Biosynthesis
Insect pheromones play an important role in the exchange of information between insect individuals and communities. The chemical properties of pheromones have been determined, and most pheromones are composed of two or more related molecules. In order to interfere with the biosynthesis of insect pheromones and interrupt chemical communication signals to achieve the purpose of controlling pests, in-depth research on the biosynthetic pathway and regulation of insect pheromones is crucial.
The biosynthetic chemistry of insect pheromones will be described from precursors for pheromones, site of pheromone synthesis, specific enzymes and biosynthesis of sex pheromones in moth.
Precursors for Pheromones
Pheromone precursors refer to the starting materials or intermediates that insects use to synthesize pheromones. According to different sources, Precursors for pheromones can be divided into three categories.
De novo synthesis ( the synthesis of complex molecules from simple molecules ).
Conversion of precursors provided by the host plant or substrate.
Direct incorporation of molecules found from the host.
Site of Pheromone Synthesis
Sex pheromones are produced by various organs in specific structures of insects and the sites of pheromone synthesis vary from insect to insect. Knowing the specific sites of pheromone synthesis and secretion is a prerequisite for extracting and isolating pheromones [1].
Oenocytes
Pheromones are often produced by specialized secretory cells called oenocytes.
Glands
The females of most moths produce sex pheromones in glands.
Ejaculatory bulb
Male Drosophila produce sex pheromones in the ejaculatory bulb.
Other
Ants use multiple glands like Dufour, poison, pygidial and mandibular glands.
Enzymes in Pheromone Biosynthesis
Biosynthesis of Sex Pheromones in Moth
Fatty acid synthesis
In sex pheromone synthesis, the fatty acid synthesis process is the same as that in general metabolism. The key enzymes in the synthesis are acetyl-CoA carboxylase as well as fatty acid synthase.
Fatty acid transport
Sex pheromone precursors are transported into pheromone gland (PG) by fatty acid transport protein (FATP), which provides the raw material for subsequent sex pheromone synthesis.
Carbon chain shortening
It is generally believed that the pathway for generating moth sex pheromone precursors with different carbon chain lengths is similar to the peroxisomal fatty acid β-oxidation in vertebrates.
Desaturation reaction
Desaturases can remove hydrogen atoms at specific positions and introduce double bonds, resulting in the formation of cis-trans isomers. Differences in desaturases can lead to differences in the components of sex pheromones, leading to species differentiation.
Modification of functional groups
After carbon chain shortening and desaturation reactions to form sex pheromone intermediates with specific lengths and suitable double bond positions, these sex pheromone precursors form functional groups such as alcohols, aldehydes, esters and so on through various enzymes.
Generation of pheromone mixtures in specific ratios
Since pheromone is a product of mixing different components in a certain proportion and dosage, it has a high degree of species specificity. The production of pheromone mixture requires the cooperation of desaturase, reductase, oxidase, or acyltransferase.
In the regulation of moth sex pheromone synthesis and release, PBAN (pheromone biosynthesis activating neuropeptides) plays an important role that can regulate the production of female moth sex pheromone by affecting enzymes in the biosynthetic pathway. Other substances can also indirectly induce the production of pheromones by regulating the activity of PBAN, such as juvenile hormone, etc.
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Reference
- Yew, J. Y.; Chung, H. Insect pheromones: An overview of function, form, and discovery. Prog Lipid Res. 2015. 59