Assessing the performance of single-copy genes for recovering robust phylogenies

Whole-genome sequencing and evolutionary analysis of the wild edible mushroom, Morchella eohespera

Morels (Morchella, Ascomycota) are an extremely desired group of edible mushrooms with worldwide distribution. Morchella eohespera is a typical black morel species, belonging to the Elata clade of Morchella species. The biological and genetic studies of this mushroom are rare, largely hindering the studies of molecular breeding and evolutionary aspects. In this study, we performed de novo sequencing and assembly of the M. eohespera strain m200 genome using the third-generation nanopore sequencing platform. The whole-genome size of M. eohespera was 53.81 Mb with a contig N50 of 1.93 Mb, and the GC content was 47.70%. A total of 9,189 protein-coding genes were annotated. Molecular dating showed that M. eohespera differentiated from its relative M. conica at ~19.03 Mya (million years ago) in Burdigalian. Evolutionary analysis showed that 657 gene families were contracted and 244 gene families expanded in M. eohespera versus the related morel species. The non-coding RNA prediction results showed that there were 336 tRNAs, 76 rRNAs, and 45 snRNAs in the M. eohespera genome. Interestingly, there was a high degree of repetition (20.93%) in the M. eohespera genome, and the sizes of long interspersed nuclear elements, short interspersed nuclear elements, and long terminal repeats were 0.83 Mb, 0.009 Mb, and 4.56 Mb, respectively. Additionally, selection pressure analysis identified that a total of 492 genes in the M. eohespera genome have undergone signatures of positive selection. The results of this study provide new insights into the genome evolution of M. eohespera and lay the foundation for in-depth research into the molecular biology of the genus Morchella in the future.

Impact of Dietary Regime and Seasonality on Hindgut's Mycobiota Diversity in Dairy Cows

We describe and discuss the intestinal mycobiota of dairy cows reared in France following variations in dietary regimes and two seasons. Two groups of 21 animals were followed over a summer and winter period, and another group of 28 animals was followed only during the same summer season. The summer diet was based on grazing supplemented with 3-5 kg/d of maize, grass silage and hay, while the winter diet consisted of 30% maize silage, 25% grass silage, 15% hay and 30% concentrate. A total of 69 DNA samples were extracted from the feces of these cows. Amplification and sequencing of the ITS2 region were used to assess mycobiota diversity. Analyses of alpha and beta diversity were performed and compared statistically. The mycobiota changed significantly from summer to winter conditions with a decrease in its diversity, richness and evenness parameters, while beta diversity analysis showed different mycobiota profiles. Of note, the Geotrichum operational taxonomic unit (OTU) was prevalent in the winter group, with a mean relative abundance (RA) of 65% of the total mycobiota. This Geotrichum OTU was also found in the summer group, but to a lesser extent (5%). In conclusion, a summer grazing diet allowed a higher fecal fungal diversity. These data show, for the first time, that a change in diet associated with seasonality plays a central role in shaping hindgut fungal diversity.

Uncovering the Biotechnological Importance of Geotrichum candidum

Fungi make a fundamental contribution to several biotechnological processes, including brewing, winemaking, and the production of enzymes, organic acids, alcohols, antibiotics, and pharmaceuticals. The present review explores the biotechnological importance of the filamentous yeast-like fungus Geotrichum candidum, a ubiquitous species known for its use as a starter in the dairy industry. To uncover G. candidum's biotechnological role, we performed a search for related work through the scientific indexing internet services, Web of Science and Google Scholar. The following query was used: Geotrichum candidum, producing about 6500 scientific papers from 2017 to 2022. From these, approximately 150 that were associated with industrial applications of G. candidum were selected. Our analysis revealed that apart from its role as a starter in the dairy and brewing industries, this species has been administered as a probiotic nutritional supplement in fish, indicating improvements in developmental and immunological parameters. Strains of this species produce a plethora of biotechnologically important enzymes, including cellulases, β-glucanases, xylanases, lipases, proteases, and α-amylases. Moreover, strains that produce antimicrobial compounds and that are capable of bioremediation were identified. The findings of the present review demonstrate the importance of G. candidum for agrifood- and bio-industries and provide further insights into its potential future biotechnological roles.

The DNA replication protein Orc1 from the yeast Torulaspora delbrueckii is required for heterochromatin formation but not as a silencer-binding protein

To understand the process by which new protein functions emerge, we examined how the yeast heterochromatin protein Sir3 arose through gene duplication from the conserved DNA replication protein Orc1. Orc1 is a subunit of the origin recognition complex (ORC), which marks origins of DNA replication. In Saccharomyces cerevisiae, Orc1 also promotes heterochromatin assembly by recruiting the structural proteins Sir1-4 to silencer DNA. In contrast, the paralog of Orc1, Sir3, is a nucleosome-binding protein that spreads across heterochromatic loci in conjunction with other Sir proteins. We previously found that a non-duplicated Orc1 from the yeast Kluyveromyces lactis behaved like ScSir3 but did not have a silencer-binding function like ScOrc1. Moreover, K. lactis lacks Sir1, the protein that interacts directly with ScOrc1 at the silencer. Here, we examined whether the emergence of Sir1 coincided with Orc1 acting as a silencer-binding protein. In the non-duplicated species Torulaspora delbrueckii, which has an ortholog of Sir1 (TdKos3), we found that TdOrc1 spreads across heterochromatic loci independently of ORC, as ScSir3 and KlOrc1 do. This spreading is dependent on the nucleosome binding BAH domain of Orc1 and on Sir2 and Kos3. However, TdOrc1 does not have a silencer-binding function: T. delbrueckii silencers do not require ORC binding sites to function, and Orc1 and Kos3 do not appear to interact. Instead, Orc1 and Kos3 both spread across heterochromatic loci with other Sir proteins. Thus, Orc1 and Sir1/Kos3 originally had different roles in heterochromatin formation than they do now in S. cerevisiae.

Alignment-Free Analysis of Whole-Genome Sequences From Symbiodiniaceae Reveals Different Phylogenetic Signals in Distinct Regions

Dinoflagellates of the family Symbiodiniaceae are predominantly essential symbionts of corals and other marine organisms. Recent research reveals extensive genome sequence divergence among Symbiodiniaceae taxa and high phylogenetic diversity hidden behind subtly different cell morphologies. Using an alignment-free phylogenetic approach based on sub-sequences of fixed length k (i.e. k-mers), we assessed the phylogenetic signal among whole-genome sequences from 16 Symbiodiniaceae taxa (including the genera of Symbiodinium, Breviolum, Cladocopium, Durusdinium and Fugacium) and two strains of Polarella glacialis as outgroup. Based on phylogenetic trees inferred from k-mers in distinct genomic regions (i.e. repeat-masked genome sequences, protein-coding sequences, introns and repeats) and in protein sequences, the phylogenetic signal associated with protein-coding DNA and the encoded amino acids is largely consistent with the Symbiodiniaceae phylogeny based on established markers, such as large subunit rRNA. The other genome sequences (introns and repeats) exhibit distinct phylogenetic signals, supporting the expected differential evolutionary pressure acting on these regions. Our analysis of conserved core k-mers revealed the prevalence of conserved k-mers (>95% core 23-mers among all 18 genomes) in annotated repeats and non-genic regions of the genomes. We observed 180 distinct repeat types that are significantly enriched in genomes of the symbiotic versus free-living Symbiodinium taxa, suggesting an enhanced activity of transposable elements linked to the symbiotic lifestyle. We provide evidence that representation of alignment-free phylogenies as dynamic networks enhances the ability to generate new hypotheses about genome evolution in Symbiodiniaceae. These results demonstrate the potential of alignment-free phylogenetic methods as a scalable approach for inferring comprehensive, unbiased whole-genome phylogenies of dinoflagellates and more broadly of microbial eukaryotes.

