Biology subjects

Schmitz, R. J.

Publications and source records attributed to Schmitz, R. J..

At least 19 recordsLinked to original sources

bioRxiv2026

Spatially resolved transcriptomics of poplar reveals tissue organization across shoot-associated organs

Poplar (Populus spp.) is a model for tree biology and a platform for engineering woody biomass, biofuels, biomaterials, and bioproducts. Many relevant traits depend on tissue position, developmental stage, and cell type, yet these spatial relationships are difficult to recover from bulk or single-cell transcriptomes. Here, we generated a spatial transcriptome atlas of Populus tremula x P. alba INRA 717-1B4 across the shoot apex, axillary bud, stem, and petiole. After quality control, the atlas retained 29,687 spatial spots from 45 tissue sections and detected 58,748 genes. Histology-guided clustering and marker analysis resolved meristematic, epidermal, cortical, vascular, and organ-specific domains. Cross-organ comparisons assessed whether published markers retained tissue-associated expression across different anatomical contexts and developmental stages, while de novo analysis identified additional domain-enriched candidates. As case studies of the utility of the atlas, we examined the emergence of trichome-associated programs in the shoot apex and adaxial - abaxial expression differences in petioles. A trichome identity score based on poplar markers from the single-cell shoot atlas peaked along the inferred meristem-to-primordium trajectory, revealing spatially localized expression of trichome-associated programs during early leaf development. Petiole expression differences were concentrated in the epidermis and cortex and involved polarity-associated, auxin-responsive, and cell-wall-remodeling genes, with distinct expression profiles across leaf positions. Together, these data provide a spatial reference for investigating tissue differentiation and developmental patterning in a transformable poplar genotype.

plant biology↗

bioRxiv2026

Multimodal single cell analysis reveals a link between flowering and leaf initiation

Zea mays (maize) flowering time is genetically determined and a critical yield determinant. Yet mechanistic understanding of maize flowering remains poor. Indeterminate1 (Id1), a zinc-finger transcription factor (TF), is a monocot-conserved master regulator of maize flowering. Epistasis between Id1 and the ZeaCentroradialis-Delayed Flowering1 (Zcn-Dlf1) inductive pathway partly explains ID1 floral control; however, the strong mutant id1- floral delay is not explained by this pathway alone. To better characterize Id1 actions, we performed single-cell assay for transposase-accessible chromatin and single nucleus RNA sequencing (scATAC-seq and snRNA-seq) comparing Id1+ and id1- developing leaves. These analyses reveal id1- chromatin remodeling via TEOSINTE BRANCHED1 CYCLOIDEA PROLIFERATING CELL FACTOR (TCP) and APETALA2/ETHYLENE RESPONSEFACTOR (AP2/ERF) transcription factors and provide candidate direct targets that include AP2/ERF genes. These candidate direct targets include the family of {beta}-glucosidase genes that lose expression in id1-. Unexpectedly, CRISPR/Cas9 {beta}-glucosidase edits produced plants that phenocopied terminal ear1- (te1-) mutants. This phenocopy prompted an investigation into the genetic relationship between id1-, te1- and flowering. Surprisingly, id1- te1- plants exhibited a synergistic floral delay, producing ~90 leaves before inflorescence production. Beyond highlighting hitherto unappreciated Te1 autonomous flowering roles, this genetic synergy raises the hypothesis that meristem leaf primordia cessation underpins maize flowering.

plant biology↗

bioRxiv2026

Mutational consequences of perturbing DNA repair and chromatin state in Arabidopsis

