Vitellogenin knockdown strongly affects cotton boll weevil egg viability but not the number of eggs laid by females

Abstract

Vitellogenin (Vg), a yolk protein precursor, is the primary egg nutrient source involved in insect reproduction and embryo development. The Cotton Boll weevil (CBW) Anthonomus grandis Boheman, the most important cotton pest in Americas, accumulates large amounts of Vg during reproduction. However, the precise role of this protein during embryo development in this insect remains unknown. Herein, we investigated the effects of vitellogenin (AgraVg) knockdown on the egg-laying and egg viability in A. grandis females, and also characterized morphologically the unviable eggs. AgraVg transcripts were found during all developmental stages of A. grandis, with highest abundance in females. Silencing of AgraVg culminated in a significant reduction in transcript amount, around 90%. Despite this transcriptional reduction, egg-laying was not affected in dsRNA-treated females but almost 100% of the eggs lost their viability. Eggs from dsRNA-treated females showed aberrant embryos phenotype suggesting interference at different stages of embryonic development. Unlike for other insects, the AgraVg knockdown did not affect the egg-laying ability of A. grandis, but hampered A. grandis reproduction by perturbing embryo development. We concluded that the Vg protein is essential for A. grandis reproduction and a good candidate to bio-engineer the resistance against this devastating cotton pest.

RNAi-mediated silencing of vitellogenin gene curtails oogenesis in the almond moth Cadra cautella

“…Moreover, the existence of some other remarkable characteristics such as conserved GL/ICG motifs and cysteine residues are similar to those that exist in other insect Vgs, including the lepidopterans [21,23,28,47,53,63,68]. In the CcVg protein sequence, the DGQR was positioned at 13 residues upstream of the GI/LCG motif that is conserved in almost all lepidopteran Vgs [47,64].…”

“…The dsRNA was formed. The MEGAscript 1 RNAi kit has been successfully used in several RNAi experiments [52][53][54]. A reaction of dsRNA (20 μL) was set in a standard PCR tube.…”

Nucleases as a barrier to gene silencing in the cotton boll weevil, Anthonomus grandis

“…Double-stranded RNA (dsRNA) is the RNAi trigger molecule that primes the post-transcriptional downregulation of a target gene [ 22 – 24 ]. Studies using this technology showed efficient silencing of several target genes through microinjection into larvae and adult CBW insects [ 1 , 25 , 26 ], whereas experiments involving the dsRNA oral uptake resulted in ineffective gene knockdown [ 18 ].…”

“…The uptake of dsRNA can be achieved by soaking, microinjection or feeding, and the RNAi signal is subsequently transported between cells and tissues [ 40 ]. In CBW, the dsRNA microinjection methodology is known to work well [ 1 , 25 , 26 ], while oral feeding is not so effective [ 18 ], and soaking methodology has not been tested. The oral ingestion of dsRNA is associated with some barriers, such as the exposure of the dsRNA to nucleases secreted in the gut juice, the gut pH, the dsRNA concentration and dsRNA resistance [ 38 , 41 , 42 ].…”

RNAi-Mediated Suppression of Laccase2 Impairs Cuticle Tanning and Molting in the Cotton Boll Weevil (Anthonomus grandis)

“…The development of RNAi-based technologies for the management of insect pests provides new tools for crop protection that can be highly species-specific and environmentally friendly. Genes that are essential for insect survival, fecundity and/or development have been proposed as good RNAi targets to be applied in the control of agricultural pests and vectors of diseases ( Bally et al, 2016 ; Coelho et al, 2016 ; Murphy et al, 2016 ; Macedo et al, 2017 ; Niu et al, 2017 ; Knorr et al, 2018 ; Lopez et al, 2019 ). We observed that disruption of cuticle tanning metabolic pathway by suppression of AgraLac2 transcripts caused severe morphological deformations in A. grandis and negatively affected insect development and molting, inducing high mortality rates.…”