Phylogenomic Subsampling and the Search for Phylogenetically Reliable Loci

Phylogenomic subsampling is a procedure by which small sets of loci are selected from large genome-scale data sets and used for phylogenetic inference. This step is often motivated by either computational limitations associated with the use of complex inference methods or as a means of testing the robustness of phylogenetic results by discarding loci that are deemed potentially misleading. Although many alternative methods of phylogenomic subsampling have been proposed, little effort has gone into comparing their behavior across different data sets. Here, I calculate multiple gene properties for a range of phylogenomic data sets spanning animal, fungal, and plant clades, uncovering a remarkable predictability in their patterns of covariance. I also show how these patterns provide a means for ordering loci by both their rate of evolution and their relative phylogenetic usefulness. This method of retrieving phylogenetically useful loci is found to be among the top performing when compared with alternative subsampling protocols. Relatively common approaches such as minimizing potential sources of systematic bias or increasing the clock-likeness of the data are found to fare worse than selecting loci at random. Likewise, the general utility of rate-based subsampling is found to be limited: loci evolving at both low and high rates are among the least effective, and even those evolving at optimal rates can still widely differ in usefulness. This study shows that many common subsampling approaches introduce unintended effects in off-target gene properties and proposes an alternative multivariate method that simultaneously optimizes phylogenetic signal while controlling for known sources of bias.

Phylogenomic Subsampling and the Search for Phylogenetically Reliable Loci

Phylogenomic subsampling is a procedure by which small sets of loci are selected from large genome-scale data sets and used for phylogenetic inference. This step is often motivated by either computational limitations associated with the use of complex inference methods or as a means of testing the robustness of phylogenetic results by discarding loci that are deemed potentially misleading. Although many alternative methods of phylogenomic subsampling have been proposed, little effort has gone into comparing their behavior across different data sets. Here, I calculate multiple gene properties for a range of phylogenomic data sets spanning animal, fungal, and plant clades, uncovering a remarkable predictability in their patterns of covariance. I also show how these patterns provide a means for ordering loci by both their rate of evolution and their relative phylogenetic usefulness. This method of retrieving phylogenetically useful loci is found to be among the top performing when compared with alternative subsampling protocols. Relatively common approaches such as minimizing potential sources of systematic bias or increasing the clock-likeness of the data are found to fare worse than selecting loci at random. Likewise, the general utility of rate-based subsampling is found to be limited: loci evolving at both low and high rates are among the least effective, and even those evolving at optimal rates can still widely differ in usefulness. This study shows that many common subsampling approaches introduce unintended effects in off-target gene properties and proposes an alternative multivariate method that simultaneously optimizes phylogenetic signal while controlling for known sources of bias.

Genome-Scale Profiling Reveals Noncoding Loci Carry Higher Proportions of Concordant Data

Many evolutionary relationships remain controversial despite whole-genome sequencing data. These controversies arise, in part, due to challenges associated with accurately modeling the complex phylogenetic signal coming from genomic regions experiencing distinct evolutionary forces. Here, we examine how different regions of the genome support or contradict well-established relationships among three mammal groups using millions of orthologous parsimony-informative biallelic sites (PIBS) distributed across primate, rodent, and Pecora genomes. We compared PIBS concordance percentages among locus types (e.g. coding sequences (CDS), introns, intergenic regions), and contrasted PIBS utility over evolutionary timescales. Sites derived from noncoding sequences provided more data and proportionally more concordant sites compared with those from CDS in all clades. CDS PIBS were also predominant drivers of tree incongruence in two cases of topological conflict. PIBS derived from most locus types provided surprisingly consistent support for splitting events spread across the timescales we examined, although we find evidence that CDS and intronic PIBS may, respectively and to a limited degree, inform disproportionately about older and younger splits. In this era of accessible wholegenome sequence data, these results:1) suggest benefits to more intentionally focusing on noncoding loci as robust data for tree inference and 2) reinforce the importance of accurate modeling, especially when using CDS data.

Evolutionary Rate Variation Among Lineages in Gene Trees has a Negative Impact on Species-Tree Inference

Phylogenetic analyses of genomic data provide a powerful means of reconstructing the evolutionary relationships among organisms, yet such analyses are often hindered by conflicting phylogenetic signals among loci. Identifying the signals that are most influential to species-tree estimation can help to inform the choice of data for phylogenomic analysis. We investigated this in an analysis of 30 phylogenomic data sets. For each data set, we examined the association between several branch-length characteristics of gene trees and the distance between these gene trees and the corresponding species trees. We found that the distance of each gene tree to the species tree inferred from the full data set was positively associated with variation in root-to-tip distances and negatively associated with mean branch support. However, no such associations were found for gene-tree length, a measure of the overall substitution rate at each locus. We further explored the usefulness of the best-performing branch-based characteristics for selecting loci for phylogenomic analyses. We found that loci that yield gene trees with high variation in root-to-tip distances have a disproportionately distant signal of tree topology compared with the complete data sets. These results suggest that rate variation across lineages should be taken into consideration when exploring and even selecting loci for phylogenomic analysis.[Branch support; data filtering; nucleotide substitution model; phylogenomics; substitution rate; summary coalescent methods.]

Conservation of a DNA Replication Motif among Phylogenetically Distant Budding Yeast Species

Eukaryotic DNA replication begins at genomic loci termed origins, which are bound by the origin recognition complex (ORC). Although ORC is conserved across species, the sequence composition of origins is more varied. In the budding yeast Saccharomyces cerevisiae, the ORC-binding motif consists of an A/T-rich 17 bp “extended ACS” sequence adjacent to a B1 element composed of two 3-bp motifs. Similar sequences occur at origins in closely related species, but it is not clear when this type of replication origin arose and whether it predated a whole-genome duplication that occurred around 100 Ma in the budding yeast lineage. To address these questions, we identified the ORC-binding sequences in the nonduplicated species Torulaspora delbrueckii. We used chromatin immunoprecipitation followed by sequencing and identified 190 ORC-binding sites distributed across the eight T. delbrueckii chromosomes. Using these sites, we identified an ORC-binding motif that is nearly identical to the known motif in S. cerevisiae. We also found that the T. delbrueckii ORC-binding sites function as origins in T. delbrueckii when cloned onto a plasmid and that the motif is required for plasmid replication. Finally, we compared an S. cerevisiae origin with two T. delbrueckii ORC-binding sites and found that they conferred similar stabilities to a plasmid. These results reveal that the ORC-binding motif arose prior to the whole-genome duplication and has been maintained for over 100 Myr.

