Biology subjects

Gaude, T.

Publications and source records attributed to Gaude, T..

8 recordsLinked to original sources

bioRxiv2025

Metabolic resistance of the tiger mosquito to pyrethroid insecticides in La Reunion Island likely results from local adaptation

The resistance of mosquitoes to insecticides is a valuable model system for studying the genetic bases of xenobiotic adaptation in insects. The spread of the Asian tiger mosquito Aedes albopictus combined to the massive use of pyrethroid insecticides to limit arbovirus transmission resulted in the rise of resistance in various continents. Here, we investigated the genetic mechanisms underlying the recent adaptation of this mosquito to deltamethrin in La Reunion island. Bioassays confirmed the presence of resistance alleles in field populations. The resistance phenotype was further enhanced in the laboratory following a few generations of controlled selection. Combining whole genome Pool-seq and RNA-seq revealed no evidence of target-site resistance mutations but the over-expression and variant selection of detoxification enzymes associated with pyrethroid metabolism including cytochrome P450s, transferases and ABC-transporters. Among over-expressed detoxification genes, only one was linked to a gene duplication while polymorphism data suggest most of them being trans-regulated. Genome-wide selection signatures revealed a 9 Mb inverted superlocus responding to insecticide selection whose phenotypical importance remains uncertain. Altogether, this study indicates that the multigenic metabolic resistance phenotype observed in this insular territory mainly results from local adaptation. From an applied perspective, this study provides a set of markers to track pyrethroid resistance in the tiger mosquito in the South-West Indian Ocean. As this region is subjected to recurrent arbovirus outbreaks, the additive resistance phenotype that may arise from the introduction of Kdr mutations from other territories also calls for improving resistance surveillance at the regional scale. Author summaryWhile novel vector control strategies are being developed, chemical insecticides remain widely used to control mosquitoes transmitting human diseases such as the Asian tiger mosquito. However, the recurrent use of insecticides resulted in the emergence of resistance which can ultimately affect vector control efficacy. Here, we investigate the genetic bases underlying the resistance of the Asian tiger mosquito to the pyrethroid insecticide deltamethrin in La Reunion island. By combining two complementary genomic approaches, we showed that resistance is mainly caused by an increased insecticide detoxification while classical Knock down resistance mutations affecting the target of the insecticide were not detected. We also showed that resistance is underlain by multiple genetic changes spread across the genome, supporting the local selection of resistance rather than the introduction of resistance alleles. Furthermore, we identified a large inverted supergene responding to insecticide selection. This study provides valuable insights into the genetic bases of insecticide resistance, enabling the implementation of molecular makers to improve the tracking of insecticide resistance in this major mosquito vector across the Indian Ocean.

genomics↗

bioRxiv2024

A genomic duplication spanning multiple P450s contributes to insecticide resistance in the dengue mosquito Aedes aegypti

Resistance of mosquitoes to insecticides is one example of rapid adaptation to anthropogenic selection pressures having a strong impact on human health and activities. Target-site modification and increased insecticide detoxification are the two main mechanisms underlying insecticide resistance in mosquitoes. While target-sites mutations are well characterised and often used to track resistance in the field, the genomic events associated with insecticide detoxification remain partially characterised. Recent studies evidenced the key role of gene duplications in the over-expression of detoxification enzymes and their potential use to track metabolic resistance alleles in the field. However, such genomic events remain difficult to characterise due to their complex genomic architecture and their co-occurrence with other resistance alleles. In this concern, the present work investigated the role of a large genomic duplication affecting a cluster of detoxification enzymes in conferring resistance to the pyrethroid insecticide deltamethrin in the mosquito Aedes aegypti. Two isofemale lines originating from French Guiana and being deprived from major target-site mutations showed distinct insecticide resistance levels. Combining RNA-seq and whole genome pool-seq identified a 220 Kb genomic duplication enhancing the expression of multiple contiguous cytochrome P450s in the resistant line. The genomic architecture of the duplicated loci was elucidated through long read sequencing, evidencing its transposon-mediated evolutionary origin. The involvement of this P450 duplication in deltamethrin survival was supported by a significant phenotypic response to the P450 inhibitor piperonyl butoxide together with genotype-phenotype association and RNA interference. Experimental evolution suggested that this P450 duplication is associated with a significant fitness cost, potentially affecting its adaptive value in presence of other resistance alleles. Overall, this study supports the importance of genomic duplications affecting detoxification enzymes in the rapid adaptation of mosquitoes to insecticides. Deciphering their genomic architecture provides new insights into the evolutionary processes underlying such rapid adaptation. Such findings provide new tools for the surveillance and management of resistance in the field.

