Evolution and Networks in Ancient and Widespread Symbioses Between Mucoromycotina and Liverworts
Total Page：16
File Type：pdf, Size：1020Kb
Mycorrhiza (2019) 29:551–565 https://doi.org/10.1007/s00572-019-00918-x ORIGINAL ARTICLE Evolution and networks in ancient and widespread symbioses between Mucoromycotina and liverworts William R. Rimington1,2,3 & Silvia Pressel2 & Jeffrey G. Duckett2 & Katie J. Field4 & Martin I. Bidartondo1,3 Received: 29 May 2019 /Accepted: 13 September 2019 /Published online: 13 November 2019 # The Author(s) 2019 Abstract Like the majority of land plants, liverworts regularly form intimate symbioses with arbuscular mycorrhizal fungi (Glomeromycotina). Recent phylogenetic and physiological studies report that they also form intimate symbioses with Mucoromycotina fungi and that some of these, like those involving Glomeromycotina, represent nutritional mutualisms. To compare these symbioses, we carried out a global analysis of Mucoromycotina fungi in liverworts and other plants using species delimitation, ancestral reconstruction, and network analyses. We found that Mucoromycotina are more common and diverse symbionts of liverworts than previously thought, globally distributed, ancestral, and often co-occur with Glomeromycotina within plants. However, our results also suggest that the associations formed by Mucoromycotina fungi are fundamentally different because, unlike Glomeromycotina, they may have evolved multiple times and their symbiotic networks are un-nested (i.e., not forming nested subsets of species). We infer that the global Mucoromycotina symbiosis is evolutionarily and ecolog- ically distinctive. Keywords Fine root endophytes . Glomeromycotina . Liverworts . Mucoromycotina . Networks . Terrestrialization Introduction (Pirozynski and Malloch 1975). This hypothesis posits that Precambrian green algae, the ancestors of land plants, were To what extent did fungi influence the conquest of land and able to colonize land successfully by entering into partner- greening of the planet by plants some 500 million years ago? ships with fungi. The fungi provided early rootless plants with This remains one of the most critical questions in land plant nutrients and water in exchange for photosynthesis-derived evolution ever since the idea of fungal-assisted plant carbohydrates. Following terrestrialization, this relationship terrestrialization was first proposed over 40 years ago evolved into mycorrhizal symbioses, now present in more than 85% of plants (Brundrett and Tedersoo 2018). Of these, Electronic supplementary material The online version of this article arbuscular mycorrhizas (AM) formed by Glomeromycotina (https://doi.org/10.1007/s00572-019-00918-x) contains supplementary fungi are by far the most widespread, occurring in at least material, which is available to authorized users. 72% of vascular plants (Brundrett and Tedersoo 2018). Liverworts are one of the three groups of bryophytes, or * William R. Rimington non-vascular plants, alongside mosses and hornworts. Though [email protected] the order of divergence of these groups remains under active * Martin I. Bidartondo debate (Puttick et al. 2018; Rensing 2018; de Sousa et al. [email protected] 2019), bryophytes are generally regarded as some of the ear- 1 Department of Life Sciences, Imperial College London, liest terrestrial plants (Renzaglia et al. 2018) and have provid- London SW7 2AZ, UK ed invaluable insights into the origin and evolution of key land 2 Department of Life Sciences, Algae, Fungi and Plants Division, plant innovations including mycorrhizas (e.g., Wang et al. Natural History Museum, London, London SW7 5BD, UK 2010; Field et al. 2015a, b, 2016, 2019). Indeed, 3 Comparative Plant and Fungal Biology, Royal Botanic Gardens, Glomeromycotina colonization in liverworts (Ligrone et al. Kew, Richmond TW9 3DS, UK 2007), together with the dominance of AM in extant land plant 4 Centre for Plant Sciences, Faculty of Biological Sciences, University lineages, and their putative occurrence in fossils (Taylor et al. of Leeds, Leeds LS2 9JT, UK 1995) have long supported the paradigm that 552 Mycorrhiza (2019) 29:551–565 Glomeromycotina formed the ancestral plant-fungus symbio- rDNA, species delimitation, and ancestral reconstruction, we sis (Smith and Read 2008). However, this consensus, dating aimed to shed light on this symbiosis by revealing its diversity over 20 years, was challenged in 2011 by a proposal, using and global distribution and comparing it to the symbiosis liverworts as a proxy for the first land plants, that formed by Glomeromycotina (Rimington et al. 2018). We also Glomeromycotina-plant mutualism was predated by symbio- present a first network analysis of fungal interactions with ses involving Endogonales belonging to Mucoromycotina non-vascular plants. Network analysis allows