The wall lizards of the Balkan peninsula: Tackling questions at the interface of phylogenomics and population genomics

Wall lizards of the genus Podarcis (Sauria, Lacertidae) are the predominant reptile group in southern Europe, including 24 recognized species. Mitochondrial DNA data have shown that, with the exception of P. muralis, the Podarcis species distributed in the Balkan peninsula form a species group that is further sub-divided into two subgroups: the one of "P. tauricus" consisting of P. tauricus, P. milensis, P. gaigeae, and P. melisellensis, and the other of "P. erhardii" comprising P. erhardii, P. levendis, P. cretensis, and P. peloponnesiacus. In an attempt to explore the Balkan Podarcis phylogenomic relationships, assess the levels of genetic structure and to re-evaluate the number of extant species, we employed phylogenomic and admixture approaches on ddRADseq (double digested Restriction site Associated DNA sequencing) genomic data. With this efficient Next Generation Sequencing approach, we were able to obtain a large number of genomic loci randomly distributed throughout the genome and use them to resolve the previously obscure phylogenetic relationships among the different Podarcis species distributed in the Balkans. The obtained phylogenomic relationships support the monophyly of both aforementioned subgroups and revealed several divergent lineages within each subgroup, stressing the need for taxonomic re-evaluation of Podarcis' species in Balkans. The phylogenomic trees and the species delimitation analyses confirmed all recently recognized species (P. levendis, P. cretensis, and P. ionicus) and showed the presence of at least two more species, one in P. erhardii and the other in P. peloponnesiacus.

African Arowana Genome Provides Insights on Ancient Teleost Evolution

Osteoglossiformes is a basal clade of teleost, evolving since the Jurassic period. The genomes of Osteoglossiformes species would shed light on the evolution and adaptation of teleost. Here, we established a chromosome-level genome of African arowana. Together with the genomes of pirarucu and Asian arowana, we found that they diverged at ∼106.1 million years ago (MYA) and ∼59.2 MYA, respectively, which are coincident with continental separation. Interestingly, we identified a dynamic genome evolution characterized by a fast evolutionary rate and a high pseudogenization rate in African arowana and pirarucu. Additionally, more transposable elements were found in Asian arowana which confer more gene duplications. Moreover, we found the contraction of olfactory receptor and the expansion of UGT in African arowana might be related to its transformation from carnivore to be omnivore. Taken together, we provided valuable genomic resource of Osteoglossidae and revealed the correlation of biogeography and teleost evolution.

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An evolutionary model of Osteoglossidae along the continental drift is provided

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A faster evolving rate of African arowana than Asian arowana is revealed

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The gene duplications of Asian arowana are related to more class I TE insertions

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A mechanism of African arowana’s feeding habits transition is proposed.

The genetic factors of bilaterian evolution

The Cambrian explosion was a unique animal radiation ~540 million years ago that produced the full range of body plans across bilaterians. The genetic mechanisms underlying these events are unknown, leaving a fundamental question in evolutionary biology unanswered. Using large-scale comparative genomics and advanced orthology evaluation techniques, we identified 157 bilaterian-specific genes. They include the entire Nodal pathway, a key regulator of mesoderm development and left-right axis specification; components for nervous system development, including a suite of G-protein-coupled receptors that control physiology and behaviour, the Robo-Slit midline repulsion system, and the neurotrophin signalling system; a high number of zinc finger transcription factors; and novel factors that previously escaped attention. Contradicting the current view, our study reveals that genes with bilaterian origin are robustly associated with key features in extant bilaterians, suggesting a causal relationship.

The Helvella corium species aggregate in Nordic countries - phylogeny and species delimitation

Mycologists have always been curious about the elaborate morphotypes and shapes of species of the genus Helvella. The small, black, cupulate Helvella specimens have mostly been assigned to Helvella corium, a broadly defined morpho-species. Recent phylogenetic analyses, however, have revealed an aggregate of species hidden under this name. We performed a multispecies coalescent analysis to re-assess species limits and evolutionary relationships of the Helvella corium species aggregate in the Nordic countries. To achieve this, we used morphology and phylogenetic evidence from five loci – heat shock protein 90 (hsp), translation elongation factor 1-alpha (tef), RNA polymerase II (rpb2), and the 5.8S and large subunit (LSU) of the nuclear ribosomal DNA. All specimens under the name Helvella corium in the larger university fungaria of Norway, Sweden and Denmark were examined and barcoded, using partial hsp and/or rpb2 as the preferential secondary barcodes in Helvella. Additional fresh specimens were collected in three years (2015–2018) to obtain in vivo morphological data to aid in species discrimination. The H. corium species aggregate consists of seven phylogenetically distinct species, nested in three divergent lineages, i.e. H. corium, H. alpina and H. pseudoalpina sp. nov. in the /alpina-corium lineage, H. alpestris, H. macrosperma and H. nannfeldtii in the /alpestris-nannfeldtii lineage, and H. alpicola as a weakly supported sister to the /alpestris-nannfeldtii lineage. Among the seven species, the ribosomal loci expressed substantial variation in evolutionary rates, suggesting care in the use of these regions alone in delimitation of Helvella species. Altogether, 469 out of 496 available fungarium specimens were successfully barcoded.

Genome-based classification of Burkholderia cepacia complex provides new insight into its taxonomic status

Background

Accurate classification of different Burkholderia cepacia complex (BCC) species is essential for therapy, prognosis assessment and research. The taxonomic status of BCC remains problematic and an improved knowledge about the classification of BCC is in particular needed.

Methods

We compared phylogenetic trees of BCC based on 16S rRNA, recA, hisA and MLSA (multilocus sequence analysis). Using the available whole genome sequences of BCC, we inferred a species tree based on estimated single-copy orthologous genes and demarcated species of BCC using dDDH/ANI clustering.

Results

We showed that 16S rRNA, recA, hisA and MLSA have limited resolutions in the taxonomic study of closely related bacteria such as BCC. Our estimated species tree and dDDH/ANI clustering clearly separated 116 BCC strains into 36 clusters. With the appropriate reclassification of misidentified strains, these clusters corresponded to 22 known species as well as 14 putative novel species.

Conclusions

This is the first large-scale and systematic study of the taxonomic status of the BCC and could contribute to further insights into BCC taxonomy. Our study suggested that conjunctive use of core phylogeny based on single-copy orthologous genes, as well as pangenome-based dDDH/ANI clustering would provide a preferable framework for demarcating closely related species.

Reviewer

This article was reviewed by Dr. Xianwen Ren.

Fast and reliable molecular methods to detect fungal pathogens in woody plants

Plant diseases caused by pathogenic microorganisms represent a serious threat to plant productivity, food security, and natural ecosystems. An effective framework for early warning and rapid response is a crucial element to mitigate or prevent the impacts of biological invasions of plant pathogens. For these reasons, detection tools play an important role in monitoring plant health, surveillance, and quantitative pathogen risk assessment, thus improving best practices to mitigate and prevent microbial threats. The need to reduce the time of diagnosis has prompted plant pathologists to move towards more sensitive and rapid methods such as molecular techniques. Considering prevention to be the best strategy to protect plants from diseases, this review focuses on fast and reliable molecular methods to detect the presence of woody plant pathogens at early stage of disease development before symptoms occur in the host. A harmonized pool of novel technical, methodological, and conceptual solutions is needed to prevent entry and establishment of new diseases in a country and mitigate the impact of both invasive and indigenous organisms to agricultural and forest ecosystem biodiversity and productivity.

