Biology subjects

Stapley, J.

Publications and source records attributed to Stapley, J..

10 recordsLinked to original sources

bioRxiv2026

Genetic mapping of trait plasticity in a plant pathogenic fungus reveals genetic architecture and candidate genes for plasticity

Understanding how plant pathogens respond to environmental change is needed to better manage plant diseases. Phenotypic plasticity, the ability of a single genotype to produce different phenotypes across different environments, can influence pathogen adaptation and host-pathogen dynamics. Few studies have investigated the mechanisms underlying phenotypic plasticity in plant pathogens. Here we used phenotypic and genotypic data collected over >15 years and across multiple environments to perform genetic mapping of plasticity traits in the wheat pathogen Zymoseptoria tritici. Most (75%) of the QTL for plasticity (plQTL) overlapped with their corresponding mean QTL (mnQTL), suggesting that plasticity is controlled mainly by pleiotropic genes or tightly linked genes. 25% of the plQTL mapped to genomic locations separate from the mnQTL, suggesting that plasticity in these cases results from epistasis between unlinked loci. In several cases plasticity measured across different environmental gradients mapped to the same genomic positions, suggesting a shared control of plasticity for unrelated factors. These cases of shared control could be due to master regulators of plasticity or gene clusters. This mapping study provide unprecedented insights into the genetic architecture of plasticity in fungal plant pathogens.

evolutionary biology↗

bioRxiv2024

Mapping genomic regions associated with temperature stress in the wheat pathogen Zymoseptoria tritici

Climate change can alter interactions between plants and their pathogens, which could adversely affect crop production. To better understand the molecular mechanisms underlying the responses of pathogenic fungal to temperature stress, we conducted a quantitative trait loci (QTL) mapping study in the wheat pathogen Zymoseptoria tritici to identify genomic regions associated with colony growth and melanisation at three temperatures (10{degrees}C, 18{degrees}C, 27{degrees}C). We then identified likely candidate genes for thermal adaptation within these intervals by combining information regarding gene function, GO annotation enrichment, transcriptional profile, and results from previous genome wide association studies (GWAS) investigating responses to climate, temperature and thermal adaptation. The QTL mapping, conducted for two separate crosses involving four Swiss parents, found significant QTL uniquely associated with traits measured in high and low temperatures. These intervals contained many genes known to regulate responses to temperature stress, including heat shock proteins (HSPs) and proteins involved in the mitogen-activated protein kinase (MAPK) pathways, and were enriched for genes with a zinc ion binding GO annotation. We highlight the most promising candidate genes for thermal adaptation, including an ammonium transporter gene, a stress response factor (Whi1) and two MAPK pathway genes - SSk2 and Opy2. Future validation work on these candidate genes could provide novel insight into the molecular mechanisms underlying temperature adaptation in this important wheat pathogen.

genetics↗

bioRxiv2024

Cultivar-specific fungicide resistance emerges during a growing season in field populations of Zymoseptoria tritici

Zymoseptoria tritici causes the most damaging wheat disease in Europe, septoria tritici blotch (STB). In Europe, STB is controlled mainly by fungicides and fungicide resistance is frequently reported. While fungicide resistance is thought to emerge mainly from standing genetic variation within field populations of Z. tritici, few studies have attempted to quantify the degree of fungicide resistance occurring at the field scale and to measure changes in frequencies of resistant strains following fungicide applications during a single growing season. Even fewer studies have considered the effects of different wheat cultivars on the emergence of fungicide resistance. We measured EC50 values for 1005 strains of Z. tritici sampled at two time points from 17 different wheat cultivars growing in a replicated field experiment that was treated with combinations of five different fungicides three times during the growing season. We found that field populations of Z. tritici can maintain a very high diversity in fungicide sensitivity phenotypes despite three fungicide treatments, with as much diversity found within a single field during a single growing season as has been described across all of Europe over several years. Multidrug resistance to two or more fungicides was found in 18.9% of the tested strains. We discovered that wheat cultivars that were more resistant to STB tended to be colonized by Z. tritici strains that exhibited higher fungicide resistance. We also found that specific wheat cultivars selected for resistance to specific active ingredients. Overall, our findings illustrate the many challenges associated with designing fungicide treatment programs that aim to reduce selection for fungicide resistance when confronted with a pathogen like Z. tritici that has a very high evolutionary potential.

microbiology↗

bioRxiv2023

Teaching transposon classification as a means to crowd source the curation of repeat annotation - a tardigrade perspective

