In vivo competition assays between Vip3 proteins confirm the occurrence of shared binding sites in Spodoptera littoralis

Abstract

Due to their different specificity, the use of Vip3 proteins from Bacillus thuringiensis in combination with the conventionally used Cry proteins in crop protection is being essential to counteract the appearance of insect resistance. Therefore, understanding the mode of action of Vip3 proteins is crucial for their better application, with special interest on the binding to membrane receptors as the main step for specificity. Derived from in vitro heterologous competition binding assays using 125I-Vip3A and other Vip3 proteins as competitors, it has been shown that Vip3 proteins share receptors in Spodoptera frugiperda and Spodoptera exigua brush border membrane vesicles (BBMV). In this study, using 125I-Vip3Aa, we have first extended the in vitro competition binding site model of Vip3 proteins to Spodoptera littoralis. With the aim to understand the relevance (in terms of toxicity) of the binding to the midgut sites observed in vitro on the insecticidal activity of these proteins, we have performed in vivo competition assays with S. littoralis larvae, using disabled mutant (non-toxic) Vip3 proteins as competitors for blocking the toxicity of Vip3Aa and Vip3Af. The results of the in vivo competition assays confirm the occurrence of shared binding sites among Vip3 proteins and help understand the functional role of the shared binding sites as revealed in vitro.

Prioritization of absent quarantine pests in Brazil through the Analytical Hierarchy Process

“…Group 2 is formed by Tetranychus pacificus, Erwinia rhapontici, Rhodococcus fascians, Heterodera zeae, Pratylenchus scribneri, Sonchus arvensis, Arabis Mosaic Virus, Impatiens Necrotic Spot Virus, Spodoptera littoralis, and Platynota stultana, the last two stand out. These AQPs had the second and fifth-highest scores on the AHP, evidencing the effectiveness of the method since these pests are widely discussed in the literature due to the high impact caused on their hosts (Van der Gaag and Van der Straten, 2017;Lázaro-Berenguer et al, 2022).…”

Reduced binding associated with resistance to Vip3Aa in the corn earworm (Helicoverpa zea)

“…Considering that there is evidence that Vip3Aa binds to at least two sites in Spodoptera spp. (55,56), it is plausible that the reduced binding competition detected represents lack of binding to a subpopulation of Vip3Aa binding sites in CEW-Vip-RR. As expected, given the lack of cross-resistance to Cry1Ac, no alterations in Cry1Ac binding were detected in BBMV from CEW-Vip-RR compared to CEW-SS.…”