Model Choice, Missing Data, and Taxon Sampling Impact Phylogenomic Inference of Deep Basidiomycota Relationships

Resolving deep divergences in the tree of life is challenging even for analyses of genome-scale phylogenetic data sets. Relationships between Basidiomycota subphyla, the rusts and allies (Pucciniomycotina), smuts and allies (Ustilaginomycotina), and mushroom-forming fungi and allies (Agaricomycotina) were found particularly recalcitrant both to traditional multigene and genome-scale phylogenetics. Here, we address basal Basidiomycota relationships using concatenated and gene tree-based analyses of various phylogenomic data sets to examine the contribution of several potential sources of bias. We evaluate the contribution of biological causes (hard polytomy, incomplete lineage sorting) versus unmodeled evolutionary processes and factors that exacerbate their effects (e.g., fast-evolving sites and long-branch taxa) to inferences of basal Basidiomycota relationships. Bayesian Markov Chain Monte Carlo and likelihood mapping analyses reject the hard polytomy with confidence. In concatenated analyses, fast-evolving sites and oversimplified models of amino acid substitution favored the grouping of smuts with mushroom-forming fungi, often leading to maximal bootstrap support in both concatenation and coalescent analyses. On the contrary, the most conserved data subsets grouped rusts and allies with mushroom-forming fungi, although this relationship proved labile, sensitive to model choice, to different data subsets and to missing data. Excluding putative long-branch taxa, genes with high proportions of missing data and/or with strong signal failed to reveal a consistent trend toward one or the other topology, suggesting that additional sources of conflict are at play. While concatenated analyses yielded strong but conflicting support, individual gene trees mostly provided poor support for any resolution of rusts, smuts, and mushroom-forming fungi, suggesting that the true Basidiomycota tree might be in a part of tree space that is difficult to access using both concatenation and gene tree-based approaches. Inference-based assessments of absolute model fit strongly reject best-fit models for the vast majority of genes, indicating a poor fit of even the most commonly used models. While this is consistent with previous assessments of site-homogenous models of amino acid evolution, this does not appear to be the sole source of confounding signal. Our analyses suggest that topologies uniting smuts with mushroom-forming fungi can arise as a result of inappropriate modeling of amino acid sites that might be prone to systematic bias. We speculate that improved models of sequence evolution could shed more light on basal splits in the Basidiomycota, which, for now, remain unresolved despite the use of whole genome data.

Diversity of Claviceps paspali reveals unknown lineages and unique alkaloid genotypes

Claviceps species affecting Paspalum spp. are a serious problem, as they infect forage grasses such as Paspalum dilatatum and P. plicatulum, producing the ergot disease. The ascomycete C. paspali is known to be the pathogen responsible for this disease in both grasses. This fungus produces alkaloids, including ergot alkaloids and indole-diterpenes, that have potent neurotropic activities in mammals. A total of 32 isolates from Uruguay were obtained from infected P. dilatatum and P. plicatulum. Isolates were phylogenetically identified using partial sequences of the genes coding for the second largest subunit of RNA polymerase subunit II (RPB2), translation elongation factor 1-α (TEF1), β-tubulin (TUB2), and the nuc rDNA 28S subunit (28S). Isolates were also genotyped by randomly amplified polymorphic DNA (RAPD) and presence of genes within the ergot alkaloid (EAS) and indole-diterpene (IDT) biosynthetic gene clusters. This study represents the first genetic characterization of several isolates of C. paspali. The results from this study provide insight into the genetic and genotypic diversity of Claviceps paspali present in P. dilatatum and suggest that isolates from P. plicatulum could be considered an ecological subspecies or specialized variant of C. paspali. Some of these isolates show hypothetical alkaloid genotypes never reported before.

A new species concept for the clinically relevant Mucor circinelloides complex

Mucor species are common soil fungi but also known as agents of human infections (mucormycosis) and used in food production and biotechnology. Mucor circinelloides is the Mucor species that is most frequently isolated from clinical sources. The taxonomy of Mucor circinelloides and its close relatives (Mucor circinelloides complex – MCC) is still based on morphology and mating behaviour. The aim of the present study was a revised taxonomy of the MCC using a polyphasic approach. Using a set of 100 strains molecular phylogenetic analysis of five markers (ITS, rpb1, tsr1, mcm7, and cfs, introduced here) were performed, combined with phenotypic studies, mating tests and the determination of the maximum growth temperatures. The multi-locus analyses revealed 16 phylogenetic species of which 14 showed distinct phenotypical traits and were recognised as discrete species. Five of these species are introduced as novel taxa: M. amethystinus sp. nov., M. atramentarius sp. nov., M. variicolumellatus sp. nov., M. pseudocircinelloides sp. nov., and M. pseudolusitanicus sp. nov. The former formae of M. circinelloides represent one or two separate species. In the MCC, the simple presence of well-shaped zygospores only indicates a close relation of both strains, but not necessarily conspecificity. Seven species of the MCC have been implemented in human infection: M. circinelloides, M. griseocyanus, M. janssenii, M. lusitanicus, M. ramosissimus, M. variicolumellatus, and M. velutinosus.

A Set of Conventional and Multiplex Real-Time PCR Assays for Direct Detection of Elsinoë fawcettii, E. australis, and Pseudocercospora angolensis in Citrus Fruits

Elsinoë fawcettii, E. australis, and Pseudocercospora angolensis are causal agents of citrus scab and spot diseases. The three pathogens are listed as quarantine pests in many countries and are subject to phytosanitary measures to prevent their entry. Diagnosis of these diseases based on visual symptoms is problematic, as they could be confused with other citrus diseases. Isolation of E. fawcettii, E. australis, and P. angolensis from infected tissues is challenging because they grow slowly on culture media. This study developed rapid and specific detection tools for the in planta detection of these pathogens, using either conventional PCR or one-tube multiplex real-time PCR. Primers and hybridization probes were designed to target the single-copy protein-coding gene MS204 for E. fawcettii and E. australis and the translation elongation factor (Tef-1α) gene for P. angolensis. The specificity of the assays was evaluated by testing against DNA extracted from a large number of isolates (102) collected from different citrus-growing areas in the world and from other hosts. The newly described species E. citricola was not included in the specificity test due to its unavailability from the CBS collection. The detection limits of conventional PCR for the three pathogens were 100, 100, and 10 pg μl^-1 gDNA per reaction for E. fawcettii, E. australis, and P. angolensis, respectively. The quadruplex qPCR was fully validated assessing the following performance criteria: sensitivity, specificity, repeatability, reproducibility, and robustness. The quadruplex real-time PCR proved to be highly sensitive, detecting as low as 243, 241, and 242 plasmidic copies (pc) μl^-1 of E. fawcettii, E. australis, and P. angolensis, respectively. Sensitivity and specificity of this quadruplex assay were further confirmed using 176 naturally infected citrus samples collected from Ethiopia, Cameroon, the United States, and Australia. The quadruplex assay developed in this study is robust, cost-effective, and capable of high-throughput detection of the three targets directly from citrus samples. This new detection tool will substantially reduce the turnaround time for reliable species identification and allow rapid response and appropriate action.