visualization (Bidartondo et al. 2011). Supporting physiological and phylo- and quantification of how members of a network interact genetic evidence has since accumulated rapidly (Field et al. and it has become popular across biotic interactions, including 2015a; Feijen et al. 2018; Hoysted et al. 2018). mycorrhizas, to show which plants interact with which fungi, Mucoromycotina fungi have been shown to colonize the and vice versa, and to infer symbiotic ecology and evolution earliest-diverging liverwort clade, the Haplomitriopsida (Southworth et al. 2005; Bascompte and Jordano 2014;van (Bidartondo et al. 2011), Koch’s postulates have been ful- der Heijden et al. 2015). Plant and fungal taxa represent nodes, filled, and isotope tracer experiments have demonstrated bidi- and patterns of fungal occurrences are links connecting the rectional nutritional exchange between some two sets (fungi vs. plants or vice versa) of nodes. Once nodes Haplomitriopsida and Mucoromycotina (Field et al. 2015b). and links are established, mycorrhizal network architecture Mucoromycotina fungi also colonize hornworts (Desirò et al. can be quantified and compared. 2013) and the earliest-diverging vascular plants, lycophytes, and ferns (Rimington et al. 2015), indicating that these fungi are widespread symbionts of ancient plant lineages. Methods Hornworts, lycophytes, and some non-Haplomitriopsida liv- erworts (Marchantiopsida and Pelliidae) are simultaneously Plant material and symbiotic fungi colonized by both Mucoromycotina and Glomeromycotina; in liverworts, these “dual” colonizations have been shown to We focused on liverwort clades (Haplomitriopsida, be more nutritionally beneficial than those involving only one Marchantiopsida (complex thalloids), and Pelliidae (simple fungal lineage (Field et al. 2016, 2019). thalloids, within Jungermanniopsida)) with Mucoromycotina While the Glomeromycotina have been studied intensively associations. The largest group of liverworts, the leafy for decades, the Mucoromycotina remain relatively poorly Jungermanniidae, forms associations only with ascomycetes understood. Mucoromycotina and Glomeromycotina have re- or basidiomycetes or lack fungi (Pressel et al. 2010). cently been placed in the phylum Mucoromycota (Spatafora Liverwort collection sites were in 24 countries and all conti- et al. 2016, but see Tedersoo et al. 2018), having been previ- nents except Antarctica (Table S1). In total, 674 mature liver- ously either an unplaced subphylum (Mucoromycotina) or a wort gametophytes were newly collected from the classes monophyletic phylum (Glomeromycota) (Schüßler et al. Haplomitriopsida (72 samples), Marchantiopsida (411), and 2001; Hibbett et al. 2007). Of the three Mucoromycotina or- Pelliidae (191). Specimen vouchers have been deposited at ders (Endogonales, Mucorales, and Umbelopsidales), only the Natural History Museum, London. Using the latest no- members of Endogonales (Endogonaceae and menclatures, samples were assigned to 85 species Densosporaceae) are known to enter into symbioses with (Soderstrom et al. 2016; Stotler and Crandall-Stotler 2017). plants (Desirò et al. 2017), being common endosymbionts of Only genus-level identification was possible for 49 samples, early-diverging lineages (liverworts, hornworts, lycophytes, so the total number of species is likely higher than 85. Within and ferns) (Bidartondo et al. 2011;Desiròetal.2013; 3 days of collection liverwort samples were cleaned of soil and Rimington et al. 2015) with some members ectomycorrhizal debris using water and forceps. Then, the thallus midrib was with trees (Walker 1985; Desirò et al. 2017; Yamamoto et al. dissected as this is where fungal colonization is highest 2017). Recent reports indicate that fine root endophytes, (Pressel et al. 2010). Dissection was performed by removing arbuscule-forming fungi found throughout vascular plants the wings and rhizoids and cutting thallus sections ca. 3 mm2 (Orchard et al. 2017a),mayalsobemembersofthe that were placed in CTAB buffer and stored at − 20 °C. Mucoromycotina rather than Glomeromycotina (Orchard Liverwort sections were used for sequencing the 18S ribo- et al. 2017b; Walker et al. 2018). Therefore, our understanding somal RNA gene of Mucoromycotina fungi. This gene was of the host range of Mucoromycotina across land plants and selected as it is the norm for investigating Mucoromycotina in appreciation of their potential significance in modern ecosys- plants (Bidartondo et al. 2011; Desirò et al. 2013; Rimington tems is expanding rapidly. et al. 2015) and allows comparison with previous studies. The Here, we present a worldwide analysis of symbiotic advantages and disadvantages of molecular detection using Mucoromycotina associating with liverworts—the the 18S for endomycorrhizas have been reviewed by Öpik Haplomitriopsida, Marchantiopsida