Mutation rate varies throughout an organisms genome and correlates with many factors, including primary sequence, DNA methylation, gene content, chromatin accessibility, replication timing, and more. Prior work has shown that DNA repair pathways contribute to this variation by repairing certain regions more efficiently than others, sometimes through interactions with gene-associated histone modifications. However, little is known about the relative importance of different DNA repair pathways in shaping intragenomic variability in mutation rate, nor the mutational consequences of perturbing chromatin state. Here, we quantify somatic mutation rate in several DNA repair and chromatin-related Arabidopsis mutants using nanorate sequencing. We find that NER and MMR prevent a smaller fraction of mutations in transposable elements (TEs) compared to other regions of the genome, indicating these pathways are less efficient in heterochromatin. MMR appears to be more efficient in accessible chromatin regions, as its loss nearly abolishes the reduced mutation rate there. TC-NER is the only pathway with greater efficiency in genes than in non-genic non-TE regions, suggesting only TC-NER specifically targets genes. We assay six mutants for histone modifications/variants, but only one (h2a.w.7) displays an altered mutation rate. Instead, mutation rate is elevated in the chromatin remodeler mutant ddm1 and two RNA-directed DNA methylation (RdDM) mutants. The RdDM mutants have a doubled overall mutation rate, but this increase is not localized to RdDM target regions, implicating a transcriptional change, genomic instability, or a secondary function in DNA repair.

genomics↗

bioRxiv2026

Genetic and epigenetic divergence among Arabidopsis thaliana Col-0 laboratory lineages since the 1950s

The model plant Arabidopsis thaliana has been a workhorse of plant biology since the 1950s, when the Columbia-0 (Col-0) accession was widely adopted by the research community as a reference genotype. Since then, Col-0 seeds have been shared among laboratories worldwide and propagated independently, creating a network of related laboratory lineages. Here, we sequenced the genomes and DNA methylomes of 78 Col-0 strains from laboratories and stock centers around the world to assess the genetic and epigenetic variation accumulated during this period and to reconstruct their propagation history from de novo variants. After quality filtering, we identified 1,415 single-nucleotide polymorphisms and 169,677 epimutations across 75 Col-0 lines and used these variants to generate SNP- and epimutation-based phylogenies. The two phylogenies showed highly concordant topologies, but the epimutation-based tree provided greater resolution of relationships among closely related lineages. Divergence-time estimates suggest that many lines have been propagated for approximately one generation per year over several decades, resulting in pairwise divergences of up to approximately 100 generations. We further identified 170 nonsynonymous substitutions and more than 200 candidate epialleles, some of which were associated with gene-expression differences among Col-0 clades and may therefore have functional consequences. Together, these findings show that Col-0 is best viewed not as a single invariant reference genotype, but as a collection of related laboratory lineages that have accumulated genetic, epigenetic, and transcriptional divergence through time, with potential consequences for the reproducibility of experiments across laboratories. Significance StatementThe Arabidopsis Col-0 reference accession is often treated as a single, invariant genotype, yet independently maintained laboratory stocks have accumulated substantial genetic, epigenetic, and transcriptional divergence since the 1950s. Some lineages are separated by more than 100 generations of independent propagation. Mutations and CG epimutations reconstruct nearly identical lineage histories, demonstrating that heritable DNA methylation changes provide a robust record of recent laboratory evolution.

genetics↗

bioRxiv2026

Sequence-based modeling of plant epigenomes reveals cell-type-specific cis-regulatory grammar

How cis-regulatory sequences and their genetic variation govern chromatin accessibility and gene expression to establish plant cell identities remains incompletely understood, despite their fundamental roles in development, environmental responses, and phenotypic diversity. Here we present PEAgent, a framework for training, evaluating and interpreting deep-learning models that predict single-cell chromatin accessibility directly from DNA sequence, packaged in an interactive web portal and toolkit. Models were trained on single-cell chromatin-accessibility atlases of soybean, maize and rice, together spanning over 355,000 cells and 320 cell types and [~]150 million years of evolution. We unraveled a lexicon of 243 cell-type-resolved regulatory patterns, half of them composite, with TCP and bHLH showing the greatest influence and strongest conservation across species. Co-occurrence and in silico synergy analyses, explicitly modeling motif orientation and spacing, revealed two distinct cooperative modes acting at short and nucleosome-scale distances. We further showed that model predictions distinguish grass-conserved from rice-specific regulatory sequences far more accurately than sequence conservation scores alone, and validated the models predicted variant effects against cell-type-level chromatin accessible QTLs. PEAgent provides a foundational resource for decoding cell-type-specific plant cis-regulatory logic and interpreting noncoding variation in plants. HighlightsO_LIPEAgent predicts single-cell chromatin accessibility directly from DNA sequence in soybean, rice and maize. C_LIO_LINearly half of cell-type-resolved patterns are composite, with TCP and bHLH motifs most influential and conserved across species. C_LIO_LICo-occurrence and synergy analysis reveals distinct cooperative grammar at short and nucleosome-scale distances. C_LIO_LIPEAgent distinguishes grass-conserved from lineage-specific regulatory sequences better than sequence conservation scores alone. C_LI