Optimal Rates for Phylogenetic Inference and Experimental Design in the Era of Genome-Scale Data Sets

With the rise of genome-scale data sets, there has been a call for increased data scrutiny and careful selection of loci that are appropriate to use in an attempt to resolve a phylogenetic problem. Such loci should maximize phylogenetic information content while minimizing the risk of homoplasy. Theory posits the existence of characters that evolve at an optimum rate, and efforts to determine optimal rates of inference have been a cornerstone of phylogenetic experimental design for over two decades. However, both theoretical and empirical investigations of optimal rates have varied dramatically in their conclusions: spanning no relationship to a tight relationship between the rate of change and phylogenetic utility. Herein, we synthesize these apparently contradictory views, demonstrating both empirical and theoretical conditions under which each is correct. We find that optimal rates of characters-not genes-are generally robust to most experimental design decisions. Moreover, consideration of site rate heterogeneity within a given locus is critical to accurate predictions of utility. Factors such as taxon sampling or the targeted number of characters providing support for a topology are additionally critical to the predictions of phylogenetic utility based on the rate of character change. Further, optimality of rates and predictions of phylogenetic utility are not equivalent, demonstrating the need for further development of comprehensive theory of phylogenetic experimental design. [Divergence time; GC bias; homoplasy; incongruence; information content; internode length; optimal rates; phylogenetic informativeness; phylogenetic theory; phylogenetic utility; phylogenomics; signal and noise; subtending branch length; state space; taxon and character sampling.].

Screening for Exotic Forest Pathogens to Increase Survey Capacity Using Metagenomics

Anthropogenic activities have a major impact on the global environment. Canada's natural resources are threatened by the spread of fungal pathogens, which is facilitated by agricultural practices and international trade. Fungi are introduced to new environments and sometimes become established, in which case they can cause disease outbreaks resulting in extensive forest decline. Here, we describe how a nationwide sample collection strategy coupled to next-generation sequencing (NGS) (i.e., metagenomics) can achieve fast and comprehensive screening for exotic invasive species. This methodology can help provide guidance to phytopathology stakeholders such as regulatory agencies. Several regulated invasive species were monitored by processing field samples collected over 3 years (2013 to 2015) near high-risk areas across Canada. Fifteen sequencing runs were required on the Ion Torrent platform to process 398 samples that yielded 45 million reads. High-throughput screening of fungal and oomycete operational taxonomic units using customized fungi-specific ribosomal internal transcribed spacer 1 barcoded primers was performed. Likewise, Phytophthora-specific barcoded primers were used to amplify the adenosine triphosphate synthase subunit 9-nicotinamide adenine dinucleotide dehydrogenase subunit 9 spacer. Several Phytophthora spp. were detected by NGS and confirmed by species-specific quantitative polymerase chain reaction (qPCR) assays. The target species Heterobasidion annosum sensu stricto could be detected only through metagenomics. We demonstrated that screening target species using a variety of sampling techniques and NGS-the results of which were validated by qPCR-has the potential to increase survey capacity and detection sensitivity, reduce hands-on time and costs, and assist regulatory agencies to identify ports of entry. Considering that early detection and prevention are the keys in mitigating invasive species damage, our method represents a substantial asset in plant pathology management.

Formal description of sequence-based voucherless Fungi: promises and pitfalls, and how to resolve them

There is urgent need for a formal nomenclature of sequence-based, voucherless Fungi, given that environmental sequencing has accumulated more than one billion fungal ITS reads in the Sequence Read Archive, about 1,000 times as many as fungal ITS sequences in GenBank. These unnamed Fungi could help to bridge the gap between 115,000 to 140,000 currently accepted and 2.2 to 3.8 million predicted species, a gap that cannot realistically be filled using specimen or culture-based inventories. The Code never aimed at placing restrictions on the nature of characters chosen for taxonomy, and the requirement for physical types is now becoming a constraint on the advancement of science. We elaborate on the promises and pitfalls of sequence-based nomenclature and provide potential solutions to major concerns of the mycological community. Types of sequence-based taxa, which by default lack a physical specimen or culture, could be designated in four alternative ways: (1) the underlying sample ('bag' type), (2) the DNA extract, (3) fluorescent in situ hybridization (FISH), or (4) the type sequence itself. Only (4) would require changes to the Code and the latter would be the most straightforward approach, complying with three of the five principal functions of types better than physical specimens. A fifth way, representation of the sequence in an illustration, has been ruled as unacceptable in the Code. Potential flaws in sequence data are analogous to flaws in physical types, and artifacts are manageable if a stringent analytical approach is applied. Conceptual errors such as homoplasy, intragenomic variation, gene duplication, hybridization, and horizontal gene transfer, apply to all molecular approaches and cannot be used as a specific argument against sequence-based nomenclature. The potential impact of these phenomena is manageable, as phylogenetic species delimitation has worked satisfactorily in Fungi. The most serious shortcoming of sequence-based nomenclature is the likelihood of parallel classifications, either by describing taxa that already have names based on physical types, or by using different markers to delimit species within the same lineage. The probability of inadvertently establishing sequence-based species that have names available is between 20.4 % and 1.5 % depending on the number of globally predicted fungal species. This compares favourably to a historical error rate of about 30 % based on physical types, and this rate could be reduced to practically zero by adding specific provisions to this approach in the Code. To avoid parallel classifications based on different markers, sequence-based nomenclature should be limited to a single marker, preferably the fungal ITS barcoding marker; this is possible since sequence-based nomenclature does not aim at accurate species delimitation but at naming lineages to generate a reference database, independent of whether these lineages represent species, closely related species complexes, or infraspecies. We argue that clustering methods are inappropriate for sequence-based nomenclature; this approach must instead use phylogenetic methods based on multiple alignments, combined with quantitative species recognition methods. We outline strategies to obtain higher-level phylogenies for ITS-based, voucherless species, including phylogenetic binning, 'hijacking' species delimitation methods, and temporal banding. We conclude that voucherless, sequence-based nomenclature is not a threat to specimen and culture-based fungal taxonomy, but a complementary approach capable of substantially closing the gap between known and predicted fungal diversity, an approach that requires careful work and high skill levels.

Evolutionary history of ergot with a new infrageneric classification (Hypocreales: Clavicipitaceae: Claviceps)

The ergot, genus Claviceps, comprises approximately 60 species of specialised ovarial grass parasites famous for the production of food toxins and pharmaceutics. Although the ergot has been known for centuries, its evolution have not been resolved yet. Our approach combining multilocus phylogeny, molecular dating and the study of ecological, morphological and metabolic features shows that Claviceps originated in South America in the Palaeocene on a common ancestor of BEP (subfamilies Bambusoideae, Ehrhartoideae, Pooideae) and PACMAD (subfamilies Panicoideae, Aristidoideae, Chloridoideae, Micrairoideae, Arundinoideae, Danthonioideae) grasses. Four clades described here as sections diverged during the Paleocene and Eocene. Since Claviceps are parasitic fungi with a close relationship with their host plants, their evolution is influenced by interactions with the new hosts, either by the spread to a new continent or the radiation of the host plants. Three of the sections possess very narrow host ranges and biogeographical distributions and have relatively low toxicity. On the contrary, the section Claviceps, comprising the rye ergot, C. purpurea, is unique in all aspects. Fungi in this section of North American origin have spread all over the world and infect grasses in all subfamilies as well as sedges, and it is the only section synthesising toxic ergopeptines and secalonic acids. The evolutionary success of the Claviceps section members can be explained by high toxin presence, serving as feeding deterrents and playing a role in their protective mutualism with host plants. Closely related taxa Neoclaviceps monostipa and Cepsiclava phalaridis were combined into the genus Aciculosporium.