evolutionary biology↗

bioRxiv2023

Invasion of the stigma by the pollen tube or an oomycete pathogen: striking similarities and differences

The epidermis is the first barrier that protects organisms from surrounding stresses. Similar to the hyphae of filamentous pathogens that penetrate and invade the outer tissues of the host, the pollen germinates and grows a tube within epidermal cells of the stigma. Early responses of the epidermal layer are therefore decisive for the outcome of these two-cell interaction processes. Here, we aim at characterizing and comparing how the papillae of the stigma respond to intrusion attempts, either by hypha of the hemibiotrophic oomycete root pathogen, Phytophthora parasitica or by the pollen tube. We found that P. parasitica spores attach to the papillae and hyphae subsequently invade the entire pistil. Using transmission electron microscopy, we examined in detail the invasive growth characteristics of P. parasitica and found that the hypha passed through the stigmatic cell wall to grow in contact with the plasma membrane, contrary to the pollen tube that advanced engulfed within the two cell wall layers of the papilla. Further quantitative image analysis revealed that the pathogen and the pollen tube trigger reorganization of the endomembrane system (trans Golgi network, late endosome) and the actin cytoskeleton. Some of these remodeling processes are common to both invaders, while others appear to be more specific showing that the stigmatic cells trigger an appropriate response to the invading structure and somehow can recognize the invader that attempts to penetrate.

plant biology↗

bioRxiv2020

A novel assay for tracking carboxylesterase gene amplifications conferring organophosphate resistance in the mosquito Aedes aegypti: from experimental evolution to field application

By altering gene expression and creating paralogs, genomic amplifications represent a key component of short-term adaptive processes. In insects, the use of insecticides can select gene amplifications causing an increased expression of detoxification enzymes, supporting the usefulness of these DNA markers for monitoring the dynamics of resistance alleles in the field. In this context, the present study aims to characterise a genomic amplification event associated with resistance to organophosphate insecticides in the mosquito Aedes aegypti and to develop a molecular assay to monitor the associated resistance alleles in the field. An experimental evolution experiment using a composite population from Laos supported the association between the over-transcription of multiple contiguous carboxylesterase genes on chromosome 2 and resistance to multiple organophosphate insecticides. Combining whole genome sequencing and qPCR on specific genes confirmed the presence of a ~100 Kb amplification spanning at least five carboxylesterase genes at this locus with the co-existence of multiple structural duplication haplotypes. Field data confirmed their circulation in South-East Asia and revealed high copy number polymorphism among and within populations suggesting a trade-off between this resistance mechanism and associated fitness costs. A dual-colour multiplex TaqMan assay allowing the rapid detection and copy number quantification of this amplification event in Ae. aegypti was developed and validated on field populations. The routine use of this novel assay will improve the tracking of resistance alleles in this major arbovirus vector.

evolutionary biology↗

bioRxiv2019

Dissection of the early pollen-stigma interactions by live-cell imaging

Early events occurring at the surface of the female organ are critical for plant reproduction, especially in species with a dry stigma. Following landing on the stigmatic papilla cells, the pollen hydrates and germinates a tube, which penetrates the cell wall and grows towards the ovules to convey the male gametes to the embryo sac. In self-incompatible (SI) species within the Brassicaceae, these processes are blocked when the stigma encounters an incompatible pollen. Here, based on the generation of SI-Arabidopsis lines and by setting up a live imaging system, we showed that control of pollen hydration has a central role in pollen selectivity. The faster pollen pumps water from the papilla during an initial period of 10 minutes, the faster it germinates. Furthermore, we found that the SI barriers act to block the proper hydration of incompatible pollen and when hydration is promoted by high humidity, an additional control prevents pollen tube penetration into the stigmatic wall. In papilla cells, actin bundles focalize at the contact site with the compatible pollen but not with the incompatible one, raising the possibility that stigmatic cells react to the mechanical pressure applied by the invading growing tube. HighlightA live imaging system coupled with self-incompatible Arabidopsis lines highlight the role of stigmatic cells in controlling pollen hydration and in reacting to pollen tube intrusion by remodeling actin cytoskeleton.

plant biology↗

bioRxiv2019

Combining genetic crosses and pool targeted DNA-seq for untangling genomic variations associated with resistance to multiple insecticides in the dengue vector Aedes aegypti