genetics↗

bioRxiv2026

Easy-Multiome enables joint profiling of gene expression and chromatin accessibility in single cells

Gene expression and chromatin accessibility provide complementary insights into the regulatory mechanisms that define cell states. Although methods for jointly profiling these modalities exist, plant applications remain limited because of complex workflows, inconsistent performance, and prohibitive costs. Here, we present easy-Multiome, a streamlined single-cell multiomic workflow that integrates a single in situ reverse transcription step into the standard droplet-based scATAC-seq protocol. Using easy-Multiome, we profiled more than 20,000 nuclei from maize seedlings generating paired gene expression and chromatin accessibility data, with approximately 90% of nuclei containing both high-quality RNA and chromatin accessibility profiles. The resulting transcriptome data resolved 16 clusters corresponding to nine major maize seedling cell types and enabled direct characterization of cell-type-specific chromatin accessibility from the same nuclei. Furthermore, easy-Multiome simultaneously captured cell-type-specific transcription factor expression and the accessibility of their cognate DNA-binding motifs, providing direct links between transcriptional programs and regulatory landscapes. Together, these results demonstrate that easy-Multiome enables robust and efficient joint profiling of plant gene expression and chromatin accessibility while requiring only minimal modifications to existing droplet-based scATAC-seq workflows.

genomics↗

bioRxiv2026

CASCADE recovers promoter-associated regulatory motifs from cell-type-resolved DNA language-model attributions

Gene expression is governed by regulatory DNA and their associated trans factors acting in specific cell types, yet the sequences underlying this control remain poorly mapped in plants. Genome-pretrained DNA language models provide a route to interrogate regulatory sequence directly, but their attributions have largely been interpreted using bulk or whole-tissue data, and standard attribution pipelines can preferentially highlight sequences downstream of the transcription start (TSS) site rather than promoter-associated signals. Here, we train a celltype-resolved sequence-to-expression model from a single-cell soybean (Glycine max) atlas by coupling a soybean-adapted Genomic Pre-trained Network (GPN) to a shared sequence encoder with 66 cell-type-specific output heads. Across 38,339 protein-coding genes, the model achieves a mean per-cell-type, across-gene Pearson correlation of 0.683 and, recast as a highversus-low expression classification, reaches an area under the ROC curve of 0.92 to 0.97 across tissues, at or above dedicated plant sequence models. We then introduce ContextAware Significance of Cross-gene Attribution for Discovering Elements (CASCADE), a positionspecific statistical framework for identifying model-derived candidate regulatory elements from in silico saturation mutagenesis. Relative to the pooled null used by TF-MoDISco, CASCADE shifts motif recovery from downstream of the transcription start site toward promoter sequence, with 77% of CASCADE-exclusive motifs, compared with 12% of TF-MoDISco-exclusive motifs, falling within the promoter. Applied across the atlas, CASCADE identifies approximately 1.39 million candidate elements spanning broadly active, tissue-restricted and cell-type-restricted classes. Together, these analyses establish a position-aware approach for extracting promoterassociated regulatory hypotheses from sequence models and generate a cell-type-resolved map of candidate cis-regulatory elements.