Molecular detection of airborne Emergomyces africanus, a thermally dimorphic fungal pathogen, in Cape Town, South Africa

Emergomyces africanus is a thermally dimorphic fungus that causes a systemic mycosis in immunocompromised persons in South Africa. Infection is presumed to follow inhalation of airborne propagules. We developed a quantitative PCR protocol able to detect as few as 5 Es. africanus propagules per day. Samples were collected in Cape Town, South Africa over 50 weeks by a Burkard spore trap with an alternate orifice. We detected Es. africanus in air samples from 34 days (10%) distributed over 11 weeks. These results suggest environmental exposure to airborne Es. africanus propagules occurs more commonly in endemic areas than previously appreciated.

Comparative genomics of geographically distant Fusarium fujikuroi isolates revealed two distinct pathotypes correlating with secondary metabolite profiles

Fusarium fujikuroi causes bakanae ("foolish seedling") disease of rice which is characterized by hyper-elongation of seedlings resulting from production of gibberellic acids (GAs) by the fungus. This plant pathogen is also known for production of harmful mycotoxins, such as fusarins, fusaric acid, apicidin F and beauvericin. Recently, we generated the first de novo genome sequence of F. fujikuroi strain IMI 58289 combined with extensive transcriptional, epigenetic, proteomic and chemical product analyses. GA production was shown to provide a selective advantage during infection of the preferred host plant rice. Here, we provide genome sequences of eight additional F. fujikuroi isolates from distant geographic regions. The isolates differ in the size of chromosomes, most likely due to variability of subtelomeric regions, the type of asexual spores (microconidia and/or macroconidia), and the number and expression of secondary metabolite gene clusters. Whilst most of the isolates caused the typical bakanae symptoms, one isolate, B14, caused stunting and early withering of infected seedlings. In contrast to the other isolates, B14 produced no GAs but high amounts of fumonisins during infection on rice. Furthermore, it differed from the other isolates by the presence of three additional polyketide synthase (PKS) genes (PKS40, PKS43, PKS51) and the absence of the F. fujikuroi-specific apicidin F (NRPS31) gene cluster. Analysis of additional field isolates confirmed the strong correlation between the pathotype (bakanae or stunting/withering), and the ability to produce either GAs or fumonisins. Deletion of the fumonisin and fusaric acid-specific PKS genes in B14 reduced the stunting/withering symptoms, whereas deletion of the PKS51 gene resulted in elevated symptom development. Phylogenetic analyses revealed two subclades of F. fujikuroi strains according to their pathotype and secondary metabolite profiles.

How to boost marine fungal research: A first step towards a multidisciplinary approach by combining molecular fungal ecology and natural products chemistry

Marine fungi have attracted attention in recent years due to increased appreciation of their functional role in ecosystems and as important sources of new natural products. The concomitant development of various "omic" technologies has boosted fungal research in the fields of biodiversity, physiological ecology and natural product biosynthesis. Each of these research areas has its own research agenda, scientific language and quality standards, which have so far hindered an interdisciplinary exchange. Inter- and transdisciplinary interactions are, however, vital for: (i) a detailed understanding of the ecological role of marine fungi, (ii) unlocking their hidden potential for natural product discovery, and (iii) designing access routes for biotechnological production. In this review and opinion paper, we describe the two different "worlds" of marine fungal natural product chemists and marine fungal molecular ecologists. The individual scientific approaches and tools employed are summarised and explained, and enriched with a first common glossary. We propose a strategy to find a multidisciplinary approach towards a comprehensive view on marine fungi and their chemical potential.

A synopsis of the saddle fungi (Helvella: Ascomycota) in Europe - species delimitation, taxonomy and typification

Helvella is a widespread, speciose genus of large apothecial ascomycetes (Pezizomycete: Pezizales) that are found in terrestrial biomes of the Northern and Southern Hemispheres. This study represents a beginning on assessing species limits and applying correct names for Helvella species based on type material and specimens in the university herbaria (fungaria) of Copenhagen (C), Harvard (FH) and Oslo (O). We use morphology and phylogenetic evidence from four loci – heat shock protein 90 (hsp), translation elongation factor alpha (tef), RNA polymerase II (rpb2) and the nuclear large subunit ribosomal DNA (LSU) – to assess species boundaries in an expanded sample of Helvella specimens from Europe. We combine the morphological and phylogenetic information from 55 Helvella species from Europe with a small sample of Helvella species from other regions of the world. Little intraspecific variation was detected within the species using these molecular markers; hsp and rpb2 markers provided useful barcodes for species delimitation in this genus, while LSU provided more variable resolution among the pertinent species. We discuss typification issues and identify molecular characteristics for 55 European Helvella species, designate neo- and epitypes for 30 species, and describe seven Helvella species new to science, i.e., H. alpicola, H. alpina, H. carnosa, H. danica, H. nannfeldtii, H. pubescens and H. scyphoides.

The Epichloë festucae antifungal protein has activity against the plant pathogen Sclerotinia homoeocarpa, the causal agent of dollar spot disease

Epichloë spp. are naturally occurring fungal endophytic symbionts of many cool-season grasses. Infection by the fungal endophytes often confers biotic and abiotic stress tolerance to their hosts. Endophyte-mediated disease resistance is well-established in the fine fescue grass Festuca rubra subsp. rubra (strong creeping red fescue) infected with E. festucae. Resistance to fungal pathogens is not an established effect of endophyte infection of other grass species, and may therefore be unique to the fine fescues. The underlying mechanism of the disease resistance is unknown. E. festucae produces a secreted antifungal protein that is highly expressed in the infected plant tissues and may therefore be involved in the disease resistance. Most Epichloë spp. do not have a gene for a similar antifungal protein. Here we report the characterization of the E. festucae antifungal protein, designated Efe-AfpA. The antifungal protein partially purified from the apoplastic proteins of endophyte-infected plant tissue and the recombinant protein expressed in the yeast Pichia pastoris was found to have activity against the important plant pathogen Sclerotinia homoeocarpa. Efe-AfpA may therefore be a component of the disease resistance seen in endophyte-infected strong creeping red fescue.

