Biology subjects

Carriere, Y.

Publications and source records attributed to Carriere, Y..

3 recordsLinked to original sources

bioRxiv2021

Novel genetic basis of resistance to Bt toxin Cry1Ac in Helicoverpa zea

Crops genetically engineered to produce insecticidal proteins from the bacterium Bacillus thuringiensis (Bt) have advanced pest management, but their benefits are diminished when pests evolve resistance. Elucidating the genetic basis of pest resistance to Bt toxins can improve resistance monitoring, resistance management, and design of new insecticides. Here, we investigated the genetic basis of resistance to Bt toxin Cry1Ac in the lepidopteran Helicoverpa zea, one of the most damaging crop pests in the United States. To facilitate this research, we built the first chromosome-level genome assembly for this species, which has 31 chromosomes containing 375 Mb and 15,482 predicted proteins. Using a genome-wide association study, fine-scale mapping, and RNA-seq, we identified a 250-kb quantitative trait locus (QTL) on chromosome 13 that was strongly associated with resistance in a strain of H. zea that had been selected for resistance in the field and lab. The mutation in this QTL contributed to but was not sufficient for resistance, which implies alleles in more than one gene contributed to resistance. This QTL contains no genes with a previously reported role in resistance or susceptibility to Bt toxins. However, in resistant insects, this QTL has a premature stop codon in a kinesin gene which is a primary candidate as a mutation contributing to resistance. We found no changes in gene sequence or expression consistently associated with resistance for 11 genes previously implicated in lepidopteran resistance to Cry1Ac. Thus, the results reveal a novel and polygenic basis of resistance.

genetics↗

bioRxiv2019

Mutations in a novel cadherin gene associated with Bt resistance in Helicoverpa zea

Transgenic corn and cotton produce crystalline (Cry) proteins derived from the soil bacterium Bacillus thuringiensis (Bt) that are toxic to lepidopteran larvae. Helicoverpa zea, a key pest of corn and cotton in the U.S., has evolved widespread resistance to these proteins produced in Bt corn and cotton. While the genomic targets of Cry selection and the mutations that produce resistant phenotypes are known in other lepidopteran species, little is known about how Cry proteins shape the genome of H. zea. We scanned the genomes of Cry1Ac-selected and unselected H. zea lines, and identified eleven genes on six scaffolds that showed evidence of selection by Cry1Ac, including cadherin-86C (cad-86C), a gene from a family that is involved in Cry1A resistance in other lepidopterans. Although this gene was expressed in the H. zea larval midgut, the protein it encodes has only 17 to 22% identity with cadherin proteins from other species previously reported to be involved in Bt resistance. An analysis of midgut-expressed cDNAs showed significant between-line differences in the frequencies of putative nonsynonymous substitutions (both SNPs and indels). Our results indicate that cad-86C is a target of Cry1Ac selection in H. zea. Future work should investigate phenotypic effects of these nonsynonymous substitutions and their impact on phenotypic resistance in field populations.

evolutionary biology↗

bioRxiv2018

Vertical transmission of Zika virus from orally infected Aedes aegypti produces infectious adult progeny.

Vertical transmission, or pathogen transfer from mother to offspring, can facilitate persistence of emerging arboviruses, such as Zika virus (ZIKV), in mosquito populations. Understanding vertical transmission and the different environmental and temporal conditions that affect it is important to assess whether new outbreaks could occur without reintroduction of the virus. To determine the rate of vertical transmission for ZIKV, Aedes aegypti females were fed on ZIKV infected blood, maintained under three temperature conditions (27{degrees}C, 30{degrees}C, and 33{degrees}C), and allowed to oviposit three times. Progeny were tested for virus presence at 3, 7, and 14 days after adult emergence. The overall vertical transmission rate was 6.5% (3.9 - 9.9). Vertical transmission was observed across all maternal temperature conditions and was detected in adult progeny as young as 3 days and as late as 14 days post-emergence. In total, 3.4% (1.6 - 6.2) of adult progeny produced saliva with detectable ZIKV, indicating their capacity to transmit ZIKV to humans. To our knowledge, this is the first evidence that vertical transmission occurs from orally-infected female Aedes aegypti to their adult progeny at a range of temperatures, and proof that Zika virus can persist in the saliva of those progeny throughout their lifetimes. These results suggest that the virus may be maintained in Ae. aegypti populations without a vertebrate host, allowing for human infections to occur without consistent re-introductions of ZIKV.\n\nAuthor SummaryIn 2015, Zika virus spread to over 50 countries. However, it is not known whether the virus persisted in the outbreak areas or became locally extinct. One way mosquito-borne viruses, like Zika, could become established is by transferring directly between mosquito generations rather than circulating between mosquitoes and humans. This is known as vertical transmission, and happens when the virus infects the developing eggs of infected maternal mosquitoes. As with other mosquito-borne diseases, like dengue, in order to infect humans the virus must be present in the saliva of infected mosquito progeny during blood feeding. We found vertical transmission occurred throughout the infected mothers reproductive lifetime and across a range of temperature conditions. Vertically infected progeny had Zika virus in their saliva as early as three days after adult emergence, implying that they could infect a person even during their first bloodmeal. Importantly, this work indicates that Zika virus could establish itself in the mosquito population even when human to mosquito transmission is not actively occurring.

epidemiology↗