Biology subjects

Kasson, M. T.

Publications and source records attributed to Kasson, M. T..

10 recordsLinked to original sources

bioRxiv2025

Two morphologically distinct formae speciales in Neonectria magnoliae differ in their virulence on Magnolia family hosts Liriodendron tulipifera and Magnolia fraseri

The family Nectriaceae includes numerous phytopathogenic fungal genera that cause canker diseases on both angiosperm and conifer hosts worldwide. Among these, Neonectria species are globally important canker pathogens of numerous hosts, but their roles in contributing to forest decline and mortality outside their role in beech bark disease and apple canker are largely understudied. In the U.S., Neonectria magnoliae causes perennial cankers on two native hosts in central Appalachia: Fraser magnolia (Magnolia fraseri) and tulip-poplar (Liriodendron tulipifera) and has been recently confirmed from non-native star magnolia (Magnolia stellata) in West Virginia. Both native hosts occur in the central Appalachian Mountains, but Fraser magnolia occurs mostly at higher elevations. Neonectria magnoliae was first described in 1943, yet its impact across the forested landscape remains unclear. To clarify host-specific differences across the contemporary range of Neonectria magnoliae, we used multi-locus phylogenetics, comparative pathogenicity / virulence assays, and morphological analyses to determine if N. magnoliae represents two cryptic species that specialize on tulip-poplar and magnolia, or if N. magnoliae has host-specific pathotypes. Our studies revealed two morphologically distinct formae speciales within N. magnoliae: 1) Neonectria magnoliae f. sp. liriodendri; strains originating from tulip-poplar with increased virulence on this host and lacking macroconidia production and 2) Neonectria magnoliae f. sp. magnoliae; strains originating from Fraser magnolia with increased virulence on this host and producing macroconidia readily in culture. Overall, the incidence of these two pathotypes indicates that neither pathogen alone poses serious risks to either host but adds to cumulative stresses that both tree species are experiencing in the face of global climate change.

microbiology↗

bioRxiv2023

Signatures of transposon-mediated genome inflation, host specialization, and photoentrainment in Entomophthora muscae and allied entomophthoralean fungi

Despite over a century of observations, the obligate insect parasites within the order Entomophthorales remain poorly characterized at the genetic level. This is in part due to their large genome sizes and difficulty in obtaining sequenceable material. In this manuscript, we leveraged a recently-isolated, laboratory-tractable Entomophthora muscae isolate and improved long-read sequencing to obtain a largely-complete entomophthoralean genome. Our E. muscae assembly is 1.03 Gb, consists of 7,810 contigs and contains 81.3% complete fungal BUSCOs. Using a comparative approach with other available (transcriptomic and genomic) datasets from entomophthoralean fungi, we provide new insight into the biology of these understudied pathogens. We offer a head-to-head comparison of morphological and molecular data for species within the E. muscae species complex. Our findings suggest that substantial taxonomic revision is needed to define species within this group and we provide recommendations for differentiating strains and species in the context of the existing body of E. muscae scientific literature. We show that giant genomes are the norm within Entomophthoraceae owing to extensive, but not recent, Ty3 retrotransposon activity, despite the presence of machinery to defend against transposable elements(RNAi). In addition, we find that E. muscae and its closest allies are enriched for M16A peptidases and possess genes that are likely homologs to the blue-light sensor white-collar 1, a Neurospora crassa gene that has a well-established role in maintaining circadian rhythms. We find that E. muscae has an expanded group of acid-trehalases, consistent with trehalose being the primary sugar component of fly (and insect) hemolymph. We uncover evidence that E. muscae diverged from other entomophthoralean fungi by expansion of existing families, rather than loss of particular domains, and possesses a potentially unique suite of secreted catabolic enzymes, consistent with E. muscaes species-specific, biotrophic lifestyle. Altogether, we provide a genetic and molecular foundation that we hope will provide a platform for the continued study of the unique biology of entomophthoralean fungi.

genomics↗

bioRxiv2022

Conoideocrella luteorostrata (Hypocreales: Claviciptaceae), a potential biocontrol fungus for elongate hemlock scale in United States Christmas tree production areas