A new marker sequence for systematics of medically important fungi based on amino acid sequence of the largest subunit of RNA polymerase I

Molecular evolution has dominated taxonomic studies for decades, replacing traditional methods for identification and classification. However, there is a need for better markers to resolve the problems that have limited their usefulness. In this report, we introduce the protein tag (Ptag) sequence, a highly polymorphic amino acid sequence within the C-terminal region of the largest subunit of RNA polymerase I, as a new systematic tag sequence for delineating the evolutionary history of medically important fungi. As Ptag sequences are highly polymorphic between species and low within species, 42 fungal species representing the main taxonomic groups in the phyla Ascomycota and Basidiomycota were tested. The phylogenetic tree inferred from the Ptag sequences showed high consistency with the accepted classification of the Assembling the Fungal Tree of Life (AFTOL) project. Moreover, it could resolve the interspecies phylogenetic relationships of the tested taxa. In contrast, the phylogeny inferred from the nucleotide tag (Ntag) sequence, encoding the Ptag peptide, displayed lesser discriminatory power in resolving the phylogenetic relationships among distantly related taxa. In the case of closely related fungal species, the phylogenetic trees for Ptag and Ntag sequences were consistent with the tree for ITS1 sequences of 11 dermatophytic species. Taken together, the Ptag sequences should contribute to inferring phylogeny among species whereas the Ntag sequences should be useful to analyze variations among closely related species to resolve taxonomic issues in fungi.

A new promising phylogenetic marker to study the diversity of fungal communities: The Glycoside Hydrolase 63 gene

In molecular ecology, the development of efficient molecular markers for fungi remains an important research domain. Nuclear ribosomal internal transcribed spacer (ITS) region was proposed as universal DNA barcode marker for fungi, but this marker was criticized for Indel-induced alignment problems and its potential lack of phylogenetic resolution. Our main aim was to develop a new phylogenetic gene and a putative functional marker, from single-copy gene, to describe fungal diversity. Thus, we developed a series of primers to amplify a polymorphic region of the Glycoside Hydrolase GH63 gene, encoding exo-acting α-glucosidases, in basidiomycetes. These primers were validated on 125 different fungal genomic DNAs, and GH63 amplification yield was compared with that of already published functional markers targeting genes coding for laccases, N-acetylhexosaminidases, cellobiohydrolases and class II peroxidases. Specific amplicons were recovered for 95% of the fungal species tested, and GH63 amplification success was strikingly higher than rates obtained with other functional genes. We downloaded the GH63 sequences from 483 fungal genomes publicly available at the JGI mycocosm database. GH63 was present in 461 fungal genomes belonging to all phyla, except Microsporidia and Neocallimastigomycota divisions. Moreover, the phylogenetic trees built with both GH63 and Rpb1 protein sequences revealed that GH63 is also a promising phylogenetic marker. Finally, a very high proportion of GH63 proteins was predicted to be secreted. This molecular tool could be a new phylogenetic marker of fungal species as well as potential indicator of functional diversity of basidiomycetes fungal communities in term of secretory capacities.

Fungal Identification Using Molecular Tools: A Primer for the Natural Products Research Community

Fungi are morphologically, ecologically, metabolically, and phylogenetically diverse. They are known to produce numerous bioactive molecules, which makes them very useful for natural products researchers in their pursuit of discovering new chemical diversity with agricultural, industrial, and pharmaceutical applications. Despite their importance in natural products chemistry, identification of fungi remains a daunting task for chemists, especially those who do not work with a trained mycologist. The purpose of this review is to update natural products researchers about the tools available for molecular identification of fungi. In particular, we discuss (1) problems of using morphology alone in the identification of fungi to the species level; (2) the three nuclear ribosomal genes most commonly used in fungal identification and the potential advantages and limitations of the ITS region, which is the official DNA barcoding marker for species-level identification of fungi; (3) how to use NCBI-BLAST search for DNA barcoding, with a cautionary note regarding its limitations; (4) the numerous curated molecular databases containing fungal sequences; (5) the various protein-coding genes used to augment or supplant ITS in species-level identification of certain fungal groups; and (6) methods used in the construction of phylogenetic trees from DNA sequences to facilitate fungal species identification. We recommend that, whenever possible, both morphology and molecular data be used for fungal identification. Our goal is that this review will provide a set of standardized procedures for the molecular identification of fungi that can be utilized by the natural products research community.

Increased phylogenetic resolution within the ecologically important Rhizopogon subgenus Amylopogon using 10 anonymous nuclear loci

Rhizopogon species are ecologically significant ectomycorrhizal fungi in conifer ecosystems. The importance of this system merits the development and utilization of a more robust set of molecular markers specifically designed to evaluate their evolutionary ecology. Anonymous nuclear loci (ANL) were developed for R. subgenus Amylopogon. Members of this subgenus occur throughout the United States and are exclusive fungal symbionts associated with Pterospora andromedea, a threatened mycoheterotrophic plant endemic to disjunct eastern and western regions of North America. Candidate ANL were developed from 454 shotgun pyrosequencing and assessed for positive amplification across targeted species, sequencing success, and recovery of phylogenetically informative sites. Ten ANL were successfully developed and were subsequently used to sequence representative taxa, herbaria holotype and paratype specimens in R. subgenus Amylopogon. Phylogenetic reconstructions were performed on individual and concatenated data sets by Bayesian inference and maximum likelihood methods. Phylogenetic analyses of these 10 ANL were compared with a phylogeny traditionally constructed using the universal fungal barcode nuc rDNA ITS1-5.8S-ITS2 region (ITS). The resulting ANL phylogeny was consistent with most of the species designations delineated by ITS. However, the ANL phylogeny provided much greater phylogenetic resolution, yielding new evidence for cryptic species within previously defined species of R. subgenus Amylopogon. Additionally, the rooted ANL phylogeny provided an alternate topology to the ITS phylogeny, which inferred a novel set of evolutionary relationships not identified in prior phylogenetic studies.

Comparative "Omics" of the Fusarium fujikuroi Species Complex Highlights Differences in Genetic Potential and Metabolite Synthesis

Species of the Fusarium fujikuroi species complex (FFC) cause a wide spectrum of often devastating diseases on diverse agricultural crops, including coffee, fig, mango, maize, rice, and sugarcane. Although species within the FFC are difficult to distinguish by morphology, and their genes often share 90% sequence similarity, they can differ in host plant specificity and life style. FFC species can also produce structurally diverse secondary metabolites (SMs), including the mycotoxins fumonisins, fusarins, fusaric acid, and beauvericin, and the phytohormones gibberellins, auxins, and cytokinins. The spectrum of SMs produced can differ among closely related species, suggesting that SMs might be determinants of host specificity. To date, genomes of only a limited number of FFC species have been sequenced. Here, we provide draft genome sequences of three more members of the FFC: a single isolate of F. mangiferae, the cause of mango malformation, and two isolates of F. proliferatum, one a pathogen of maize and the other an orchid endophyte. We compared these genomes to publicly available genome sequences of three other FFC species. The comparisons revealed species-specific and isolate-specific differences in the composition and expression (in vitro and in planta) of genes involved in SM production including those for phytohormome biosynthesis. Such differences have the potential to impact host specificity and, as in the case of F. proliferatum, the pathogenic versus endophytic life style.

