Biology subjects

Olsen, K. M.

Publications and source records attributed to Olsen, K. M..

5 recordsLinked to original sources

bioRxiv2026

Cyanogenic clovers invest more in rhizobia but do not affect rhizobium evolution

Nitrogen governs the interactions between leguminous plants and their nitrogen-fixing resource mutualists, rhizobia. While most work has focused on how soil nitrogen availability shapes the ecology and evolution of the legume-rhizobium mutualism, the nitrogen demands of plants may also influence the mutualism. Plants differ in nitrogen demand, in part because of variation in specialized metabolite production, particularly in species that produce nitrogen-based defense compounds such as cyanogenic glycosides. Plants with high nitrogen demand might be expected to be more reliant on rhizobia, potentially investing more in rhizobia and exerting stronger preferences for high-quality mutualists. Here, we use white clover (Trifolium repens), which is polymorphic for cyanogenesis, from two biparental F3 mapping populations to examine whether nitrogen-based chemical defenses affect plant investment in the mutualism or rhizobium evolution. By inoculating cyanogenic and acyanogenic clover lines with a single strain of Rhizobium leguminosarum, we found that cyanogenic clovers produced larger root nodules than acyanogenic clover, suggesting that cyanogensis is associated with increased investment in rhizobia. Greater investment in rhizobia could select for more cooperative mutualists if accompanied by partner choice or sanctions allowing plants to preferentially reward more cooperative rhizobia. We conditioned soils with cyanogenic and acyanogenic clover lines for five plant growth cycles and compared the partner quality of rhizobia isolated from these soils. Rhizobia evolved in association with cyanogenic versus acyanogenic clover did not differ in quality. Overall, our results show that N-based anti-herbivore defense traits can influence plant investment in resource mutualists but suggest that differences in investment do not necessarily translate into long-term evolutionary changes in mutualist quality.

ecology↗

bioRxiv2025

Digging into the general dynamic model: Island ontogeny predicts shifting micro-evolutionary processes in a Mascarene flowering plant radiation

AO_SCPLOWBSTRACTC_SCPLOWIsland studies have been integral in the development of process-oriented biodiversity models such as the general dynamic model (GDM) of oceanic island biogeography. While empirical tests of the GDM primarily come from phylogeographic studies, tests incorporating comprehensive population-level sampling of island radiations are rare. In this study, we elucidate the evolutionary processes driving the diversification of Hibiscus section Lilibiscus in the Mascarene archipelago using population-level sampling and 2bRAD sequencing. Our goals were to: 1) assess species relationships and resolve taxonomic issues; 2) test patterns of intra- and interspecific genetic differentiation under a model of shifting speciation processes as islands age; and 3) utilize demographic modeling to infer the relative divergence times of populations in the archipelago. We found the Mascarene radiation of sect. Lilibiscus to be monophyletic and confirmed the presence of six morphologically distinct species. Species richness and phylogenetic relationships supported the expectations of the GDM. Namely, we found that morphologically similar populations of the same species on the intermediate-aged island, Mauritius, diverged earlier and showed greater divergence than morphologically disparate species on the youngest Mascarene island, Reunion. These patterns are consistent with the hypothesis that ecological selection may be affecting speciation on the youngest island, drift may be the most important force on the middle-aged island. Although not tested here, given that the oldest island is in a late stage of subsidence, extinction may be the most important evolution force occurring on the oldest island, consistent with the expectation that evolutionary processes occurring across each of these islands may be influenced by ontogenetic stage. We also found evidence that some species in the group may be naturally rare, suggesting that the rarity of species may not only be from recent habitat loss. Our study is the first to use population-level data to test complex predictions of the GDM and demonstrate that the most important evolutionary processes shift depending on island ontogeny.

evolutionary biology↗

bioRxiv2024

Receptor-ligand interactions in plant inmate immunity revealed by AlphaFold protein structure prediction

