Roles of Hormones, Calcium and PmWRKY31 in the Defense of Pinus massoniana Lamb. Against Dendrolimus punctatus Walker

Dendrolimus punctatus Walker is a major pest affecting Pinus massoniana Lamb. forests and can cause serious economic and ecological losses. WRKY transcription factors play important roles in coping with various environmental stresses and plant responses against herbivorous insects. However, the mechanisms underlying the actions of WRKY in the defense responses of D. punctatus in P. massoniana are still unclear. Our previous study provided evidence that WRKY plays an important role in the insect resistance of P. massoniana. In this study, the treatments of exogenous hormones and Ca2+ increased the concentrations of endogenous hormones, and terpenoid synthases in P. massoniana effectively improving its resistance to D. punctatus. After analyzing the WRKY family of P. massoniana, PmWRKY31 was selected and studied. A direct interaction between PmWRKY31 and PmLp8 was observed by yeast double hybridization assay. Gene expression analysis showed that treatments of exogenous hormones and Ca2+ induced high PmWRKY31 expression. The expression pattern of PmWRKY31 was different under treatment of MeJA compared to those of GA, ABA and SA. These results indicated that PmWRYK31 and PmLp8 interacted with each other to promote the expression of terpenoid synthase genes and increase the content of terpenoid volatile substances by regulating the gene expression of hormone signaling pathways, to improve the ability of P. massoniana to resist D. punctatus, providing theoretical support for the involvement of WRKY transcription factors in enhancement of the insect resistance of P. massoniana through their regulation of hormone signaling.