In addition to combating vector-borne diseases, studying the adaptation of mosquitoes to insecticides provides a remarkable example of evolution-in-action driving the selection of complex phenotypes. Indeed, most resistant mosquito populations show multi-resistance phenotypes as a consequence of the variety of insecticides employed and of the complexity of selected resistance mechanisms. Such complexity makes challenging the identification of alleles conferring resistance to specific insecticides and prevents the development of molecular assays to track them in the field. Here we showed that combining simple genetic crosses with pool targeted DNA-seq can enhance the specificity of resistance alleles detection while maintaining experimental work and sequencing effort at reasonable levels. A multi-resistant population of the mosquito Aedes aegypti was exposed to three distinct insecticides (deltamethrin, bendiocarb and fenitrothion) and survivors to each insecticide were crossed with a susceptible strain to generate 3 distinct lines. F2 individuals from each line were then segregated with 2 insecticide doses. Bioassays supported the improved segregation of resistance alleles between lines. Hundreds of genes covering all detoxifying enzymes and insecticide targets together with more than 7,000 intergenic regions equally spread over mosquito genome were sequenced from pools of F0 and F2 individuals unexposed or surviving insecticide. Differential coverage analysis identified 39 detoxification enzymes showing an increased gene copy number in association with resistance. Combining an allele frequency filtering approach with a Bayesian FST-based genome scan identified multiple genomic regions showing strong selection signatures together with 50 non-synonymous variations associated with resistance. This study provides a simple and cost-effective approach to improve the segregation of resistant alleles in multi-resistant populations while reducing false positives frequently arising when comparing populations showing divergent genetic backgrounds. The identification of these insecticide resistance markers paves the way for the design of novel DNA-based resistance tracking assays.\n\nAuthor summaryIn addition to combating vector-borne diseases, understanding how mosquitoes adapt to insecticides provides a remarkable example of evolution-in-action. However, the variety of insecticides used and the complexity of adaptive mechanisms make it difficult to identify the genetic changes conferring resistance to each insecticide. Here we combined simple controlled crosses with mass DNA sequencing for enhancing the specificity of resistance gene detection. A multi-resistant mosquito population was exposed to three distinct insecticides and survivors were crossed with a susceptible strain to generate 3 distinct mosquito lines. Individuals from the second generation of each line were then segregated based on their resistance to each insecticide. Bioassays supported the improved segregation of genetic resistance markers between lines. Hundreds of genes potentially involved in resistance together with thousands non-genic regions equally spread over mosquito genome were sequenced from individuals from each line. Genomic analyses identified detoxification enzymes showing an increased gene copy number in association with resistance and multiple genomic regions showing strong selection signatures and carrying point mutations associated with resistance. Such approach improves the specificity of resistance gene detection in field mosquito populations resisting to multiple insecticides and paves the way for the design of novel DNA-based resistance tracking tools.

genomics↗

bioRxiv2018

KATANIN-dependent mechanical properties of the stigmatic cell wall regulate pollen tube pathfinding

Successful fertilization in angiosperms depends on the proper trajectory of pollen tubes through the pistil tissues to reach the ovules. Pollen tubes first grow within the cell wall of the papilla cells, applying pressure to the cell. Mechanical forces are known to play a major role in plant cell shape by controlling the orientation of cortical microtubules (CMTs), which in turn mediate deposition of cellulose microfibrils (CMFs). Here, by combining cell imaging and genetic approaches, we show that isotropic reorientation of CMTs and CMFs in aged and katanin1-5 (ktn1-5) papilla cells is accompanied by a tendency of pollen tubes to coil around the papillae. Furthermore, we uncover that aged and ktn1-5 papilla cells have a softer cell wall and provide less resistance to pollen tube growth. Our results reveal an unexpected role for KTN1 in pollen tube guidance by ensuring mechanical anisotropy of the papilla cell wall.

plant biology↗

bioRxiv2018

The molecular signatures of compatible and incompatible pollination

Fertilization in flowering plants depends on the early contact and recognition of pollen grains by the receptive papilla cells of the stigma. To identify the associated molecular pathways, we developed a transcriptomic analysis based on single nucleotide polymorphisms (SNPs) present in two Arabidopsis thaliana accessions, one used as female and the other as male. We succeeded in distinguishing 80 % of transcripts according to their parental origins and drew up a catalog of genes whose expression is modified after pollen-stigma interaction. Global analysis of our data reveals that pattern-triggered immunity (PTI)-associated transcripts are upregulated after compatible pollination. From our analysis, we predicted the activation of the Mitogen-activated Protein Kinase 3 on the female side after compatible pollination, which we confirmed through expression and mutant analysis. Our work defines the molecular signatures of compatible and incompatible pollination, highlights the active status of incompatible stigmas, and unravels a new MPK3-dependent cell wall feature associated with stigma-pollen interaction.

plant biology↗