Weak population spatial genetic structure and low infraspecific specificity for fungal partners in the rare mycoheterotrophic orchid Epipogium aphyllum

Abstract

Some plants abandoned photosynthesis and developed full dependency on fungi for nutrition. Most of the so-called mycoheterotrophic plants exhibit high specificity towards their fungal partners. We tested whether natural rarity of mycoheterotrophic plants and usual small and fluctuating population size make their populations more prone to genetic differentiation caused by restricted gene flow and/or genetic drift. We also tested whether these genetic characteristics might in turn shape divergent fungal preferences. We studied the mycoheterotrophic orchid Epipogium aphyllum, addressing the joint issues of genetic structure of its populations over Europe and possible consequences for mycorrhizal specificity within the associated fungal taxa. Out of 27 sampled E. aphyllum populations, nine were included for genetic diversity assessment using nine nuclear microsatellites and plastid DNA. Population genetic structure was inferred based on the total number of populations. Individuals from 17 locations were included into analysis of genetic identity of mycorrhizal fungi of E. aphyllum based on barcoding by nuclear ribosomal DNA. Epipogium aphyllum populations revealed high genetic diversity (uHe = 0.562) and low genetic differentiation over vast distances (FST = 0.106 for nuclear microsatellites and FST = 0.156 for plastid DNA). Bayesian clustering analyses identified only two genetic clusters, with a high degree of admixture. Epipogium aphyllum genets arise from panmixia and display locally variable, but relatively high production of ramets, as shown by a low value of rarefied genotypic richness (Rr = 0.265). Epipogium aphyllum genotype control over partner selection was negligible as (1) we found ramets from a single genetic individual associated with up to 68% of the known Inocybe spp. associating with the plant species, (2) and partner identity did not show any geographic structure. The absence of mosaicism in the mycorrhizal specificity over Europe may be linked to preferential allogamous habit of E. aphyllum and significant gene flow, which tend to promote host generalism.

In-depth analysis of genomes and functional genomics of orchid using cutting-edge high-throughput sequencing

“…The comparison of Platanthera zijinensis and Platanthera guangdongensis genomes indicated that mycoheterotrophy is linked to higher rates of gene loss and alternation, and that the deletion of most photoreceptor and auxin transporter genes might explain how fully mycoheterotrophic orchids look so different from other orchids. Some trehalase genes have grown, which makes sense since orchid non-endosperm seeds need carbohydrates from fungi to sprout when they are in the protocorm stage (Li M-H. et al, 2022;Minasiewicz et al, 2022).…”

New microsatellite loci to quantify genetic diversity of the photosymbiodeme-forming lichen Sticta canariensis

“…Due to their high polymorphism and Mendelian inheritance, microsatellites are a useful marker type for population genetic studies (Schlötterer 2000; Abdelkrim et al 2009) and are an inexpensive alternative to whole genome sequencing. Microsatellite markers are also a widely used tool for fungal genetic studies, specifically for plant pathogens, mycorrhizal fungi and lichens (Tenzer et al 1999; Werth 2010; Minasiewicz et al 2022; Velasco-Anacona et al 2022). In lichens they are highly species-specific and have proved useful for assessing genetic variation within species at different spatial scales (Walser et al 2003; Werth 2010).…”