A genomic comparison of putative pathogenicity-related gene families in five members of the Ophiostomatales with different lifestyles

Ophiostomatoid fungi are vectored by their bark-beetle associates and colonize different host tree species. To survive and proliferate in the host, they have evolved mechanisms for detoxification and elimination of host defence compounds, efficient nutrient sequestration, and, in pathogenic species, virulence towards plants. Here, we assembled a draft genome of the spruce pathogen Ophiostoma bicolor. For our comparative and phylogenetic analyses, we mined the genomes of closely related species (Ophiostoma piceae, Ophiostoma ulmi, Ophiostoma novo-ulmi, and Grosmannia clavigera). Our aim was to acquire a genomic and evolutionary perspective of gene families important in host colonization. Genome comparisons showed that both the nuclear and mitochondrial genomes in our assembly were largely complete. Our O. bicolor 25.3 Mbp draft genome had 10 018 predicted genes, 6041 proteins with gene ontology (GO) annotation, 269 carbohydrate-active enzymes (CAZymes), 559 peptidases and inhibitors, and 1373 genes likely involved in pathogen-host interactions. Phylogenetic analyses of selected protein families revealed core sets of cytochrome P450 genes, ABC transporters and backbone genes involved in secondary metabolite (SM) biosynthesis (polyketide synthases (PKS) and non-ribosomal synthases), and species-specific gene losses and duplications. Phylogenetic analyses of protein families of interest provided insight into evolutionary adaptations to host biochemistry in ophiostomatoid fungi.

Globally distributed root endophyte Phialocephala subalpina links pathogenic and saprophytic lifestyles

BACKGROUND

Whereas an increasing number of pathogenic and mutualistic ascomycetous species were sequenced in the past decade, species showing a seemingly neutral association such as root endophytes received less attention. In the present study, the genome of Phialocephala subalpina, the most frequent species of the Phialocephala fortinii s.l. - Acephala applanata species complex, was sequenced for insight in the genome structure and gene inventory of these wide-spread root endophytes.

RESULTS

The genome of P. subalpina was sequenced using Roche/454 GS FLX technology and a whole genome shotgun strategy. The assembly resulted in 205 scaffolds and a genome size of 69.7 Mb. The expanded genome size in P. subalpina was not due to the proliferation of transposable elements or other repeats, as is the case with other ascomycetous genomes. Instead, P. subalpina revealed an expanded gene inventory that includes 20,173 gene models. Comparative genome analysis of P. subalpina with 13 ascomycetes shows that P. subalpina uses a versatile gene inventory including genes specific for pathogens and saprophytes. Moreover, the gene inventory for carbohydrate active enzymes (CAZymes) was expanded including genes involved in degradation of biopolymers, such as pectin, hemicellulose, cellulose and lignin.

CONCLUSIONS

The analysis of a globally distributed root endophyte allowed detailed insights in the gene inventory and genome organization of a yet largely neglected group of organisms. We showed that the ubiquitous root endophyte P. subalpina has a broad gene inventory that links pathogenic and saprophytic lifestyles.

Comparative genomics to explore phylogenetic relationship, cryptic sexual potential and host specificity of Rhynchosporium species on grasses

BACKGROUND

The Rhynchosporium species complex consists of hemibiotrophic fungal pathogens specialized to different sweet grass species including the cereal crops barley and rye. A sexual stage has not been described, but several lines of evidence suggest the occurrence of sexual reproduction. Therefore, a comparative genomics approach was carried out to disclose the evolutionary relationship of the species and to identify genes demonstrating the potential for a sexual cycle. Furthermore, due to the evolutionary very young age of the five species currently known, this genus appears to be well-suited to address the question at the molecular level of how pathogenic fungi adapt to their hosts.

RESULTS

The genomes of the different Rhynchosporium species were sequenced, assembled and annotated using ab initio gene predictors trained on several fungal genomes as well as on Rhynchosporium expressed sequence tags. Structures of the rDNA regions and genome-wide single nucleotide polymorphisms provided a hypothesis for intra-genus evolution. Homology screening detected core meiotic genes along with most genes crucial for sexual recombination in ascomycete fungi. In addition, a large number of cell wall-degrading enzymes that is characteristic for hemibiotrophic and necrotrophic fungi infecting monocotyledonous hosts were found. Furthermore, the Rhynchosporium genomes carry a repertoire of genes coding for polyketide synthases and non-ribosomal peptide synthetases. Several of these genes are missing from the genome of the closest sequenced relative, the poplar pathogen Marssonina brunnea, and are possibly involved in adaptation to the grass hosts. Most importantly, six species-specific genes coding for protein effectors were identified in R. commune. Their deletion yielded mutants that grew more vigorously in planta than the wild type.

CONCLUSION

Both cryptic sexuality and secondary metabolites may have contributed to host adaptation. Most importantly, however, the growth-retarding activity of the species-specific effectors suggests that host adaptation of R. commune aims at extending the biotrophic stage at the expense of the necrotrophic stage of pathogenesis. Like other apoplastic fungi Rhynchosporium colonizes the intercellular matrix of host leaves relatively slowly without causing symptoms, reminiscent of the development of endophytic fungi. Rhynchosporium may therefore become an object for studying the mutualism-parasitism transition.

A complete toolset for the study of Ustilago bromivora and Brachypodium sp. as a fungal-temperate grass pathosystem

Due to their economic relevance, the study of plant pathogen interactions is of importance. However, elucidating these interactions and their underlying molecular mechanisms remains challenging since both host and pathogen need to be fully genetically accessible organisms. Here we present milestones in the establishment of a new biotrophic model pathosystem: Ustilago bromivora and Brachypodium sp. We provide a complete toolset, including an annotated fungal genome and methods for genetic manipulation of the fungus and its host plant. This toolset will enable researchers to easily study biotrophic interactions at the molecular level on both the pathogen and the host side. Moreover, our research on the fungal life cycle revealed a mating type bias phenomenon. U. bromivora harbors a haplo-lethal allele that is linked to one mating type region. As a result, the identified mating type bias strongly promotes inbreeding, which we consider to be a potential speciation driver.

Sporadic Gene Loss After Duplication Is Associated with Functional Divergence of Sirtuin Deacetylases Among Candida Yeast Species

Gene duplication promotes the diversification of protein functions in several ways. Ancestral functions can be partitioned between the paralogs, or a new function can arise in one paralog. These processes are generally viewed as unidirectional. However, paralogous proteins often retain related functions and can substitute for one another. Moreover, in the event of gene loss, the remaining paralog might regain ancestral functions that had been shed. To explore this possibility, we focused on the sirtuin deacetylase SIR2 and its homolog HST1 in the CTG clade of yeasts. HST1 has been consistently retained throughout the clade, whereas SIR2 is only present in a subset of species. These NAD⁺-dependent deacetylases generate condensed chromatin that represses transcription and stabilizes tandemly repeated sequences. By analyzing phylogenetic trees and gene order, we found that a single duplication of the SIR2/HST1 gene occurred, likely prior to the emergence of the CTG clade. This ancient duplication was followed by at least two independent losses of SIR2. Functional characterization of Sir2 and Hst1 in three species revealed that these proteins have not maintained consistent functions since the duplication. In particular, the rDNA locus is deacetylated by Sir2 in Candida albicans, by Hst1 in C. lusitaniae, and by neither paralog in C. parapsilosis. In addition, the subtelomeres in C. albicans are deacetylated by Sir2 rather than by Hst1, which is orthologous to the sirtuin associated with Saccharomyces cerevisiae subtelomeres. These differences in function support the model that sirtuin deacetylases can regain ancestral functions to compensate for gene loss.