BpWRKY6 regulates insect resistance by affecting jasmonic acid and terpenoid synthesis in Betula platyphylla.

Forest pests and diseases pose serious threats to the sustainable development of forestry. Plants have developed effective resistance mechanisms through long-term evolution. Jasmonic acid and terpenoids play important roles in the defence response of plants against insects. Here, we discovered a transcription factor of the WRKY IIa subgroup, BpWRKY6, which is located in the nucleus, and the overexpression of BpWRKY6 in birch (Betula platyphylla) can increase resistance to gypsy moths (Lymantria dispar). The selective feeding results indicated that the gypsy moth tends to feed more on wild-type (WT) and mutant birch. The overexpression of BpWRKY6 decreased feeding, delayed development, inhibited CarE activity, and increased the activities of GST and CYP450 in gypsy moth larvae, whereas gypsy moth larvae that fed on the mutant birch presented the opposite trend. Further analysis revealed that BpWRKY6 directly binds to the promoters of jasmonic acid (JA) synthesis genes, including BpLOX15, BpAOC4, and BpAOS1, and the terpenoid synthesis gene BpCYP82G1, promoting their expression and increasing the contents of JA, 4,8,12-trimethyltrideca-1,3,7,11-tetraene (TMTT) and total terpenoids, thus affecting birch resistance to insects. In addition, BpWRKY6 was phosphorylated as a substrate for BpMAPK6, suggesting that BpWRKY6 functions through the MAPK signalling pathway. In conclusion, this study further improves the understanding of the insect defence response mechanism of plants to achieve green pest control and provide insect-resistant germplasm resources.