The advancement of sequencing technologies results in the rapid release of hundreds of new genome assemblies a year providing unprecedented resources for the study of genome evolution. Within this context, the significance of in-depth analyses of repetitive elements, transposable elements (TEs) in particular, is increasingly recognized in understanding genome evolution. Despite the plethora of available bioinformatic tools for identifying and annotating TEs, the phylogenetic distance of the target species from a curated and classified database of repetitive element sequences constrains any automated annotation effort. Manual curation of raw repeat libraries is deemed essential due to the frequent incompleteness of automatically generated consensus sequences. However, manual curation and classification are time-consuming processes that offer limited short-term academic rewards and are typically confined to a few research groups where methods are taught through hands-on experience. Crowd sourcing efforts could offer a significant opportunity to bridge the gap between learning the methods of curation effectively and empowering the scientific community with high-quality, reusable repeat libraries. Here, we present an example of such crowd sourcing effort developed through both in-person and online courses built around a collaborative peer-reviewed teaching process that can be used as teaching reference guide for similar projects. The collaborative manual curation of TEs from two tardigrade species, for which there were no TE libraries available, resulted in the successful characterization of hundreds of new and diverse TEs: A hidden treasure awaits discovery within non-model organisms.

evolutionary biology↗

bioRxiv2023

Molecular epidemiology of Cercospora leaf spot on resistant and susceptible sugar beet hybrids

Cercospora leaf spot (CLS), caused by Cercospora beticola, is a major foliar disease impacting sugar beet production worldwide. The development of new resistant sugar beet hybrids is a powerful tool to better manage the disease, but it is unclear how these hybrids affect CLS epidemiology. We used a molecular epidemiology approach to study natural epidemics of CLS affecting two susceptible and two resistant sugar beet hybrids at two field sites. Infected plants were geotagged on a weekly basis. Isolations of C. beticola were made from infected leaves and genotyped using six simple sequence repeat loci to identify clones. We determined that CLS epidemics had a later onset in plots planted to resistant hybrids, but once the pathogen established an infection, there was little difference between resistant and susceptible hybrids in the probability of localized spread and dispersal. We found that different clones often infected the same leaf and that clusters of infected plants were often colonized by a mixture of clones. There was little overall difference in genetic diversity between resistant and susceptible hybrids, however genotypic evenness differed at one site. In this site we found one genotype restricted to the resistant cultivars at a high frequency. At the end of the epidemic infections were not randomly distributed across the fields and we found that a single clone could spread over a distance of 100 m during a growing season.

pathology↗

bioRxiv2023

Genome-wide association studies reveal a rapidly evolving candidate avirulence effector in the Cercospora leaf spot pathogen Cercospora beticola

The major resistance gene BvCR4 recently bred into sugar beets provides a high level of resistance to Cercospora leaf spot caused by the fungal pathogen Cercospora beticola. The occurrence of pathogen strains virulent to BvCR4 was studied using field trials in Switzerland. Virulence of a subset of these strains was evaluated in a field trial conducted under elevated artificial disease pressure. We created a new C. bet cola reference genome and mapped whole genome sequences of 256 field-collected isolates. These were combined with virulence phenotypes to conduct three separate GWAS to identify candidate avirulence genes. We identified a locus associated with avirulence containing a single candidate avirulence effector gene named AvrCR4. All virulent isolates either lacked AvrCR4 or had non-synonymous mutations within the gene. AvrCR4 was present in all 74 isolates from non-BvCR4 hybrids, whereas 33 of 89 isolates from BvCR4 hybrids carried a deletion. We also mapped genomic data from 190 publicly available U.S. isolates to our new reference genome. The AvrCR4 deletion was found in only one of 95 unique isolates from non-BvCR4 hybrids in the U.S. AvrCR4 presents a unique example of an avirulence effector in which virulent alleles have only recently emerged. Most likely these were selected out of standing genetic variation after deployment of BvCR4. Identification of AvrCR4 will enable real-time screening of C. beticola populations for the emergence and spread of virulent isolates.

evolutionary biology↗

bioRxiv2023

Genetic diversity and population structure of Epichloe fungal pathogens of plants in natural ecosystems

