Biology subjects

Bird, K. A.

Publications and source records attributed to Bird, K. A..

12 recordsLinked to original sources

bioRxiv2026

Gene functional-state covariance reveals modular structure in the Arabidopsis thaliana dispensable genome

Classical multilocus theory predicts that selection acting on combinations of loci can maintain non-random associations among allelic states, causing selection to act on multilocus genotypes rather than individual alleles. Across eukaryotic species, pangenome studies have documented thousands of genes that vary in functional status between individuals, yet this variation is analyzed as if each gene evolves independently. Here we test for non-random association within the dispensable pangenome across 1,012 natural genotypes of Arabidopsis thaliana to better understand the structure and evolution of eukaryotic pangenomes. Genome-wide pairwise association testing of loss-of-function alleles across genotypes identified 150,033 significantly covarying gene pairs among 5,679 unique genes after controlling for kinship and population structure. Most associations were between genes on different chromosomes, and covarying gene pairs showed greater co-expression and functional similarity than expected by chance. Network analysis revealed a non-random higher-order architecture comprising stable functional communities with distinct biological functions and structured connectivity among communities. The enriched functions and connectivity of communities revealed a tight coupling of modules involving plant immunity, environmental response, and specialized metabolism, highlighting how these systems integrate and evolve in response to dynamic ecological pressures. Taken together, these results show that the dispensable genome has a complex higher-order structure driven by functionally interacting genes, and that variation in gene content provides a population-scale resource for investigating the organization and evolution of biological systems.

genomics↗

bioRxiv2026

Landrace and bred accessions of allotetraploid sour cherry (Prunus cerasus L.) reveal variation in subgenome dosage and subgenome expression bias

Subgenome dominance is a phenomenon observed in many allopolyploids where one parental genome exhibits stronger influence over phenotype than the other parental genomes. This may present as preferential retention of one subgenome through fractionation, replacement via homoeologous exchange, or as subgenome expression bias, where one subgenome is expressed at a higher abundance compared to other subgenomes. Sour cherry (Prunus cerasus) is an allotetraploid fruit tree species resulting from an interspecific cross between extant relatives of ground cherry (P. fruticosa) and sweet cherry (P. avium). Prior comparative genomic analyses suggest that the sour cherry cultivar Montmorency contains three subgenomes. Subgenomes A and A, each present in one copy, are derived from a P. fruticosa-like ancestor, and B, present in two copies, is derived from a P. avium-like ancestor. In this study we investigated the subgenome dynamics of the three subgenomes of sour cherry in four diverse landraces and two cultivars, including Montmorency. We found evidence of 26 homoeologous exchange events and five whole-homoeolog replacements relative to Montmorency in three of the six accessions. We also detected subgenome expression bias favoring the A and A subgenomes over the B subgenome, the magnitude of which differs between accessions and changes over the course of fruit development. Lastly, we show differences in dosage variation and expression bias of four previously-described genes in Montmorency associated with fruit softening, a key trait in this crop. These findings on subgenome dominance offer valuable insights into how this phenomenon may influence traits important for sour cherry breeding.

genetics↗

bioRxiv2025

Structure and sequence evolution in the pennycress (Thlaspi arvense) pangenome

O_LIEukaryotic genomes harbor many forms of variation, including nucleotide diversity and structural polymorphisms, which experience natural selection and contribute to genome evolution and biodiversity. However, harnessing this variation for agriculture hinges on our ability to detect, quantify, catalog, and utilize genetic diversity. C_LIO_LIHere, we explore seven complete genomes of the emerging biofuel crop pennycress (Thlaspi arvense) drawn from across the speciess current genetic diversity to catalogue variation in genome structure and content. C_LIO_LIAcross this new pangenome resource, we find contrasting evolutionary modes in different genomic regions. Gene-poor, repeat-rich pericentromeric regions experience frequent rearrangements, including repeated centromere repositioning. In contrast, conserved gene-dense chromosome arms maintain large-scale synteny across accessions, even in fast-evolving immune genes where microsynteny breaks down across species but the macrosynteny of gene cluster positioning is maintained. C_LIO_LIOur findings highlight that multiple elements of the genome experience dynamic evolution that conserves functional content on the chromosome scale but allows rearrangement and presence-absence variation on a local scale. This diversity is invisible to classical reference-based approaches and highlights the strength and utility of pangenomic resources. These results provide a valuable case study of rapid genomic structural evolution within a species and powerful resources for crop development in an emerging biofuel crop. C_LI

