Functional analysis of a downregulated guanylate kinase gene associated with the mechanism of action of 6‐methylcoumarin against the whitefly Bemisia tabaci

Abstract BACKGROUND 6‐Methylcoumarin is a botanical compound that displays prominent activity against Bemisia tabaci. The guanylate kinase (GUK) is vital for maintaining intracellular Ca 2+ equilibrium. Downregulation of GUK gene expression has been observed in B. tabaci exposed to 6‐methylcoumarin. However, the insecticidal mechanism of 6‐methylcoumarin against B. tabaci remains unclear. RESULTS 6‐Methylcoumarin, in both greenhouse and field assays, possessed excellent control efficacy against whitefly. In addition, 6‐methylcoumarin significantly induced intracellular Ca 2+ overload. Furthermore, RNA sequencing, Quantitative Polymerase Chain Reaction, and Western blotting analyses revealed that the GUK gene was significantly downregulated after 6‐methylcoumarin treatment in whiteflies. Importantly, RNA interference‐mediated silencing of the GUK gene increased the susceptibility of B. tabaci to 6‐methylcoumarin. Moreover, molecular docking and microscale thermophoresis suggested that GUK amino acids TYR55, TYR83, ALA76 and ILE104 may be crucial binding sites for 6‐methylcoumarin, exhibiting strong interactions ( K d = 3.27 μM). This binding likely distorts the GUK structure, implying that it exerts its potential function against whiteflies by directly targeting the GUK protein. CONCLUSIONS This study elucidates the insecticidal mechanism of 6‐methylcoumarin, which involves the inhibition of GUK transcription and disruption of Ca 2+ homeostasis. These findings suggest that 6‐methylcoumarin may be a promising environmentally friendly candidate for B. tabaci control. © 2025 Society of Chemical Industry.