The entomopathogenic fungus Conoideocrella luteorostrata (Hypocreales: Clavicipitaceae) has recently been implicated in natural epizootics among exotic elongate hemlock scale (EHS) insects in Fraser fir Christmas tree farms in the eastern U.S. Since 1913, asexual populations of C. luteorostrata have been reported from various plant-feeding Hemiptera in the southeastern U.S., but a thorough morphological and phylogenetic examination of the species, particularly detailed characterization of populations involved in recent epizootics in EHS, are lacking. The recovery of multiple strains of C. luteorostrata from mycosed EHS cadavers collected in Ashe County North Carolina provided an opportunity to conduct pathogenicity assays and morphological and phylogenetic studies to investigate genus- and species-level boundaries among members of the Clavicipitaceae. Pathogenicity assays confirmed C. luteorostrata causes mortality of EHS first instar crawlers, an essential first step in developing C. luteorostrata as a biocontrol. The results of the morphological study failed to recover a sexual stage from EHS cadavers or pure cultures, but revealed conidia aligned with previous measurements of the paecilomyces-like asexual state of C. luteorostrata (6.9 {micro}m x 2.6 {micro}m average), with colony and conidiophore morphology consistent with previously reported observations. Additionally, a hirsutella-like synanamorph of C. luteorostrata was observed for the first time under specific lab conditions. In both a four-locus, 54-taxa Clavicipitaceae-wide phylogenetic analysis including the D1-D2 domains of the nuclear 28S rRNA gene (28S), elongation factor 1 alpha (EF1-), DNA-directed RNA polymerase II subunit 1 (RPB1) and DNA-directed RNA polymerase II subunit 2 (RPB2) and a two-locus, 38-taxa (28S & EF1-) phylogenetic analysis, C. luteorostrata, C. tenuis and C. krungchingensis were resolved as strongly supported monophyletic lineages across all loci and both methods (maximum likelihood & Bayesian inference) of phylogenetic inference with the exception of 28S for C. tenuis. Despite the strong support for individual Conoideocrella species, none of the analyses supported the monophyly of the genus, with the inclusion of Dussiella. Due to the paucity of publicly available RPB1 and RPB2 sequence data for Conoideocrella, EF1- provided superior delimitation of intraspecies groupings for C. luteorostrata and C. tenuis and should be used in future studies. Further development of C. luteorostrata as a biocontrol agent against EHS both in Christmas tree farms and surrounding hemlock forests will require additional surveys across diverse Hemiptera and expanded pathogenicity testing to better understand host range and efficacy of this fungus.

microbiology↗

bioRxiv2022

Ecology drives the observed spectrum of hydrophobin protein diversity across Kingdom Fungi

1.Hydrophobins mediate the interactions between fungi and the elements of their ecosystem via assembly at interfaces serving a wide range of diverse functions. As such, these proteins can be seen as a means by which fungi not only adapt to a pre-existing environment, but also actively participate in the construction of their own ecological niches. Through this lens, we provide an expansive hydrophobin survey across the ecological breadth of Kingdom Fungi and advance the view that hydrophobins are best defined as a generic molecular structure with shared core structural features that accommodate a remarkable diversity of amino acid sequences. We examine the relationship between hydrophobin sequences, fungus phylogeny, and associated ecology from 45 fungal proteomes predicted from genomes spanning eight phyla and more than 25 orders. To capture the full spectrum of the hydrophobin amino acid sequence space mapped by our study, we describe the family as a continuum of overlapping hidden Markov models (HMMs), each HMM representing clusters of sequence similarity spanning existing hydrophobin classes. Overall, our approach uncovered ecology as a major driver of hydrophobin diversification, further expanded the known hydrophobins beyond Dikarya, and uncovered evidence extending the possibilities for their function from exclusively extracellular to include intracellular. In addition, we identified novel core groups of cysteine-rich proteins whose conservation across fungi suggest they play key ecological roles. Together, our work offers an ontological framework that captures the diversity of hydrophobin amino acid sequences and highlights the need to revisit challenging fundamental questions regarding hydrophobins to achieve a mechanistic understanding of their function as emerging from assembly within an ecosystem.