One of the common mechanisms to trigger plant innate immunity is recognition of pathogen avirulence gene products directly by products of major resistance (R) genes in a gene for gene manner. In the USA, the R genes, Pik-s, PiKh/m, and Pi-ta, Pi-39(t), and Ptr genes have been effectively deployed to prevent the infections of M. oryzae races, IB49, and IC17 for some time. Pi-9 is only recently being deployed to provide overlapped and complimentary resistance to Magnaporthe oryzae races IB49, IC17 and IE1k in the USA. Pi-ta, Pi-39(t), Pi9 are major nuclear binding site-leucine rich (NLR) proteins, and Ptr is an atypical R protein with 4 armadillo repeats. AlphaFold is an artificial intelligence system that predicts a protein 3D structure from its amino acid sequence. Here we report genome sequence analyses of the effectors and avirulence (AVR) genes, AVR-Pita and AVR-Pik, and AVR-Pi9, in 3 differential M. oryzae races. Using AlphaFold 2 and 3 we find strong evidence of direct interactions of products of resistance genes Pi-ta and Pik with M. oryzae avirulence (AVR) genes, AVR-Pita and AVR-Pik respectively. We also found that AVR-Pita interacts with Pi-39(t) and Ptr, and Pi9 interacts with both AVR-Pi9 and AVR-Pik. Validation of direct interactions of two pairs of R and AVR proteins supported a direct interaction mechanism of plant innate immunity. Detecting interaction of both Ptr and Pi39(t) with AVR-Pita, and Pi-9 with both AVR-Pi9 and AVR-Pik, revealed a new insight into recognition of pathogen signaling molecules by these host R genes in triggering plant innate immunity.

molecular biology↗

bioRxiv2023

Haplotype-resolved, chromosome-level assembly of white clover (Trifolium repens L., Fabaceae)

BackgroundWhite clover (Trifolium repens L.; Fabaceae) is an important forage and cover crop in agricultural pastures around the world, and is increasingly used in evolutionary ecology and genetics to understand the genetic basis of adaptation. Historically, improvements in white clover breeding practices and assessments of genetic variation in nature have been hampered by a lack of high-quality genomic resources for this species, owing in part to its high heterozygosity and allotetraploid hybrid origin. FindingsHere, we use PacBio HiFi and chromosome conformation capture (Omni-C) technologies to generate a chromosome-level, haplotype-resolved genome assembly for white clover totaling 998 Mbp (scaffold N50 = 59.3 Mbp) and 1 Gbp (scaffold N50 = 58.6 Mbp) for haplotypes 1 and 2, respectively, with each haplotype arranged into 16 chromosomes (8 per subgenome). We additionally provide a functionally annotated haploid mapping assembly (968 Mbp, scaffold N50 = 59.9 Mbp), which drastically improves on the existing reference assembly in both contiguity and assembly accuracy. We annotated 78,174 protein-coding genes, resulting in protein BUSCO completeness scores of 99.6% and 99.3% against the embryophyta_odb10 and fabales_odb10 lineage datasets, respectively. ConclusionsWe provide two white clover genome assemblies as part of this project: (1) a haplotype-resolved, chromosome-level assembly, and (2) a functionally annotated haploid mapping assembly. These assemblies place white clover among the best sequenced legumes to date, and one of the best assemblies for a plant of recent polyploid origins. This work promises to facilitate ongoing and future work in agricultural and evolutionary genetics in this agronomically and ecologically important species.

genomics↗

bioRxiv2021

Intraspecific variation in elemental accumulation and its association with salt tolerance in Paspalum vaginatum

Most plant species, including most crops, perform poorly in salt-affected soils because high sodium levels are cytotoxic and can disrupt uptake of water and important nutrients. Halophytes are species that have evolved adaptations to overcome these challenges and may be a useful source of knowledge for salt tolerance mechanisms and genes that may be transferable to crop species. The salt content of saline habitats can vary dramatically by location, providing ample opportunity for different populations of halophytic species to adapt to their local salt concentrations; however, the extent of this variation, and the physiology and polymorphisms that drive it, remain poorly understood. Differential accumulation of inorganic elements between genotypes or populations may play an important role in local salinity adaptation. To test this, we investigated the relationships between population structure, tissue ion concentrations (i.e., ionomic profiles) and salt tolerance in 17 "fine-textured" genotypes of the halophytic turfgrass seashore paspalum (Paspalum vaginatum Swartz). A high-throughput ionomics pipeline was used to quantify the shoot concentration of 18 inorganic elements across three salinity treatments. We found a significant relationship between population structure and ion accumulation, with strong correlations between principal components derived from genetic and ionomic data. Additionally, genotypes with higher salt tolerance accumulated more K and Fe and less Ca than less tolerant genotypes. Together these results indicate that differences in ion accumulation between P. vaginatum populations may reflect locally adapted salt stress responses.

plant biology↗