Increasing Anthonomus grandis susceptibility to Metarhizium anisopliae through RNAi‐induced AgraRelish knockdown: a perspective to combine biocontrol and biotechnology

Abstract

BACKGROUND The hemolymph and insect gut together have an essential role in the immune defense against microorganisms, including the production of antimicrobial peptides (AMP). AMPs are mainly induced by two specific signaling pathways, Toll and immune deficiency (IMD). Here, we characterize the expression profile of four genes from both pathways and describe the importance of AgraRelish in the immune defense of Anthonomus grandis against the entomopathogenic fungus Metarhizium anisopliae by RNA interference (RNAi). RESULTS To characterize the pathway that is activated early during the A. grandis–M. anisopliae interaction, we assessed the expression profiles of AgraMyD88 and AgraDorsal (Toll pathway), AgraIMD and AgraRelish (IMD pathway), and several AMP genes. Interestingly, we found that IMD pathway genes are upregulated early, and Toll pathway genes are upregulated just 3 days after inoculation (DAI). Furthermore, nine AMPs were upregulated 24 h after fungus inoculation, including attacins, cecropins, coleoptericins, and defensins. AgraRelish knockdown resulted in a reduction in median lethal time (LT50) for M. anisopliae‐treated insects of around 2 days compared to control treatments. In addition, AgraRelish remained knocked down at 3 DAI. Finally, we identified that AgraRelish knockdown increased fungal loads at 2 DAI compared to control treatments, possibly indicating a faster infection. CONCLUSIONS Our data indicate the influence of the IMD pathway on the antifungal response in A. grandis. Combining biocontrol and RNAi could significantly improve cotton boll weevil management. Hence, AgraRelish is a potential target for the development of biotechnological tools aimed at improving the efficacy of M. anisopliae against A. grandis.

Transgenic plants expressing immunosuppressive dsRNA improve entomopathogen efficacy against Spodoptera littoralis larvae

“…Chen and coworkers have demonstrated that recombinant Isaria fumosorosea fungi expressing dsRNA targeting an immune gene (i.e., Toll-like receptor 7) in Bemisia tabaci are more virulent against this pest (Chen et al 2015). Similarly, RNAi silencing of AgraRelish, a transcription factor of the IMD pathway in the Coleoptera Anthonomus grandis, improves the efficacy of the fungus Metarhizium robertsii (Moreira-Pinto et al 2021). Interestingly, molecules of parasitic origin that impair immune responses in lepidopteran larvae have been proven to enhance entomopathogen performance against these insects.…”

Why are there no widely successful microbial bioherbicides for weed management in crops?

“…This concept was successfully demonstrated with microbial bioinsecticide by combining an RNAi for the insect immune deficiency pathway with the entomopathogenic fungus Metarhizium anisoplise. 66 The result was faster and more virulent infection of the cotton boll weevil (Anthonomus grandis) by the microbe. However, there have been no commercial successes in the use of RNAi to silence weed genes.…”

“…Another possibility is to use appropriate RNA interference (RNAi) to knockout plant defense and increase the efficacy of a microbial bioherbicide. This concept was successfully demonstrated with microbial bioinsecticide by combining an RNAi for the insect immune deficiency pathway with the entomopathogenic fungus Metarhizium anisoplise 66 . The result was faster and more virulent infection of the cotton boll weevil ( Anthonomus grandis ) by the microbe.…”

Simultaneous silencing of juvenile hormone metabolism genes through RNAi interrupts metamorphosis in the cotton boll weevil

“…While a moderate RNAi response is observed following the injection of small amounts of dsRNA in the CBW ( Macedo et al, 2017 ; Firmino et al, 2020 ; Moreira-Pinto et al, 2021 ), large amounts of dsRNA are required to produce strong and persistent gene silencing that culminates in clear phenotypic effects when the dsRNA is delivered through feeding ( Garcia et al, 2017 ). Therefore, the relatively weak RNAi response of CBW upon dsRNA treatment hampers the functional analysis of genes through the RNAi approach and the selection of potential target genes that could be used in the development of RNAi-mediated control methods.…”