Biology subjects

Niederhuth, C. E.

Publications and source records attributed to Niederhuth, C. E..

4 recordsLinked to original sources

bioRxiv2023

The role of breakpoint mutations, supergene effects, and ancient nested rearrangements in the evolution of adaptive chromosome inversions in the yellow monkey flower, Mimulus guttatus

Chromosomal inversion polymorphisms are ubiquitous across the diversity of diploid organisms and play a significant role in the evolution of adaptations in those species. Inversions are thought to operate as supergenes by trapping adaptive alleles at multiple linked loci through the suppression of recombination. While there is now considerable support for the supergene mechanism of inversion evolution, the extent to which inversions trap pre-existing adaptive genetic variation versus accumulate new adaptive variants over time remains unclear. In this study, we report new insights into the evolutionary dynamics of a locally adaptive chromosomal inversion polymorphism (inv_chr8A), which contributes to the evolutionary divergence between coastal perennial and inland annual ecotypes of the yellow monkeyflower, Mimulus guttatus. This research was enabled by the sequencing, assembly, and annotation of new annual and perennial genomes of M. guttatus using Oxford Nanopore long-read sequencing technology. In addition to the adaptive inv_chr8A inversion, we identified three other large inversion polymorphisms, including a previously unknown large inversion (inv_chr8B) nested within the inv_chr8A. Through population genomic analyses and comparative genomics, we determined that the nested inv_chr8B inversion is significantly older than the larger chromosomal inversion in which it resides. We also evaluated key candidate genes involved in gibberellin biosynthesis and anthocyanin regulation, which we hypothesize to underlie the adaptive phenotypic effects of the inv_chr8A inversion. Although little evidence was found to suggest that inversion breakpoint mutations drive adaptive phenotypic effects, our findings support the supergene mechanism of adaptive evolution as a dynamic and continuous process.

genomics↗

bioRxiv2022

Single-cell transcriptomics of the Arabidopsis floral abscission zone

Abscission is the programmed separation of plant organs. It is widespread in the plant kingdom with important functions in development and environmental response. In Arabidopsis, abscission of floral organs (sepals, petals, and stamens) is controlled by two receptor-like protein kinases HAESA (HAE) and HAESA LIKE-2 (HSL2), which orchestrate the programmed dissolution of the abscission zone connecting floral organs to the developing fruit. In this work, we use single-cell RNA-Sequencing to characterize the core HAE/HSL2 abscission gene expression program. We identify the MAP KINASE PHOSPHATASE-1/MKP1 gene as a negative regulator of this pathway. MKP1 acts prior to activation of HAE/HSL2 signaling to establish a signaling threshold required for the initiation of abscission. By analogy to electrical circuit control, we liken MKP1 to a molecular grounding mechanism that dissipates errant pathway activation absent HAE/HSL2 signaling. Furthermore, we use single-cell data to identify genes expressed in two sub-populations of abscission zone cells: those proximal and those distal to the plane of separation. We identify INFLORESCENCE DEFICIENT IN ABSCISSION/IDA, encoding the activating ligand of HAE/HSL2, as one of the mRNAs most highly enriched in distal abscission zone cells at the base of the abscising organs. We show how this expression pattern forms a biophysical circuit breaker whereby, when the organ is shed, the source of the IDA peptide is removed, leading to cessation of HAE/HSL2 signaling. Overall, this work provides insight into the multiple control mechanisms acting on the abscission-signaling pathway.

plant biology↗

bioRxiv2022

Regulatory dynamics distinguishing desiccation tolerance strategies within resurrection grasses

Desiccation tolerance has evolved recurrently in grasses using two unique strategies to mitigate photooxidative damage under anhydrobiosis. The grass Oropetium thomaeum protects and retains chlorophyll, thylakoids, and the photosynthetic apparatus during desiccation (Homoiochlorophyly), while Eragrostis nindensis degrades and resynthesizes these components under desiccation and rehydration (Poikilochlorophyly). Here, we surveyed chromatin architecture and gene expression during desiccation in these two closely related species to identify regulatory dynamics underlying the distinct desiccation tolerance strategies in grasses. In both grasses, we observed a strong association between nearby chromatin accessibility and gene expression in desiccated tissues compared to well-watered, reflecting an unusual chromatin stability under anhydrobiosis. Integration of chromatin accessibility (ATACseq) and expression data (RNAseq) revealed a core desiccation response across these two grasses including many genes with binding sites for the core seed development transcription factor ABI5. O. thomaeum had a unique set of desiccation induced genes and regulatory elements associated with photoprotection, pigment biosynthesis, and response to high light, reflecting its adaptation of homoiochlorophyly. A tandem array of early light induced proteins (ELIPs) had massive shifts in gene expression and chromatin openness under desiccation in only O. thomaeum, and ELIPs acquired a novel desiccation related cis-regulatory motif, reflecting regulatory neofunctionalization during the evolution of desiccation tolerance. Together, our results highlight the complex regulatory and expression dynamics underlying desiccation tolerance in grasses.

plant biology↗

bioRxiv2020

DNA methylation signatures of duplicate gene evolution in angiosperms

Gene duplication is a source of evolutionary novelty. DNA methylation may play a role in the evolution of duplicate genes through its association with gene expression. While this relationship is examined to varying extent in a few individual species, the generalizability of these results at either a broad phylogenetic scale with species of differing duplication histories or across a population, remains unknown. We apply a comparative epigenomics approach to 43 angiosperm species across the phylogeny and a population of 928 Arabidopsis thaliana accessions, examining the association of DNA methylation with paralog evolution. Genic DNA methylation is differentially associated with duplication type, the age of duplication, sequence evolution, and gene expression. Whole genome duplicates are typically enriched for CG-only gene-body methylated or unmethylated genes, while single-gene duplications are typically enriched for non-CG methylated or unmethylated genes. Non-CG methylation, in particular, was characteristic of more recent single-gene duplicates. Core angiosperm gene families are differentiated into those which preferentially retain paralogs and duplication-resistant families, which convergently revert to singletons following duplication. Duplication-resistant families which still have paralogous copies are, uncharacteristically for core angiosperm genes, enriched for non-CG methylation. Non-CG methylated paralogs have higher rates of sequence evolution, higher frequency of presence-absence variation, and more limited expression. This suggests that silencing by non-CG methylation may be important to maintaining dosage following duplication and be a precursor to fractionation. Our results indicate that genic methylation marks differing evolutionary trajectories and fates between paralogous genes and have a role in maintaining dosage following duplication.

plant biology↗