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Abstract
20-Hydroxyecdysone (20E), the most important regulator for insect development, is also a major component in phytoecdysteroids in plants. Therefore, this plant-derived hormone is considered as a potential natural product for use in pest management. However, some insects show high resistance to it, and the molecular mechanism of their resistance is still unclear. In this study, we find that the cotton bollworm Helicoverpa armigera larvae show high tolerance to artificial foods containing up to 50 μg 20E without any detrimental effects on growth and development. High performance liquid chromatography analysis indicates that high efficiency to transform the ingested 20E through an ecdysteroid esterification pathway may contribute to the resistance. Furthermore, comparative transcriptome analysis of the larvae’s midgut after 20E treatment identifies two genes (long-chain-fatty-acid–CoA ligase, Long-FACL; sterol O-acyltransferase, SATF) involved in the pathway. Transcriptome and real-time PCR show the Long-FACL gene can be significantly induced by 20E, and this induction is only detected in the midgut. However, 20E has no effect on the transcript of the SATF gene. Moreover, the heterologously expressed protein of the SATF gene shows the ecdysteroid-22-O-acyltransferase activity that requires fatty acyl-CoA, which is produced by Long-FACL. Taken together, our results identify and demonstrate the genes involved in the ecdysteroid esterification pathway conferring high resistance to 20E in the cotton bollworm, H. armigera.
Highlights
Ecdysteroids are one of the most important hormones in insects
We found the high dosage of the hormone did not affect the growth and development of cotton bollworm larvae
The phytoecdysteroid is considered as defense to negatively affect herbivore growth and survival
Summary
Ecdysteroids are one of the most important hormones in insects. They are recognized as essential regulators controlling molting, metamorphosis, and reproduction in insects. Since the isolation of ecdysone from silkworm pupae in 1954, ecdysteroid analogs called phytoecdysteroids were discovered in plant species (Butenandt and Karlson, 1954; Nakanishi et al, 1966; Lafont and Horn, 1989; Dinan, 2001). Phytoecdysteroids are considered to be a defensive system to protect plants against phytophagous invertebrates (Adler and Grebenok, 1999; Mithöfer and Boland, 2012). In this regard, phytoecdysteroids were demonstrated to be antifeedants toward some insects, such as the dark-winged fungus gnat (Bradysia impatiens) and polyphagous Japanese beetle Popillia japonica (Schmelz et al, 2002; Jurenka et al, 2017). Phytoecdysteroids have been suggested to be a good candidate for pest management (Soriano et al, 2004; Aly et al, 2011; Jurenka et al, 2017; Chaubey, 2018)
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