Biology subjects

Khost, D. E.

Publications and source records attributed to Khost, D. E..

3 recordsLinked to original sources

bioRxiv2026

Independent evolution of harmala alkaloids in medicinal Syrian rue and ayahuasca plants

Plants from distantly related lineages can produce identical neuroactive molecules, many of which have been independently adopted across human societies for their medicinal and cognition-altering effects. This phenomenon is exemplified by the traditional use of Syrian rue (Peganum harmala) and the ayahuasca vine (Banisteriopsis caapi) for medicine and ritual. Despite diverging over 100 million years ago and inhabiting different continents and climates, both plants synthesize harmala alkaloids (HAs), which inhibit human monoamine oxidase and exhibit diverse neuroactive effects. Here, we combine gene expression analyses, genomics, and enzyme characterization to elucidate HA biosynthesis for both Syrian rue and ayahuasca vine. We reveal multiple layers of biochemical and genetic convergence in these pathways, including independent duplication and neofunctionalization of an ancestral enzyme from serotonin biosynthesis, and lineage-specific repurposing of primary metabolic genes to generate a reactive precursor for alkaloid scaffold formation. Our study resolves biosynthetic routes to HAs in two medicinal plants and demonstrates convergent evolution of specialized metabolism at the levels of enzymes, pathways, and genomes.

biochemistry↗

bioRxiv2026

Unmasking the large and highly repetitive genome of Phlox reveals a complex evolutionary history of speciation with gene flow

The large size and high repetitive content of many plant genomes have hindered elucidation of how the fundamental processes of evolution give rise to speciation. Here we present chromosome-level assemblies of 6 gigabase genomes for four closely related Phlox wildflower species. We generate extensive population genetic data for the three well-studied annual species P. drummondii, P. cuspidata, and P. roemeriana, including structural variation from whole-genome long-read resequencing data. The whole-genome assemblies reveal extensive differences in amount and distribution of genetic variation within and between species, reflective of differences in life-history strategies, mating systems, and edaphic specialization. The population genetic data exposes a history of widespread and consistent gene flow between all three annual Phlox species throughout their divergence and speciation. Our unmasking of structural variants and repetitive elements exposes rich and dynamic forms of genetic variation that show strong phylogenetic signal and pervasive patterns of gene flow. Our results lay a foundation for untangling the highly complex genomes of plants to make advancements in our understanding of the processes of speciation and divergence.

evolutionary biology↗

bioRxiv2019

Dynamic evolution of euchromatic satellites on the X chromosome in Drosophila melanogaster and the simulans clade

Satellite DNAs (satDNAs) are among the most dynamically evolving components of eukaryotic genomes and play important roles in genome regulation, genome evolution, and speciation. Despite their abundance and functional impact, we know little about the evolutionary dynamics and molecular mechanisms that shape satDNA distributions in genomes. Here we use high-quality genome assemblies to study evolutionary dynamics of two complex satDNAs, Rsp-like and 1.688 gm/cm3, in Drosophila melanogaster and its three nearest relatives in the simulans clade. We show that large blocks of these repeats are highly dynamic in the heterochromatin, where their genomic location varies across species. We discovered that small blocks of satDNA that are abundant in X chromosome euchromatin are similarly dynamic, with repeats changing in abundance, location, and composition among species. We detail the proliferation of a rare satellite (Rsp-like) across the X chromosome in D. simulans and D. mauritiana. Rsp-like spreads by inserting into existing clusters of the older, more abundant 1.688 satellite, in events that were likely facilitated by microhomology-mediated repair pathways. We show that Rsp-like is abundant on extrachromosomal circular DNA in D. simulans, which may have contributed to its dynamic evolution. Intralocus satDNA expansions via unequal exchange and the movement of higher-order repeats also contribute to the fluidity of the repeat landscape. We find evidence that euchromatic satDNA repeats experience cycles of proliferation and diversification somewhat analogous to bursts of transposable element proliferation. Our study lays a foundation for mechanistic studies of satDNA proliferation and the functional and evolutionary consequences of satDNA movement.

genomics↗