plant biology↗

bioRxiv2026

Time-dependent transcriptomic changes following protoplast isolation in plants

Protoplast isolation is widely used for plant functional genomics and single-cell analyses, but its impact on transcriptional and cell state dynamics remains incompletely understood. Here, we generated time-course RNA-seq data from leaf protoplasts of Arabidopsis, maize, and poplar, sampling at multiple time points following isolation, to systematically characterize global transcriptional dynamics across species. We identified two major drivers of transcriptional variation: a persistent protoplast isolation effect and a progressive time-dependent transcriptional program, which can be divided into early, middle, and late stages corresponding to an immediate stress response, metabolic and chromatin regulation dynamics, and sustained metabolic and proteostasis regulation, together with species-specific differences across stages. We observed a rapid loss of cell-type-specific transcriptional signatures within 6 hours in Arabidopsis and maize, whereas poplar showed a slower decline. Single-nucleus RNA-seq at 6 hours in maize confirmed attenuation of cell-type-specific transcriptional structure. Furthermore, leveraging this time-course dataset enables the identification of aberrant cell states in single-cell RNA-seq data, exemplified by clusters showing elevated activity of protoplast isolation-associated, middle-, and late-stage transcriptional programs characteristic of stress-like states. Together, our results provide a cross-species framework for dissecting protoplast-induced transcriptional and cell state dynamics and facilitate the systematic identification of stress-associated cell states in single-cell transcriptomic data.

plant biology↗

bioRxiv2026

A Comprehensive Epidermal Map from a Poplar Single-Cell Shoot Atlas Reveals New Trichome-Specific Genes

Poplar (Populus spp.) is a model system for tree biology. Specifically, P. tremula x P. alba INRA 717-1B4 (hereafter "poplar 717") has become an important platform for functional genomics and synthetic biology due to its rapid growth and ease of transgenesis. Here, we present a single-cell RNA-seq atlas of the poplar 717 shoot, including apical meristem, primary and secondary stems, and three stages of leaf development. Analysis of ca. 159,000 cells resolved 40 transcriptionally distinct clusters representing 7 major cell types, providing a high-resolution view of shoot development and tissue organization. We focused on the epidermis which constituted >15% of cells in the shoot atlas for in-depth characterization of epidermal heterogeneity. By integrating known marker genes with transcriptomic signatures consistent with established poplar leaf phytochemistry, we annotated epidermal cell subclusters corresponding to developmental stages, spatial location, and specialized cell types, including a distinct population of non-glandular trichomes. Coupling the single-cell RNA-seq atlas with bulk transcriptome data from glabrous mutants enabled the identification of novel trichome markers. Experimental validation of a representative trichome-specific promoter established a tool with potential to support cell type-targeted-metabolic engineering. We provide the poplar 717 atlas to the community through the BioPoplar Atlas Viewer (http://bio-poplar-atlas.com), providing a platform to explore the poplar transcriptome at single-cell resolution and a foundation for data-driven cell type-aware genetic engineering strategies in poplar.

plant biology↗

bioRxiv2025

Lineage-specific evolution of regulatory landscapes in polyploid plant and its diploid progenitors

Cis-regulatory elements are specific DNA sequences that control gene expression in a spatiotemporal manner, and variation within these elements represents a major source of phenotypic diversity and evolutionary innovation. Nevertheless, how regulatory elements evolve and shape gene expression remains poorly understood, particularly in plants. The well-resolved phylogeny of allopolyploid peanut (Arachis hypogaea) and its diploid progenitors, A. duranensis and A. ipaensis, provides an ideal system to investigate the regulatory evolution at a lineage-specific level. By integrating comparative analyses of sequence similarity, chromatin accessibility, histone modifications, conserved noncoding sequences (CNSs), and gene expression, we reconstructed the evolutionary trajectories of Accessible Chromatin Regions (ACRs), where regulatory elements typically reside, and revealed their distinct contributions to homeolog expression bias, unequal expressions between homeologs. Most ACRs exhibited high sequence similarity, comparable chromatin accessibility, and conserved states for H3K4me3, H3K56ac, and H3K36me3, indicating regulatory stability after hybridization and polyploidization. However, a subset of novel ACRs emerged de novo from previously non-regulatory regions or through sequence mutations in preexisting ACRs, arising at different rates and evolutionary stages. Notably, even highly sequence-conserved ACRs exhibited substantial variation in chromatin accessibility, consistent with CNS composition differences and minor sequence variation, although causal relationships remain to be demonstrated. Our analyses further revealed a complex spectrum of CNS dynamics across the diploid-polyploid framework. Overall, our study provides empirical insights into the fine-scale evolution of plant regulatory landscapes and complements previous large-scale comparisons across distant lineages.

