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Abstract Detail


Thixton, Hana [1], Santee, Mathilda Viola [1], Freudenstein, John [2], Barrett, Craig [3].

A population perspective on plastome degradation in the mycoheterotrophic Corallorhiza maculata species complex.

Parasites typically display both morphological and genomic reduction however the full extent of genome degradation and morphological variation across populations is poorly understood. Mycoheterotrophic plants parasitize fungi for most or all their nutritional needs, providing a compelling model system to address questions of adaptive evolutionary consequences of genome reduction due to relaxation of purifying selection on photosynthetic function. While genome reduction has been well documented for many parasites, we lack a mechanistic understanding of how the process of rapid genome modification occurs in extant populations. We are using the widespread Corallorhiza maculata complex to address questions of plastome variation across the geographic range. This complex contains C. mertensiana, C. maculata var. maculata, C. maculata var. occidentalis, C. bulbosa, C. maculata var. mexicana, and C. macrantha. These species and intraspecific taxa vary in flowering time, floral morphology, geographic distribution, and fungal associations. Previous studies based on a limited sampling of complete plastid genome sequences provided robust branch support for relationships within the complex with a single, shared loss of photosynthesis in the fully mycoheterotrophic North American members (C. mertensiana, C. maculata vars. maculata and occidentalis), but the extent and degree of plastome modification have not been studied. Our goal is to quantify genomic and morphological variation in the C. maculata complex from populations across North America. We have prepared Illumina genomic libraries from 45 samples for the North American members, with deeper sampling from Oregon and California, USA. We will use floral morphometrics to test for associations between morphological distinctness and genomic relationships. We will assemble and annotate plastid genomes and compare these results to the partially mycoheterotrophic species from Mexico (C. bulbosa, C. maculata var. mexicana, and C. macrantha). From this comparative study, we will identify structural variation, pseudogenes, and genomic deletions within this complex. Additionally, we will utilize phylogenomic methods to characterize plastid genomic relationships among individuals. From preliminary results, we will design primers to test for a 16 kb inversion in the large single-copy region that putatively varies among populations in an expanded sampling of hundreds of individuals. The key findings from this study will allow for a population-based perspective on the process of rapid genome evolution below the species level, extending beyond what is known above the species level.

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1 - West Virginia University, Biology, 53 Campus Drive, Morgantown, WV, 26506, USA
2 - Ohio State University Herbarium, 1315 Kinnear Road, Columbus, OH, 43212, United States
3 - West Virginia University, 53 Campus Drive, Morgantown, West Virginia, 26506, United States

floral morphology

Presentation Type: Oral Paper
Session: PHYLOII, Phylogenomics II
Location: Virtual/Virtual
Date: Tuesday, July 20th, 2021
Time: 3:45 PM(EDT)
Number: PHYLOII004
Abstract ID:390
Candidate for Awards:None

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