genomics↗

bioRxiv2024

The multi-scale complexity of human genetic variation beyond continental groups

Traditional clustering and visualization approaches in human genetics often operate under frameworks that assume inherent, discrete groupings1,2. These methods can inadvertently simplify multifaceted relationships, functioning to entrench the idea of typological groups3. We introduce a network-based pipeline and visualization tool grounded in relational thinking4, which constructs networks from a variety of genetic similarity metrics. We identify communities at multiple resolutions, departing from typological models of analysis and interpretation that categorize individuals into a (predefined) number of sets. We applied our pipeline to a dataset merged from the 1000 Genomes and Human Genome Diversity Project5, revealing the limitations of traditional groupings and capturing the complexities introduced by demographic events and evolutionary processes. This method embraces the context-specificity of genetic similarities that are salient depending on the question, markers of interest, and study individuals. Different numbers of communities are revealed depending on the resolution chosen and metric used, underscoring a fluid spectrum of genetic relationships and challenging the notion of universal categorization. We provide a web application (https://sohail-lab.shinyapps.io/GG-NC/) for interactive visualization and engagement with these intricate genetic landscapes.

genomics↗

bioRxiv2024

Convergent evolution of epigenome recruited DNA repair across the Tree of Life

Mutations fuel evolution while also causing diseases like cancer. Epigenome-targeted DNA repair can help organisms protect important genomic regions from mutation. However, the adaptive value, mechanistic diversity, and evolution of epigenome-targeted DNA repair systems across the tree of life remain unresolved. Here, we investigated the evolution of histone reader domains fused to the DNA repair protein MSH6 (MutS Homolog 6) across over 4,000 eukaryotes. We uncovered a paradigmatic example of convergent evolution: MSH6 has independently acquired distinct histone reader domains; PWWP (metazoa) and Tudor (plants), previously shown to target histone modifications in active genes in humans (H3K36me3) and Arabidopsis (H3K4me1). Conservation in MSH6 histone reader domains shows signatures of natural selection, particularly for amino acids that bind specific histone modifications. Species that have gained or retained MSH6 histone readers tend to have larger genome sizes, especially marked by significantly more introns in genic regions. These patterns support previous theoretical predictions about the co-evolution of genome architectures and mutation rate heterogeneity. The evolution of epigenome-targeted DNA repair has implications for genome evolution, health, and the mutational origins of genetic diversity across the tree of life. Short SummaryFusions between histone reader domains and the mismatch repair protein MSH6 have evolved multiple times across Eukaryotes and show evidence of selection, providing mechanistic and theoretical insight into the forces shaping genomic mutation rate heterogeneity.

evolutionary biology↗

bioRxiv2024

Allopolyploidy expanded gene content but not pangenomic variation in the hexaploid oilseed Camelina sativa

Ancient whole-genome duplications (WGDs) are believed to facilitate novelty and adaptation by providing the raw fuel for new genes. However, it is unclear how recent WGDs may contribute to evolvability within recent polyploids. Hybridization accompanying some WGDs may combine divergent gene content among diploid species. Some theory and evidence suggest that polyploids have a greater accumulation and tolerance of gene presence-absence and genomic structural variation, but it is unclear to what extent either is true. To test how recent polyploidy may influence pangenomic variation, we sequenced, assembled, and annotated twelve complete, chromosome-scale genomes of Camelina sativa, an allohexaploid biofuel crop with three distinct subgenomes. Using pangenomic comparative analyses, we characterized gene presence-absence and genomic structural variation both within and between the subgenomes. We found over 75% of ortholog gene clusters are core in Camelina sativa and <10% of sequence space was affected by genomic structural rearrangements. In contrast, 19% of gene clusters were unique to one subgenome, and the majority of these were Camelina-specific (no ortholog in Arabidopsis). We identified an inversion that may contribute to vernalization requirements in winter-type Camelina, and an enrichment of Camelina-specific genes with enzymatic processes related to seed oil quality and Camelinas unique glucosinolate profile. Genes related to these traits exhibited little presence-absence variation. Our results reveal minimal pangenomic variation in this species, and instead show how hybridization accompanied by WGD may benefit polyploids by merging diverged gene content of different species.

genomics↗

bioRxiv2022

The last missing piece of the Triangle of U: the evolution of the tetraploid Brassica carinata genome