evolutionary biology↗

bioRxiv2025

Single-cell multi-omic characterization of the soybean root response to cyst nematode infection

Soybean cyst nematodes parasitize soybean roots by inducing the formation of multinucleate syncytia to feed and complete their life cycle. However, the molecular basis of syncytia initiation and development remains limited. Here, we generated an integrated single-nucleus RNA and chromatin accessibility profile of soybean roots from infected and uninfected plants. We profiled 56,448 high-quality nuclei and identified all major root cell types, including distinct subpopulations enriched with syncytial nuclei. Transcriptomic and chromatin accessibility analyses support their procambium cell signature that progresses through distinct stages associated with immune suppression, cell fusion, and endoreduplication. Integrative gene expression and transcription factor motif chromatin accessibility analyses identified CAMTA1, as a potential transcriptional repressor of defense-related genes including receptor-like kinases, whereas MYB, MYB-related, and E2F were identified as potential transcriptional activators that coordinate cell wall remodeling, chromatin modification and DNA replication, respectively, across developmental trajectories. These findings provide mechanistic insights into host reprogramming during nematode parasitism and serve as a foundational resource for engineering nematode-resistant soybean.

plant biology↗

bioRxiv2025

Hybrids reveal accessible chromatin trans genetic associations

Crosses between genetically distant Zea mays (Maize) inbreds cause hybrid vigour (heterosis): an over-dominant increase in vegetative growth and grain yield. Although the contributing loci are unknown, heterosis strength varies polygenically, with crosses between stiff stalk and non-stiff stalk lineages often producing the highly heterotic F1 seed used for agriculture. As F1 genomes conserve the parental cis-regulatory state, F1 trans-interactions between haplotypes underpin F1 trait over-dominance and heterotic gene expression. Gene expression relies upon transcription factors binding cis-regulatory elements in accessible chromatin regions (ACRs) and recruiting RNA POLYMERASE II. Here, assay for transposase accessible chromatin sequencing (ATAC-seq) examined cis-regulatory element chromatin accessibility inheritance in three different F1 parent-offspring pairs, including a representative stiff stalk-by-non-stiff stalk (B73xOh43) cross. Using concatenated reference alignment, we categorized ACR modes of inheritance (additive, dominant, under/over-dominant), revealing that ACRs are largely inherited additively, and, concordantly, that chromatin accessibility has strong narrow-sense heritability. However, mirroring other heterotic phenotypes, the B73xOh43 cross exhibited the most dominant and over-dominant inheritance. Comparing allele-specific parent-to-offspring chromatin accessibility, we identified F1 differentially trans-regulated ACRs. Using a matched chromatin accessible diversity panel, we found B73xOh43 SNPs with more ACR trans-associations than expected due to chance. These trans-regulatory variants revealed how cell-division and anabolism are elevated in heterotic F1 seedlings. This multiple discovery filtering (MDF) approach to trans-regulatory variant detection is genomic modality agnostic and stands to empower trans-relationship dissection in diverse genetic models.

genetics↗

bioRxiv2025

Mapping genetic modifiers of epimutation rates reveals a punctuated-equilibrium model of CG methylome evolution

