The Architecture of Metabolism Maximizes Biosynthetic Diversity in the Largest Class Of
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bioRxiv preprint doi: https://doi.org/10.1101/2020.01.31.928846; this version posted February 1, 2020. The copyright holder for this preprint (which was not certified by peer review) is the author/funder. All rights reserved. No reuse allowed without permission. 1 Research Article 2 The architecture of metabolism maximizes biosynthetic diversity in the largest class of 3 fungi 4 Authors: 5 Emile Gluck-Thaler, Department of Plant Pathology, The Ohio State University Columbus, OH, USA, 6 and Biological Sciences, University of Pittsburgh, Pittsburgh, PA, USA 7 Sajeet Haridas, US Department of Energy Joint Genome Institute, Lawrence Berkeley National 8 Laboratory, Berkeley, CA, USA 9 Manfred Binder, TechBase, R-Tech GmbH, Regensburg, Germany 10 Igor V. Grigoriev, US Department of Energy Joint Genome Institute, Lawrence Berkeley National 11 Laboratory, Berkeley, CA, USA, and Department of Plant and Microbial Biology, University of 12 California, Berkeley, CA 13 Pedro W. Crous, Westerdijk Fungal Biodiversity Institute, Uppsalalaan 8, 3584 CT Utrecht, The 14 Netherlands 15 Joseph W. Spatafora, Department of Botany and Plant Pathology, Oregon State University, OR, USA 16 Kathryn Bushley, Department of Plant and Microbial Biology, University of Minnesota, MN, USA 17 Jason C. Slot, Department of Plant Pathology, The Ohio State University Columbus, OH, USA 18 corresponding author: [email protected] 19 1 bioRxiv preprint doi: https://doi.org/10.1101/2020.01.31.928846; this version posted February 1, 2020. The copyright holder for this preprint (which was not certified by peer review) is the author/funder. All rights reserved. No reuse allowed without permission. 19 Abstract: 20 Background - Ecological diversity in fungi is largely defined by metabolic traits, including the 21 ability to produce secondary or "specialized" metabolites (SMs) that mediate interactions with 22 other organisms. Fungal SM pathways are frequently encoded in biosynthetic gene clusters 23 (BGCs), which facilitate the identification and characterization of metabolic pathways. Variation 24 in BGC composition reflects the diversity of their SM products. Recent studies have documented 25 surprising diversity of BGC repertoires among isolates of the same fungal species, yet little is 26 known about how this population-level variation is inherited across macroevolutionary 27 timescales. 28 Results - Here, we applied a novel linkage-based algorithm to reveal previously unexplored 29 dimensions of diversity in BGC composition, distribution, and repertoire across 101 species of 30 Dothideomycetes, which are considered to be the most phylogenetically diverse class of fungi 31 and are known to produce many SMs. We predicted both complementary and overlapping sets of 32 clustered genes compared with existing methods and identified novel gene pairs that associate 33 with known secondary metabolite genes. We found that variation in BGC repertoires is due to 34 non-overlapping BGC combinations and that several BGCs have biased ecological distributions, 35 consistent with niche-specific selection. We observed that total BGC diversity scales linearly 36 with increasing repertoire size, suggesting that secondary metabolites have little structural 37 redundancy in individual fungi. 38 Conclusions - We project that there is substantial unsampled BGC diversity across specific 39 families of Dothideomycetes, which will provide a roadmap for future sampling efforts. Our 40 approach and findings lend new insight into how BGC diversity is generated and maintained 41 across an entire fungal taxonomic class. 2 bioRxiv preprint doi: https://doi.org/10.1101/2020.01.31.928846; this version posted February 1, 2020. The copyright holder for this preprint (which was not certified by peer review) is the author/funder. All rights reserved. No reuse allowed without permission. 42 Keywords: 43 chemical ecology; Fungi; metabolism; gene cluster 44 45 Background: 46 Plants, bacteria and fungi produce the majority of the earth's biochemical diversity. These 47 organisms produce a remarkable variety of secondary/specialized metabolites (SMs) that can 48 mediate ecological functions, including defense, resource acquisition, and mutualism. Standing 49 SM diversity is often high at the population level, which may affect the rates of adaptation over 50 microevolutionary timescales. For example, high intraspecific quantitative and qualitative 51 chemotype diversity in plants can enable rapid adaptation to local biotic factors (Agrawal, 52 Hastings et al. 2012; Züst, Heichinger et al. 2012; Glassmire, Jeffrey et al. 2016). However, the 53 fate of population-level chemodiversity across longer timescales is not well explored in plants or 54 other lineages. We therefore sought to identify how metabolic variation is distributed across 55 macroevolutionary timescales by profiling chemodiversity across a well-sampled taxonomic 56 class. 