Biology subjects

Jurat-Fuentes, J. L.

Publications and source records attributed to Jurat-Fuentes, J. L..

4 recordsLinked to original sources

bioRxiv2025

Reduced processing and toxin binding associated with resistance to Vip3Aa in a resistant strain of fall armyworm (Spodoptera frugiperda) from Louisiana

BackgroundTransgenic crops expressing Cry and Vip3Aa insecticidal proteins from the bacterium Bacillus thuringiensis are a primary tool for controlling fall armyworm (Spodoptera frugiperda) populations. The evolution of resistance to Cry proteins in the native range of the fall armyworm has increased reliance and intensified the selection of resistance to Vip3Aa. In this study, we identified mechanisms of resistance to Vip3Aa in the LA-RR strain of S. frugiperda originating from Louisiana (USA). ResultsMidgut epithelial damage in susceptible larvae was evidenced by a significant drop in midgut pH after feeding on either Vip3Aa protoxin or activated toxin. In contrast, this midgut pH drop was only detected for activated Vip3Aa toxin in LA-RR larvae. Midgut fluids from LA-RR larvae displayed delayed processing of Vip3Aa protoxin when compared to fluids from susceptible larvae, and this slower processing was associated with reduced activity and expression of trypsin and chymotrypsin enzyme genes in the LA-RR strain. In bioassays, LA-RR larvae were significantly more susceptible to Vip3Aa protoxin pre-processed by midgut fluids from susceptible than from LA-RR larvae. In addition, midgut brush border membrane vesicles from LA-RR larvae exhibited lower specific Vip3Aa toxin binding than vesicles from the susceptible strain. ConclusionThe results of this study support that both slower proteolytic processing and reduced specific binding are associated with resistance to Vip3Aa in an S. frugiperda strain from the Western hemisphere, the native range of this pest. This information increases our understanding of resistance to Vip3Aa and advances monitoring and fall armyworm management.

plant biology↗

bioRxiv2023

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

Transgenic corn and cotton expressing Cry and Vip insecticidal proteins from the bacterium, Bacillus thuringiensis (Bt), have been a valuable tool for the management of lepidopteran pests. In 2019, a Vip3Aa-resistant strain of Helicoverpa zea (CEW-Vip-RR) was isolated from F2 screens of field populations in Texas. Characterizing the resistance mechanism in this strain is important for predicting the sustained efficacy of current commercial Bt traits and guiding the development of future transgenic traits. Resistance to insecticidal proteins in Bt traits is commonly associated with reduced toxin binding, with the exception of Vip3Aa resistance being associated to altered proteolytic processing in the insect host gut. Therefore, Vip3Aa protoxin processing was tested by incubation with midgut fluids from CEW-Vip-RR relative to a susceptible strain (CEW-SS). Finding no significant processing differences, alterations in Vip3Aa binding were tested by comparing binding of radiolabeled and biotinylated Vip3Aa toxin to midgut brush border membrane vesicles (BBMV) from CEW-Vip-RR and CEW-SS larvae. Specific Vip3Aa binding to CEW-Vip-RR BBMV in these experiments was consistently reduced when compared with CEW-SS BBMV. These results support that an altered Vip3Aa- receptor is associated with resistance in CEW-Vip-RR. Understanding this resistance mechanism could have important implications for resistance management decisions considering widespread Cry1 and Cry2 resistance in H. zea populations. IMPORTANCEHelicoverpa zea is a major crop pest in the United States that is managed with transgenic corn and cotton producing insecticidal proteins from the bacterium, Bacillus thuringiensis (Bt). However, H. zea has evolved widespread resistance to the Cry proteins produced in Bt corn and cotton, leaving Vip3Aa as the only plant incorporated protectant in Bt crops consistently providing excellent control of H. zea. The benefits provided by Bt crops will be substantially reduced if widespread Vip3Aa resistance develops in H. zea field populations. Therefore, it is important to identify resistance alleles and mechanisms that contribute to Vip3Aa resistance to ensure that informed resistance management strategies are implemented. This study is the first report of reduced binding of Vip3Aa to midgut receptors associated with resistance.