Understanding the population genetic processes driving the evolution of plant pathogens is of central interest to plant pathologists and evolutionary biologists alike. However, most studies focus on host-pathogen associations in agricultural systems of high genetic and environmental homogeneity and less is known about the genetic structure of pathogen populations infecting wild plants in natural ecosystems. We performed parallel population sampling of two pathogenic Epichloe species occurring sympatrically on different host grasses in natural and seminatural grasslands in Europe: E. typhina infecting Dactylis glomerata and E. clarkii infecting Holcus lanatus. We sequenced 422 haploid isolates and generated genome-wide SNP datasets to investigate genetic diversity and population structure. In both species geographically separated populations formed genetically distinct groups, however population separation was less distinct in E. typhina compared to E. clarkii. The patterns of among population admixture also differed between species across the same geographic range: we found higher levels of population genetic differentiation and a stronger effect of isolation by distance in E. clarkii compared to E. typhina, consistent with lower levels of gene flow in the former. This pattern may be explained by the different dispersal abilities of the two pathogens and is expected to be influenced by the genetic structure of host populations. In addition, genetic diversity was higher in E. typhina populations compared to E. clarkii, indicative of higher effective population size in E. typhina. These results suggest that the effect of genetic drift and the efficacy of selection may differ in the two species. Our study provides evidence of how ecologically similar species occupying the same geographical space can experience different evolutionary contexts, which could influence local adaptation and coevolutionary dynamics of these fungal pathogens.

evolutionary biology↗

bioRxiv2022

Quantitative trait locus mapping of osmotic stress response in the wheat pathogen Zymoseptoria tritici

Osmotic stress is a ubiquitous and potent stress for all living organisms, but few studies have investigated the genetic basis of salt tolerance in filamentous fungi. The main aim of this study was to identify regions of the genome associated with tolerance to potassium chloride in the wheat pathogen Zymoseptoria tritici. A secondary aim was to identify candidate genes affecting salt tolerance within the most promising chromosomal regions. We achieved these aims with a quantitative trait locus (QTL) mapping study using offspring from two crosses grown in vitro in the presence or absence of osmotic stress imposed by 0.75M KCl. We identified significant QTL for most of the traits in both crosses. Several QTL overlapped with QTL identified in earlier studies for other traits and some QTL explained trait variation in both the control and salt stress environments. A significant QTL on chromosome 3 explained variation in colony radius at 8 days post inoculation (dpi) in the KCl environment as well as colony radius KCl tolerance at 8 dpi. The QTL peak had a high LOD and encompassed an interval containing only 36 genes. Six of these genes present promising candidates for functional analyses. A GO enrichment analysis of QTL unique to the KCl environment found evidence for enrichment of functions involved in osmotic stress responses.

genetics↗

bioRxiv2018

Male Anolis lizards prefer virgin females

Males can gain fitness benefits by preferentially courting and mating with virgin females if they represent a lower risk of sperm competition. When females mate multiply, but do not remate frequently, males can experience a lower level of sperm competition when mating with virgins. Male preference for virgins has been demonstrated many times in invertebrates but rarely in vertebrates. In this study, I tested if Anolis apletophallus males preferentially courted virgin females more than non-virgin females, in two-choice trails where the virgin was smaller than the non-virgin, and trails where the females were size-matched. In both trails males preferentially courted the virgin females more than non-virgin females. This suggests males can discriminate between females based on their reproductive history and that they do not use body size as a cue. Males most likely used visual signals from the female, although these signals could not be identified in this study. This is only the second study to show male preference for virgins in vertebrates. Although it is possible that male preference for virgins is relatively rare in vertebrates, I argue that certain life history traits, namely, where large females do not have reproductive benefits, and or when sperm is stored between subsequent reproductive events this preference function can evolve. Future studies focusing on such systems are likely to be fruitful with respect to this male mating preference and may help us to better understand the evolution of male mating preferences and female traits.

animal behavior and cognition↗

bioRxiv2018

Low genetic variation is associated with low mutation rate in the giant duckweed

Mutation rate and effective population size (Ne) jointly determine intraspecific genetic diversity, but the role of mutation rate is often ignored. We investigate genetic diversity, spontaneous mutation rate and Ne in the giant duckweed (Spirodela polyrhiza). Despite its large census population size, whole-genome sequencing of 68 globally sampled individuals revealed extremely low within-species genetic diversity. Assessed under natural conditions, the genome-wide spontaneous mutation rate is at least seven times lower than estimates made for other multicellular eukaryotes, whereas Ne is large. These results demonstrate that low genetic diversity can be associated with large-Ne species, where selection can reduce mutation rates to very low levels, and accurate estimates of mutation rate can help to explain seemingly counterintuitive patterns of genome-wide variation.\n\nOne Sentence SummaryThe low-down on a tiny plant: extremely low genetic diversity in an aquatic plant is associated with its exceptionally low mutation rate.

genetics↗