57 The Dothideomycetes, which originated between 247 and 459 million years ago 58 (Beimforde, Feldberg et al. 2014), comprise the largest and arguably most phylogenetically 59 diverse class of fungi. Currently, 19,000 species are recognized in 32 orders containing more 60 than 1,300 genera (Zhang, Crous et al. 2011). Dothideomycetes are divided into two major 61 subclasses, the Pleosporomycetidae (order Pleosporales) and Dothideomycetidae (orders 62 Dothideales, Capnodiales, and Myriangiales), which correspond to the presence or absence, 63 respectively, of pseudoparaphyses during development of the asci (Schoch, Crous et al. 2009). 64 Several other orders await definitive placement. 3 bioRxiv preprint doi: https://doi.org/10.1101/2020.01.31.928846; this version posted February 1, 2020. The copyright holder for this preprint (which was not certified by peer review) is the author/funder. All rights reserved. No reuse allowed without permission. 65 Dothideomycetes also display a large diversity of fungal lifestyles and ecologies. The 66 majority of Dothideomycetes are terrestrial and associate with phototrophic hosts as either 67 pathogens, saprobes, endophytes (Schoch, Crous et al. 2009), lichens (Nelsen, Lucking et al. 68 2011), or ectomycorrhizal symbionts (Spatafora, Owensby et al. 2012). Six orders contain plant 69 pathogens capable of infecting nearly every known crop species. The Pleosporales and 70 Capnodiales, in particular, are dominated by asexual plant pathogens that cause significant 71 economic losses and have been well sampled in previous genome sequencing efforts (Goodwin, 72 Ben M'Barek et al. 2011; Ohm, Feau et al. 2012; Oliver, Friesen et al. 2012; Condon, Leng et al. 73 2013; Manning, Pandelova et al. 2013). A single order (Jahnulales) contains aquatic, primarily 74 freshwater, species (Suetrong, Boonyuen et al. 2011). Other ecologies include human and animal 75 pathogens, including some taxa that can elicit allergies and asthma (Crameri, Garbani et al. 76 2014), and rock-inhabiting fungi (Ruibal, Gueidan et al. 2009). 77 This broad range of lifestyles is accompanied by extensive diversity of SMs, for which 78 very few have known ecological roles. The Dothideomycetes, and several other ascomycete 79 classes (Eurotiomycetes, Sordariomycetes, and Leotiomycetes), produce the greatest number and 80 diversity of SMs across the fungal kingdom (Spatafora and Bushley 2015; Akimitsu et al. 2014). 81 Economically important plant pathogens in the Pleosporales (Alternaria, Bipolaris, Exserohilum, 82 Leptosphaeria, Pyrenophora, and Stagonospora), in particular, are known to produce host- 83 selective toxins that confer the ability to cause disease in specific plant hosts (Walton and 84 Panaccione 1993; Walton 1996; Wolpert, Dunkle et al. 2002; Ciuffetti, Manning et al. 2010, 85 Pandelova, Figueroa et al. 2012; Akimitsu, Tsuge et al. 2014). Other toxins first identified in 86 Pleosporales have roles in virulence, but are not pathogenicity determinants, including the PKS 87 derived compounds depudecin (Wight, Kim et al. 2009) and solanapyrone (Kaur 1995). 4 bioRxiv preprint doi: https://doi.org/10.1101/2020.01.31.928846; this version posted February 1, 2020. The copyright holder for this preprint (which was not certified by peer review) is the author/funder. All rights reserved. No reuse allowed without permission. 88 Dothideomycetes are also known to produce bioactive metabolites shared with more 89 distantly related fungal classes. Sirodesmin, a virulence factor produced by Leptosphaeria 90 maculans, for example, belongs to the same class of epipolythiodioxopiperazine (ETP) toxins as 91 gliotoxin, an immunosuppressant produced by the eurotiomycete human pathogen Aspergillus 92 fumigatus (Gardiner, Waring et al. 2005; Patron, Waller et al. 2007). Dothistromin, a polyketide 93 metabolite produced by the pine pathogen Dothistroma septosporum shares ancestry with 94 aflatoxin (Bradshaw, Slot et al. 2013), a mycotoxin produced by Aspergillus species that poses 95 serious human health and environmental risks worldwide (Horn 2003; Wang and Tang 2004). 96 A majority of bioactive metabolites in Dothideomycetes are small-molecule SMs that, 97 like those of other fungi, are frequently the products of biosynthetic gene clusters (BGCs) 98 composed of enzymes, transporters, and regulators that contribute to a common SM pathway. 99 Most of these BGCs are defined by four main classes of SM core signature enzymes: 1) 100 nonribosomal peptide synthetases (NRPS), 2) polyketide synthetases (PKS), 3) terpene synthases 101 (TS), and 4) dimethylallyl tryptophan synthases (DMAT) (Hoffmeister & Keller