pathology↗

bioRxiv2020

Whole genome comparisons reveal panmixia among fall armyworm (Spodoptera frugiperda) from diverse locations

The fall armyworm (Spodoptera frugiperda (J.E. Smith)) is a highly polyphagous agricultural pest with long-distance migratory behavior threatening food security worldwide. This pest has a host range of >80 plant species, but two host strains are recognized based on their association with corn (C-strain) or rice and smaller grasses (R-strain). In this study, the population structure and genetic diversity in 55 S. frugiperda samples from Argentina, Brazil, Kenya, Puerto Rico and the United States (USA) were surveyed to further our understanding of whole genome nuclear diversity. Comparisons at the genomic level suggest panmixia in this population, other than a minor reduction in gene flow between the two overwintering populations in the continental USA that also corresponded to genetically distinct host strains. Two maternal lines were detected from analysis of mitochondrial genomes. We found members from the Eastern Hemisphere interspersed within both continental USA overwintering subpopulations, suggesting multiple individuals were likely introduced to Africa. Comparisons between laboratory-reared and field collected S. frugiperda support similar genomic diversity, validating the experimental use of laboratory strains. Our research is the largest diverse collection of United States S. frugiperda whole genome sequences characterized to date, covering eight continental states and a USA territory (Puerto Rico). The genomic resources presented provide foundational information to understand gene flow at the whole genome level among S. frugiperda populations.

genomics↗

bioRxiv2020

Reduced levels of membrane-bound alkaline phosphatase in Vip3Aa-resistant Heliothis virescens

The Vip3Aa insecticidal protein from Bacillus thuringiensis (Bt) is produced by specific transgenic corn and cotton varieties for efficient control of target lepidopteran pests. The main threat to this technology is the evolution of resistance in targeted insect pests, thus understanding the mechanistic basis of resistance is crucial to deploy the most appropriate strategies for resistance management. In this work, a laboratory-selected colony of Heliothis virescens (Vip-Sel) highly resistant to the Vip3Aa protein was used to test whether an alteration of membrane receptors in the insect midgut might explain the resistance phenotype. Binding of 125I-labeled Vip3Aa to brush border membrane vesicles (BBMV) from 3rd instar larvae from Vip-Sel was not significantly different from binding in the reference susceptible colony. Interestingly, BBMV from Vip-Sel larvae show dramatically reduced levels of alkaline phosphatase activity, which was further confirmed by a strong down-regulation of the membrane-bound alkaline phosphatase 1 (HvmALP1) gene. However, its involvement as a receptor for the Vip3Aa protein was not supported by ligand blotting and viability assays with insect cells expressing HvmALP1. These data support that reduced alkaline phosphatase, previously observed in insect colonies resistant to Cry proteins from Bt, may also serve as an indirect marker that is not mechanistically involved in resistance to Vip3Aa. IMPORTANCEThe Vip3Aa insecticidal protein remains the only lepidopteran-specific trait in transgenic Bt crops with no cases of field-evolved resistance. While laboratory-selected resistance to Vip3A has been reported elsewhere, the mechanism for resistance is unknown. Results in this work show lack of significant Vip3Aa binding alterations in resistant and reference colonies of H. virescens. These observations are in contrast to most cases of high levels of resistance to insecticidal Bt proteins for which decreased binding is commonly detected. In addition, this study provides the first evidence of down-regulation of membrane bound alkaline phosphatase (mALP) associated with Vip3Aa resistance, a phenomenon commonly associated with resistance to Cry proteins from Bt. Results from this work suggest that mALP down-regulation may be a useful biomarker yet reject its direct participation in resistance to Vip3Aa.

microbiology↗