Identification and Characterization of Genes Involved in Ecdysteroid Esterification Pathway Contributing to the High 20-Hydroxyecdysone Resistance of Helicoverpa armigera

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.

Identification of Genes Involved in Resistance to High Exogenous 20-Hydroxyecdysone in Spodoptera litura

“…For long-chain-fatty-acid–CoA ligase (Long-FACL), the enzyme catalyzes the formation of fatty acyl-CoA, which is involved in various metabolic and regulatory processes. More importantly, our previous study proved the product of Long-FACL could be used as an acyl-group donor to enhance the ecdysteroid-22-O-acyltransferase activity of sterol O-acyltransferase (SATF) [ 35 ]. In summary, S. litura larvae could utilize almost all known ecdysteroid degradation related enzymes to detoxify the exogenous 20E.…”

“…S. litura and H. armigera belong to noctuid insects, and both show high resistance to phytoecdysteroids [ 35 ]. Our previous study indicated the ecdysteroid esterification pathway was the main process to detoxify exogenous 20E for H. armigera [ 35 ].…”

“…S. litura and H. armigera belong to noctuid insects, and both show high resistance to phytoecdysteroids [ 35 ]. Our previous study indicated the ecdysteroid esterification pathway was the main process to detoxify exogenous 20E for H. armigera [ 35 ]. To compare genes affected by 20E treatment between S. litura and H. armigera , we performed comparative transcriptomic analysis using RNA-seq data from this study and our previous published paper [ 35 ].…”

“…Our previous study indicated the ecdysteroid esterification pathway was the main process to detoxify exogenous 20E for H. armigera [ 35 ]. To compare genes affected by 20E treatment between S. litura and H. armigera , we performed comparative transcriptomic analysis using RNA-seq data from this study and our previous published paper [ 35 ]. For 20E up-regulated genes, S. litura and H. armigera shared 50.6%% (80/158) genes ( Figure 5 A).…”

“…Therefore, it is broadly accepted that the phytoecdysteroid serves as a defender to resist herbivores [ 6 , 37 , 38 ]. However, some insects have also developed strategies to overcome the defensive system during their long coexistence with plants [ 13 , 15 , 35 ]. To better understand how insects adapt to the phytoecdysteroid of their host plants, we demonstrated how the physiology and gene expression levels change after 20E treatment in S. litura larvae.…”