisms to fight insect attacks. Insect infestation is a major challenge in poplar afforestation production. In this study, we mimicked insect feeding by applying insect oral secretions (OS) to the leaf mechanical wounds of Populus davidiana × P. bolleana and combined transcriptome and hormone analyses to investigate the effects of OS from Lymantria dispar on defence responses and to identify the key genes involved in Populus davidiana × P. bolleana defence. Our results revealed that 3067 differentially expressed genes were involved in the OS-induced response to wounding in Populus davidiana × P. bolleana. OS treatment can rapidly induce the expression of genes related to the jasmonic acid (JA) biosynthetic and signal transduction pathways. The contents of JA, jasmonoyl-l-isoleucine, indole-3-acetic acid and salicylic acid significantly increased in response to OS. To construct a coexpression gene network, a hub gene annotated as WRKY22 was identified in Populus davidiana × P. bolleana. To investigate the function of the PdbWRKY22 gene against pests, PdbWRKY22 was successfully transformed into Populus davidiana × P. bolleana. Transient overexpression of PdbWRKY22 induced JA-related gene expression and suppressed the feeding behaviour of L. dispar larvae under OS treatment. These results suggested the defence mechanism of Populus davidiana × P. bolleana against L. dispar at the transcriptional and hormonal levels, and revealed that PdbWRKY22 plays a crucial physiological role in Populus davidiana × P. bolleana.