Spontaneous epimutations--stochastic changes in cytosine methylation--can persist across generations in plants and are thought to contribute to phenotypic variation. Although epimutations are increasingly studied for their potential long-term effects, it remains unclear why their accumulation varies across genotypes. Here, we tracked DNA methylation across ten generations in [~]400 mutation accumulation lineages derived from [~]70 Arabidopsis Ler x Cvi recombinant inbred lines. Treating epimutation rates as quantitative molecular traits, we mapped a major QTL to a Cvi-derived deletion near VIM2 and VIM4, two genes involved in CG methylation (mCG) maintenance. We show that this deletion rapidly reduces genome-wide methylation to a lower steady-state and compromises mCG maintenance fidelity across generations, resulting in a [~]1.5-fold increase in epimutation rates. Genotypes with elevated rates exhibited accelerated epigenetic drift and phenotypic divergence. Our findings support a punctuated-equilibrium model of mCG evolution, in which sudden disruptions to methylation homeostasis can destabilize epigenetic inheritance over longer time-scales.

genetics↗

bioRxiv2025

Major effect mutations drive DNA methylation variation after colonization of a novel habitat

DNA methylation is important to maintain genome stability, but alterations in genome-wide methylation patterns can produce widespread genomic effects, which have the potential to facilitate rapid adaptation. We investigate DNA methylation evolution in Arabidopsis thaliana during its colonization of the drought-prone Cape Verde Islands (CVI). We identified three high impact changes in genes linking histone modification to DNA methylation that underlie variation in DNA methylation within CVI. Gene body methylation is reduced in CVI relative to the Moroccan outgroup due to a 2.7-kb deletion between two VARIANT IN METHYLATION genes (VIM2 and VIM4) that causes aberrant expression of the VIM2/4 homologs. Disruptions of CHROMOMETHYLASE 2 (CMT2) and a newly identified DNA methylation modulator, F-BOX PROTEIN 5 (FBX5), which we validated using CRISPR mutant analysis, contribute to DNA methylation of transposable elements (TEs) within CVI. Overall, our results reveal rapid methylome evolution driven largely by high impact variants in three genes.

genetics↗

bioRxiv2025

Nanorate sequencing reveals the Arabidopsis somatic mutation landscape

The rate and spectrum of somatic mutations can diverge from that of germline mutations. This is because somatic tissues experience different mutagenic processes than germline tissues. Here, we use nanorate sequencing (NanoSeq) to identify somatic mutations in Arabidopsis shoots with high sensitivity. We report a somatic mutation rate of 3.6x10-8 mutations/bp, [~]4-5x the germline mutation rate. Somatic mutations displayed elevated signatures consistent with oxidative damage, UV damage, and transcription-coupled nucleotide excision repair. Both somatic and germline mutations were enriched in transposable elements and depleted in genes, but this depletion was greater in germline mutations. Somatic mutation rate correlated with proximity to the centromere, DNA methylation, chromatin accessibility, and gene/TE content, properties which were also largely true of germline mutations. We note DNA methylation and chromatin accessibility have different predicted effects on mutation rate for genic and non-genic regions; DNA methylation associates with a greater increase in mutation rate when in non-genic regions, and accessible chromatin associates with a lower mutation rate in non-genic regions but a higher mutation rate in genic regions. Together, these results characterize key differences and similarities in the genomic distribution of somatic and germline mutations.

genomics↗

bioRxiv2025

Using single-cell genomics to explore transcriptional divergence and cis-regulatory dynamics of duplicated genes

