Biology subjects

Petrus, S.

Publications and source records attributed to Petrus, S..

6 recordsLinked to original sources

bioRxiv2025

Triploidy is prominent in the duckweed Lemna minor complex

Duckweeds (Lemnaceae Martinov) are aquatic monocotyledonous flowering plants comprising five genera and 35 recognized species, known for being the smallest and fastest-growing flowering plants on Earth. Many species are morphologically indistinguishable due to their highly reduced structures, yet molecular evidence suggests that visually similar clones may represent distinct species or hybrids. For example, clonal accessions of the globally distributed Lemna minor in the Landolt Duckweed Collection exhibit genome size variations of several hundred megabases (Mb), raising questions about their taxonomic classification and evolutionary origins. We analyzed 58 presumed L. minor clones to resolve these relationships using a comprehensive suite of methods, including whole-genome sequencing (WGS), flow-cytometric genome size measurements, molecular markers, chromosome counting, and genomic in situ hybridization (GISH). Our findings reveal extensive genome plasticity within the "Lemna minor complex," identifying diploid and triploid L. minor clones, as well as di-haploid and triploid interspecific hybrids called L. x japonica (L. minor x L. turionifera), L. x mediterranea (L. minor x L. gibba), and a novel African-clade distinct from known L. minor lineages. Triploidy was prevalent, occurring in 29% of the clones, and was associated with enhanced growth under optimal conditions but reduced performance under high light and temperature. These findings highlight the widespread role of triploidy, cryptic species, and hybridization in the L. minor complex, emphasizing the importance of multiple approaches for accurately classifying duckweed species and understanding their evolutionary trajectories.

plant biology↗

bioRxiv2024

Chromosome-level baobab (Adansonia digitata) genome illuminates its evolutionary insights

AbstractBaobab, Adansonia digitata, is a long-lived tree endemic to Africa that holds great economic, ecological, and cultural value. However, our knowledge of its genomic features, evolutionary history, and diversity is limited, rendering it orphaned scientifically. We generated a haploid chromosome-level reference genome anchored into 42 chromosomes for A. digitata, as well as draft assemblies for a sibling tree, two trees from distinct locations in Africa, and a related species, A. za from Madagascar. Unlike any other plant to date, DNA transposable elements (TEs) make up 33% of the A. digitata genome compared to only 10% long terminal repeat retrotransposons (LTR-RTs), which are usually predominant in plant genomes. Baobab has undergone a whole genome duplication (WGD) shared with the Malvoideae [~]30 million years ago (MYA), as well as a confirmed autotetraplody event 3-4 million MYA that coincides with the most recent burst of TE insertions. Resequencing 25 A. digitata trees from Africa revealed three subpopulations that suggest gene flow through most of West Africa but separated from East Africa. Gene enrichment analysis for baobab-specific and high fixation index (Fst) suggested baobab may have retained multiple copies of circadian, light and growth genes to coordinate genome protection for longevity through the UV RESISTANCE LOCUS 8 (UVR8) and synchronizing flower development with pollinators. This study lays the groundwork for the creation of breeding resources and the conservation of baobab biodiversity.

genomics↗

bioRxiv2024

Telomere Length in Plants Estimated with Long Read Sequencing

Telomeres play an important role in chromosome stability and their length is thought to be related to an organisms lifestyle and lifespan. Telomere length is variable across plant species and between cultivars of the same species, possibly conferring adaptive advantage. However, it is not known whether telomere length is related to lifestyle or life span across a diverse array of plant species due to the lack of information on telomere length in plants. Here we leverage genomes assembled with long read sequencing data to estimate telomere length by chromosome. We find that long read assemblies based on Oxford Nanopore Technologies (ONT) accurately predict telomere length in the two model plant species Arabidopsis thaliana and Oryza sativa matching lab-based length estimates. We then estimate telomere length across an array of plant species with different lifestyles and lifespans and find that in general gymnosperms have shorter telomeres compared to eudicots and monocots. Crop species frequently have longer telomeres than their wild relatives, and species that have been maintained clonally such as hemp have long telomeres possibly reflecting that this lifestyle requires long term chromosomal stability.