Ethiopian mustard (Brassica carinata) is an ancient crop with significant potential for expanded cultivation as a biodiesel feedstock. The remarkable stress resilience of B. carinata and desirable seed fatty acid profile addresses the ongoing food vs. fuel debate as the crop is productive on marginal lands otherwise not suitable for even closely related species. B. carinata is one of six key Brassica spp. that share three major genomes: three diploid species (AA, BB, CC) that spontaneously hybridized in a pairwise manner, forming three allotetraploid species (AABB, AACC, and BBCC). Each of these genomes has been researched extensively, except for that of B. carinata. In the present study, we report a high-quality, 1.31 Gbp genome with 156.9-fold sequencing coverage for B. carinata var. Gomenzer, completing and confirming the classic Triangle of U, a theory of the evolutionary relationships among these six species that arose almost a century ago. Our assembly provides insights into the genomic features that give rise to B. carinatas superior agronomic traits for developing more climate-resilient Brassica crops with excellent oil production. Notably, we identified an expansion of transcription factor networks and agronomically-important gene families. Completing the Triangle of U comparative genomics platform allowed us to examine the dynamics of polyploid evolution and the role of subgenome dominance in domestication and agronomical improvement.

genetics↗

bioRxiv2021

A genome in flux: homoeologous exchanges, subgenome dominance, and gene dosage balance constraints in resynthesized allopolyploid Brassica napus

The Gene Balance Hypothesis (GBH) proposes that selection acts on the dosage (i.e. copy number) of genes within dosage-sensitive portions of networks, pathways, and protein complexes to maintain balanced stoichiometry of interacting proteins, because perturbations to stoichiometric balance can result in reduced fitness. This selection has been called dosage balance selection. Dosage balance selection is also hypothesized to constrain expression responses to dosage changes, making dosage-sensitive genes (those encoding members of interacting proteins) experience more similar expression changes. In allopolyploids, where whole-genome duplication involves hybridization of diverged lineages, organisms often experience homoeologous exchanges (HEs) that recombine, duplicate, and delete homoeologous regions of the genome and alter the expression of homoeologous gene pairs. Although the GBH makes predictions about the expression response to HEs, they have not been empirically tested. We used genomic and transcriptomic data from six resynthesized, isogenic Brassica napus lines over ten generations to identify HEs, analyzed expression responses, and tested for patterns of genomic imbalance. Groups of dosage-sensitive genes had less variable expression responses to HEs than dosage-insensitive genes, a sign that their relative dosage is constrained. This difference was absent for homoeologous pairs whose expression was biased toward the BnA subgenome. Finally, the expression response to HEs was more variable than the response to WGD, suggesting HEs create genomic imbalance. These findings expand our knowledge of the impact of dosage balance selection on genome evolution and potentially connect patterns in polyploid genomes over time; from homoeolog expression bias to duplicate gene retention.

evolutionary biology↗

bioRxiv2021

Diversification, Spread, and Admixture of Octoploid Strawberry in the Western Hemisphere

Premise of the studyOctoploid strawberry (Fragaria sp.) has a complex evolutionary history that has until recently been intractable due to limitations of available genomic resources. While recent work has further uncovered the evolutionary history of the octoploid strawberry, there are still open questions. Much is still unknown about the evolutionary relationship of the wild octoploid species, Fragaria virginiana and Fragaria chiloensis, and gene flow within and among species after the original formation of the octoploid genome. MethodsWe leveraged a diversity collection of wild octoploid eco-types of strawberry representing the recognized subspecies and ranging from Alaska to Southern Chile, and a high density SNP array to investigate wild octoploid strawberry evolution. Evolutionary relationships are interrogated with phylogenetic analysis and genetic clustering algorithms. Additionally, admixture among and within species is assessed with model-based and tree-based approaches. Key ResultsPhylogenetic analysis revealed that the two octoploid strawberry species are monophyletic sister lineages. The genetic clustering results show substructure between North Americana and South American F. chiloensis populations. Additionally, model-based and tree-based methods support gene flow within and among the two octoploid species, including newly identified admixture in the Hawaiian F. chiloensis subsp. sandwicensis population that appears to be from an ancestral F. chiloensis population. ConclusionF. virginiana and F. chiloensis are supported as monophyletic and sister lineages. All but one of the subspecies recognized within both octoploid species show extensive paraphyly. Furthermore, the phylogenetic relationship among F. chiloensis populations supports a single population range expansion southward from North America. The inter- and intraspecific relationships of octoploid strawberry are complex and suggest substantial and deep gene flow between sympatric populations among and within species.

evolutionary biology↗

bioRxiv2019

Replaying the evolutionary tape to investigate subgenome dominance in allopolyploidBrassica napus

