Exploring the Terminal Pathway of Sex Pheromone Biosynthesis and Metabolism in the Silkworm

SIMPLE SUMMARY: Insect sex pheromone biosynthesis has received widespread attention, while the terminal pathway related to aldehyde synthesis and metabolism is still poorly understood at a molecular level. Previous studies found that the silkworm, Bombyx mori (Lepidoptera, Bombycidae), has two pheromone compounds, bombykol and bombykal, with a ratio of 11:1, while its closest wild relative, B. mandarina, only uses bombykol as a pheromone. In this study, sex pheromone gland transcriptomes were compared between the domestic and wild silkworms. All the candidate gene families were identified. Then we used the differentially expressed information, tissue and developmental expression profiles, and phylogenetic analysis to identify the putative causal genes involved in the terminal pathway. Our findings provide insights into the aldehyde synthesis and metabolism pathways and evolutionary conservation in moths. ABSTRACT: Sex pheromones are vital to sexual communication and reproduction in insects. Although some key enzymes in pheromone production have been well studied, information on genes involved in the terminal pathway is limited. The domestic silkworm employs a pheromone blend containing (E,Z)-10,12-hexadecadienol (bombykol) and analogous (E,Z)-10,12-hexadecadienal (bombykal); whereas, its wild ancestor B. mandarina uses only bombykol. The two closely related moths might be a good model for exploring the genes involved in aldehyde pheromone synthesis and metabolism. By deep sequencing and analyzing the sex pheromone gland (PG) transcriptomes; we identified 116 candidate genes that may be related to pheromone biosynthesis, metabolism, and chemoreception. Spatiotemporal expression profiles and differentially expressed analysis revealed that four alcohol oxidases (BmorAO1; 2; 3; and 4); one aldehyde reductase (BmorAR1); and one aldehyde oxidase (BmorAOX5) might be involved in the terminal pathway. Phylogenetic analysis showed that, except for BmorAO3 and MsexAO3, AOs did not show a conversed orthologous relationship among moths; whereas, ARs and AOXs were phylogenetically conserved. This study provides crucial candidates for further functional elucidation, and which may be utilized as potential targets to disrupt sexual communication in other moth pests.