plant biology↗

bioRxiv2023

PanKmer: k-mer based and reference-free pangenome analysis

SummaryPangenomes are replacing single reference genomes as the definitive representation of DNA sequence within a species or clade. Pangenome analysis predominantly leverages graph-based methods that require computationally intensive multiple genome alignments, do not scale to highly complex eukaryotic genomes, limit their scope to identifying structural variants (SVs), or incur bias by relying on a reference genome. Here, we present PanKmer, a toolkit designed for reference-free analysis of pangenome datasets consisting of dozens to thou-sands of individual genomes. PanKmer decomposes a set of input genomes into a table of observed k-mers and their presence-absence values in each genome. These are stored in an efficient k-mer index data format that encodes SNPs, INDELs, and SVs. It also includes functions for downstream analysis of the k-mer index, such as calculating sequence similarity statistics between individuals at whole-genome or local scales. For example, k-mers can be "anchored" in any individual genome to quantify sequence variability or conservation at a specific locus. This facilitates workflows with various biological applications, e.g. identifying cases of hybridization between plant species. PanKmer provides researchers with a valuable and convenient means to explore the full scope of genetic variation in a population, without reference bias. Availability and implementationPanKmer is implemented as a Python package with components written in Rust, released under a BSD license. The source code is available from the Python Package Index (PyPI) at https://pypi.org/project/pankmer/ as well as Gitlab at https://gitlab.com/salk-tm/pankmer. Full documentation is available at https://salk-tm.gitlab.io/pankmer/. Supplementary informationSupplementary data are available online

bioinformatics↗

bioRxiv2021

Chromosome-level genome assembly of a human fungal pathogen reveals synteny among geographically distinct species

Histoplasma capsulatum, a dimorphic fungal pathogen, is the most common cause of fungal respiratory infections in immunocompetent hosts. Histoplasma is endemic in the Ohio and Mississippi River Valleys in the United States and also distributed worldwide. Previous studies revealed at least eight clades, each specific to a geographic location: North American classes 1 and 2 (NAm 1 and NAm 2), Latin American groups A and B (LAm A and LAm B), Eurasian, Netherlands, Australian and African, and an additional distinct lineage (H81) comprised of Panamanian isolates. Previously assembled Histoplasma genomes are highly fragmented, with the highly repetitive G217B (NAm 2) strain, which has been used for most whole genome-scale transcriptome studies, assembled into over 250 contigs. In this study, we set out to fully assemble the repeat regions and characterize the large-scale genome architecture of Histoplasma species. We re-sequenced five Histoplasma strains (WU24 (NAm 1), G217B (NAm 2), H88 (African), G186AR (Panama), and G184AR (Panama)) using Oxford Nanopore Technologies long-read sequencing technology. Here we report chromosomal-level assemblies for all five strains, which exhibit extensive synteny among the geographically distant Histoplasma isolates. The new assemblies revealed that RYP2, a major regulator of morphology and virulence, is duplicated in G186AR. In addition, we mapped previously generated transcriptome datasets onto the newly assembled chromosomes. Our analyses revealed that the expression of transposons and transposon-embedded genes are upregulated in yeast phase compared to mycelial phase in G217B and H88 strains. This study provides an important resource for fungal researchers and further highlights the importance of chromosomal-level assemblies in analyzing high-throughput datasets. ImportanceHistoplasma species are dimorphic fungi causing significant morbidity and mortality worldwide. These fungi grow as mold in the soil and as budding yeast within the human host. Histoplasma can be isolated from soil in diverse regions, including North America, South America, Africa and Europe. Phylogenetically distinct species of Histoplasma have been isolated and sequenced. However, for the commonly used strains, genome assemblies have been fragmented, leading to underutilization of genome-scale data. This study provides chromosome-level assemblies of the commonly used Histoplasma strains using long-read sequencing technology. Comparative analysis of these genomes shows largely conserved gene order within the chromosomes. Mapping existing transcriptome data on these new assemblies reveals clustering of transcriptionally co-regulated genes. Results of this study highlight the importance of obtaining chromosome-level assemblies in understanding the biology of human fungal pathogens.

microbiology↗

bioRxiv2019

Temporal, environmental, and biological drivers of the mucosal microbiome in a wild marine fish, Scomber japonicus

Changing ocean conditions driven by anthropogenic activity may have a negative impact on fisheries by increasing stress and disease with the mucosal microbiome as a potentially important intermediate role. To understand how environment and host biology drives mucosal microbiomes in a marine fish, we surveyed five body sites (gill, skin, digesta, GI, and pyloric caeca) from 229 Pacific chub mackerel, Scomber japonicus, collected across 38 time points spanning one year from the Scripps Institution of Oceanography Pier, making this the largest and longest wild marine fish microbiome survey. Mucosal sites had unique communities significantly different from the surrounding sea water and sediment communities with over 10 times more diversity than sea water alone. Although, external surfaces such as skin and gill were more similar to sea water, digesta was similar to sediment. Both alpha and beta diversity of the skin and gill was explained by environmental and biological factors, especially sea surface temperature, chlorophyll a, and fish age, consistent with an exposure gradient relationship. We verified that seasonal microbial changes were not confounded by migrations of chub mackerel sub-populations by nanopore sequencing a 14 769 bp region of the 16 568 bp mitochondria. A cosmopolitan pathogen, Photobacterium damselae, was prevalent across multiple body sites all year, but highest in the skin, GI, and digesta between June and September. Our study evaluates the extent which the environment and host biology drives mucosal microbial ecology, establishing a baseline for long term monitoring surveys for linking environment stressors to mucosal health of wild marine fish.

ecology↗