Gene duplication is a major source of evolutionary innovation, enabling the emergence of novel expression patterns and functions. Leveraging single-cell genomics, we investigated the transcriptional and cis-regulatory landscapes of duplicated genes in cultivated soybean (Glycine max), that has undergone two rounds of whole-genome duplication. Our analysis revealed extensive diversity of transcriptional profiles within and across tissues among duplicated gene pairs. Within-tissue divergence was largely attributable to genetic variation in their associated accessible chromatin regions (ACRs), where cis-regulatory elements reside, whereas cross-tissue divergence was more likely shaped by dynamics in ACR chromatin accessibility profiles across tissues. Distinct duplication mechanisms also likely give rise to different types of cis-regulatory variants, contributing variably to transcriptional divergence. By comparing ACRs associated with gene sets derived from the two rounds of whole-genome duplications and sharing a common ancestral gene, we found that most ACRs retained one or multiple corresponding duplicated sequences in which mutations gradually accumulated over time, while a subset likely arose de novo. Lastly, we traced the evolution of cell-type-specific expression and cell-type-specific ACRs within duplicated gene sets, illustrating a powerful framework for identifying candidate regulatory regions driving cell-type-specific expression. Collectively, our findings highlight the important role of cis- regulatory evolution in shaping transcriptional divergence in a spatiotemporal manner, uncovered with the resolution of single-cell genomics.

evolutionary biology↗

bioRxiv2025

Deciphering Transcription in Cryptosporidium parvum: Polycistronic Gene Expression and Chromatin Accessibility

Once considered rare in eukaryotes, polycistronic mRNA expression has been identified in kinetoplastids and, more recently, green algae, red algae, and certain fungi. This study provides comprehensive evidence supporting the existence of polycistronic mRNA expression in the apicomplexan parasite Cryptosporidium parvum. Leveraging long-read RNA-seq data from different parasite strains and using multiple long-read technologies, we demonstrate the existence of defined polycistronic transcripts containing 2-4 protein encoding genes, several validated with RT-PCR. Some polycistrons exhibit differential expression profiles, usually involving the generation of internal monocistronic transcripts at different times during development. ATAC-seq in sporozoites reveals that polycistronic transcripts usually have a single open chromatin peak at their 5-prime ends, which contains a single E2F binding site motif. Polycistronic genes do not appear enriched for either male or female exclusive genes. This study elucidates a potentially complex layer of gene regulation with distinct chromatin accessibility akin to monocistronic transcripts. This is the first report of polycistronic transcription in an apicomplexan and expands our understanding of gene expression strategies in this medically important organism. SignificanceCryptosporidium parvum is a parasite that causes human gastrointestinal disease, profoundly impacting infants and immunocompromised individuals worldwide. C. parvum isolation, culturing, cloning, and its compact 9.2 Mb genome pose challenges for research. We have discovered that, unlike most eukaryotes, which express one gene per mRNA, C. parvum exhibits widespread polycistronic transcription, whereby 10% of its protein encoding genes are expressed as multiple genes per single mRNA molecule. Mining the published C. parvum single-cell atlas with proxy sequences for polycistronic expression, we observed patterns of polycistron expression that vary with developmental stages, suggesting a role in the parasites lifecycle. By illuminating this unique aspect of C. parvum biology, our findings provide novel insights into Cryptosporidium gene expression.

genetics↗

bioRxiv2024

The genetic architecture of cell-type-specific cis-regulation

AbstractGene expression and complex phenotypes are determined by the activity of cis-regulatory elements. However, an understanding of how extant genetic variants affect cis regulation remains limited. Here, we investigated the consequences of cis-regulatory diversity using single-cell genomics of >0.7 million nuclei across 172 Zea mays (maize) inbreds. Our analyses pinpointed cis-regulatory elements distinct to domesticated maize and revealed how historical transposon activity has shaped the cis-regulatory landscape. Leveraging population genetics principles, we fine-mapped [~]22,000 chromatin accessibility-associated genetic variants with widespread cell-type-specific effects. Variants in TEOSINTE BRANCHED1/CYCLOIDEA/PROLIFERATING CELL FACTOR binding sites were the most prevalent determinants of chromatin accessibility. Finally, integrating chromatin accessibility-associated variants, organismal trait variation, and population differentiation revealed how local adaptation has rewired regulatory networks in unique cellular context to alter maize flowering.

genetics↗