20‐Hydroxyecdysone regulates the prophenoloxidase cascade to immunize Metarhizium anisopliae in Locusta migratoria

Abstract

BACKGROUNDPPO (prophenoloxidase) cascade plays an important role in resisting invasion of entomogenous fungus. The 20‐hydroxyecdysone (20E) exerts potent effect on the innate immunity in many insects. However, whether 20E controls the PPO cascade system against fungi and the regulatory mechanism in insects remains unclear.RESULTSIn this study, both the proteome and transcriptome of Locusta migratoria were determined followed by the induction of 20E. Pattern recognition receptor GNBP‐2 (Gram‐negative binding proteins) has been identified that responded to 20E at both messenger RNA (mRNA) and protein levels. The PPO gene expression in fat body and PO (phenoloxidase) activity in plasma was found significantly induced after 20E injection and during the high‐20E developmental stage. However, when 20E signal was blocked by RNA interference (RNAi) of ecdysone receptor, the expression level of PPO and PO activity failed to be increased by 20E. Thus, 20E could not significantly induce the expression of PPO gene and PO activity after RNAi of GNBP‐2. Furthermore, 20E treatment notably enhanced the resistance of L. migratoria against Metarhizium anisopliae. Followed by of GNBP‐2 silencing, the mortality of nymphs was significantly increased under the stress of Metarhizium anisopliae, and 20E injection could not increase the resistance.CONCLUSIONThe 20E regulates the PPO system to resist fungal invasion via regulating GNBP‐2 in worldwide pest L. migratoria. Our results provide insight into the mechanism of how 20E enhances the antimicrobial immunity, and will be beneficial for modification of entomogenous fungi targeting on hormones and the immune system. © 2020 Society of Chemical Industry

The cecropin-prophenoloxidase regulatory mechanism is a cross-species physiological function in mosquitoes

“…During the onset of metamorphosis, 20E initiates various early gene expression cascades and induces the formation of the pupal cuticle in order to regulate the insect’s developmental transitions ( Dong et al., 2003 ; King-Jones et al., 2005 ; Yamanaka et al., 2013 ). Previous studies have demonstrated that 20E modulates the cellular and humoral innate immunity of insects ( Flatt et al., 2008 ; Tian et al., 2010 ; Sun et al, 2016 ) by priming the production of various effector genes, including cecropins ( Reynolds et al., 2020 ; Nunes et al., 2020 ) and PPOs ( Han et al, 2020 ; Reynolds et al., 2020 ). The results of Liu et al.…”

Azadirachtin interferes with basal immunity and microbial homeostasis in the Rhodnius prolixus midgut

“…This effect was reversed by the addition of exogenous ecdysone in the insect blood meal, suggesting that the hormone regulates the IMD pathway. Likewise, it has been suggested that the IMD pathway is under hormonal regulation in Drosophila (Flatt et al, 2008;Rus et al, 2013;Zheng et al, 2018) and in Locusta migratoria (Han et al, 2020;Han et al, 2017), in which ecdysone activates the expression of genes encoding a peptidoglycan recognition protein LC (PGRP-LC). Genomic and transcriptomic analyses highlighted the presence of some, but not all, genes encoding components of the IMD pathway in R. prolixus (Nishide et al, 2019;Ribeiro et al, 2014;Zumaya-Estrada et al, 2018).…”

“…Besides its role in insect development and reproduction, ecdysone is also associated with the regulation of the immune system in various species (Ahmed et al, 1999;Dimarcq et al, 1997;Han et al, 2020;Han et al, 2017;Ma et al, 2019;Meister and Richards, 1996;Tian et al, 2010). In Drosophila melanogaster, ecdysone has a role in the insect's humoral response; both in vivo and in vitro treatments with ecdysone increase levels of expression of antimicrobial peptides (AMPs) (Flatt et al, 2008;Rus et al, 2013;Zhang and Palli, 2009).…”

Host–Pathogen Interactions between Metarhizium spp. and Locusts

“…The total PO activity of desert locusts gradually decreased with M. acridum infection [ 119 ]. Except for the PPO activation system, PPO transcription expression is responsive to infection by Metarhizium and is regulated by hormones and two genes likewise [ 87 , 120 ]. 20E further promoted the expression of GNBP2 to increase PPO expression in the fat body of locusts infected with M. anisopliae [ 120 ].…”

“…Except for the PPO activation system, PPO transcription expression is responsive to infection by Metarhizium and is regulated by hormones and two genes likewise [ 87 , 120 ]. 20E further promoted the expression of GNBP2 to increase PPO expression in the fat body of locusts infected with M. anisopliae [ 120 ]. Decreased expression of IAP boosted PO activity during infection by M. acridum .…”