Interspecific hybridization and allopolyploidization merges evolutionarily distinct parental genomes (subgenomes) into a single nucleus. A frequent observation is that one subgenome is "dominant" over the other subgenome, having a greater number of reatined duplicate genes and being more highly expressed. Which subgenome becomes dominantly expressed in allopolyploids remains poorly understood. Here we "replayed the evolutionary tape" with six isogenic resynthesized Brassica napus (rapeseed) allopolyploid lines and investigated subgenome dominance patterns over the first ten generations. We found that the same subgenome was consistently more dominantly expressed in all lines and generations. Furthermore, DNA methylation differences between subgenomes mirrored the observed gene expression bias towards the Brassica oleracea derived C subgenome in all lines and generations. These differences in gene expression and methylation were also found when comparing the progenitor genomes, suggesting subgenome dominance is related to inherited parental genome differences rather than a byproduct of allopolyploidization. Gene network analyses indicated an enrichment for network interactions and several biological functions for C subgenome biased pairs, but no enrichment was observed for A subgenome biased pairs. These findings demonstrate that "replaying the evolutionary tape" in allopolyploids results in repeatable and predictable subgenome expression dominance patterns based on preexisting genetic differences among the parental species. These findings have major implications regarding the genotypic and phenotypic diversity observed following plant hybridization in both ecological and agricultural contexts.

evolutionary biology↗

bioRxiv2019

Disease Resistance Genetics and Genomics in Octoploid Strawberry

Octoploid strawberry (Fragaria x ananassa) is a valuable specialty crop, but profitable production and availability are threatened by many pathogens. Efforts to identify and introgress useful disease resistance genes (R-genes) in breeding programs are complicated by strawberrys complex octoploid genome. Recently-developed resources in strawberry, including a complete octoploid reference genome and high-resolution octoploid genotyping, enable new analyses in strawberry disease resistance genetics. This study characterizes the complete R-gene collection in the genomes of commercial octoploid strawberry and two diploid ancestral relatives, and introduces several new technological and data resources for strawberry disease resistance research. These include octoploid R-gene transcription profiling, dN/dS analysis, eQTL analysis and RenSeq analysis in cultivars. Octoploid fruit transcript expression quantitative trait loci (eQTL) were identified for 77 putative R-genes. R-genes from the ancestral diploids Fragaria vesca and Fragaria iinumae were compared, revealing differential inheritance and retention of various octoploid R-gene subtypes. The mode and magnitude of natural selection of individual F. x ananassa R-genes was also determined via dN/dS analysis. R-gene sequencing using enriched libraries (RenSeq) has been used recently for R-gene discovery in many crops, however this technique somewhat relies upon a priori knowledge of desired sequences. An octoploid strawberry capture-probe panel, derived from the results of this study, is validated in a RenSeq experiment and is presented for community use. These results give unprecedented insight into crop disease resistance genetics, and represent an advance towards exploiting variation for strawberry cultivar improvement.

genomics↗

bioRxiv2018

Subset-based genomic prediction provides insights into the genetic architecture of free amino acid levels in dry Arabidopsis thaliana seeds

Plant growth, development, and nutritional quality depends upon amino acid homeostasis, especially in seeds. However, our understanding of the underlying genetics influencing amino acid content and composition remains limited, with only a few candidate genes and quantitative trait loci identified to date. Improved knowledge of the genetics and biological processes that determine amino acid levels will enable researchers to use this information for plant breeding and biological discovery. Towards this goal, we used genomic prediction to identify biological processes that are associated with, and therefore potentially influence, free amino acid (FAA) composition in seeds of the model plant Arabidopsis thaliana. Markers were split into categories based on metabolic pathway annotations and fit using a genomic partitioning model to evaluate the influence of each pathway on heritability explained, model fit, and predictive ability. Selected pathways included processes known to influence FAA composition, albeit to an unknown degree, and spanned four categories: amino acid, core, specialized, and protein metabolism. Using this approach, we identified associations for pathways containing known variants for FAA traits, in addition to finding new trait-pathway associations. Markers related to amino acid metabolism, which are directly involved in the FAA regulation, improved predictive ability for branched chain amino acids and histidine. The use of genomic partitioning also revealed patterns across biochemical families, in which serine-derived FAAs were associated with protein related annotations and aromatic FAAs were associated with specialized metabolic pathways. Taken together, these findings provide evidence that genomic partitioning is a viable strategy to uncover the relative contributions of biological processes to FAA traits in seeds, offering a promising framework to guide hypothesis testing and narrow the search space for candidate genes.

genetics↗