microbiology↗

bioRxiv2020

Morphological and Phylogenetic Resolution of Diplodia corticola and D. quercivora, Emerging Canker Pathogens of Oak (Quercus spp.), in the United States

In Mediterranean Europe and the United States, oak species (Quercus spp.) have been in various states of decline for the past several decades. Several insect pests and pathogens contribute to this decline to varying degrees including Phytophthora cinnamomi, Armillaria spp., various insect defoliators, and additionally in the U.S., the oak wilt pathogen, Bretziella fagacearum. More recently, two emerging canker pathogens, Diplodia corticola (Dc) and Diplodia quercivora (Dq) have been implicated in causing dieback and mortality of oak species in Europe and in several regions in the United States. In 2019, a fungal survey was conducted in the Mid-Atlantic region of the Eastern U.S., including Maryland, Pennsylvania, Virginia, and West Virginia to determine the range and impact of Dc and Dq on forest health within the U.S. A total of 563 oak trees between red and white oak family members were evaluated across 33 forests spanning 18 counties. A total of 32 Diplodia isolates encompassing three Diplodia spp. were recovered from 5,335 total plugs collected from the 13 of 18 sampled counties. Recovered Diplodia species included Dc, Dq, and D. sapinea (Ds), as well as Botryosphaeria dothidea (Bd), a closely related canker pathogen in the Botryosphaeriaceae. Both Dc and Ds were recovered from red and white oak family members, whereas Dq was exclusive to white oak family members and Bd to red oak family members. Of these species, Dc was most frequently isolated followed by Dq, Ds, and Bd. Overall, mortality was relatively low across all sampled counties, indicating that these fungi, at the levels that were detected, are not widely inciting oak decline across the region, but more likely are acting opportunistically when the environment is conducive for disease. In an attempt to better understand the relationships among Dc and potentially their geographic origin(s), a multi-gene phylogenetic study and corresponding morphological study were conducted. A total of 49 Diplodia isolates from Spain, France, Italy, and the U.S. were assessed. Across all isolates and geographic regions, Dc formed a strongly supported monophyletic clade sister to Dq and included two strongly supported subclades, one that included isolates from Spain and California and a second that included isolates from Italy, Maryland, and West Virginia. Both subclades also exhibited overlapping spore measurements. These results support Dc as a cosmopolitan pathogen, native to both Europe and the U.S. with the possibility of secondary introductions.

ecology↗

bioRxiv2020

Resolving host and species boundaries for perithecia-producing nectriaceous fungi across the central Appalachian Mountains

The Nectriaceae contains numerous canker pathogens. Due to scarcity of ascomata on many hosts, comprehensive surveys are lacking. Here we characterize the diversity of perithecia-producing nectriaceous fungi across the central Appalachians. Ten species from twelve hosts were recovered including a novel Corinectria sp. from Picea rubens. Neonectria ditissima and N. faginata were most abundant and associated with Fagus grandifolia with beech bark disease (BBD). N. ditissima was also recovered from additional cankered hardwoods, including previously unreported Acer spicatum, Ilex mucronata, and Sorbus americana. Cross-pathogenicity inoculations of N. ditissima confirmed susceptibility of Acer and Betula spp. Neonectria magnoliae was recovered from cankered Liriodendron tulipifera and Magnolia fraseri and pathogenicity on L. tulipifera was confirmed. Fusarium babinda was consistently recovered from beech with BBD, although its role remains unclear. This survey provides a contemporary snapshot of Nectriaceae diversity across the Appalachian Mountains. The following nomenclatural changes are proposed: Neonectria magnoliae comb. nov.

ecology↗

bioRxiv2020

Characterization of mating type genes in heterothallic Neonectria species with emphasis on N. coccinea, N. ditissima, and N. faginata

Neonectria ditissima and N. faginata are canker pathogens involved in an insect-fungus disease complex of American beech (Fagus grandifolia) commonly known as beech bark disease (BBD). In Europe, both N. ditissima and N. coccinea are involved in BBD on European beech (Fagus sylvatica). Field observations across the range of BBD indicate that new infections occur primarily via ascospores. Both heterothallic (self-sterile) and homothallic (self-fertile) mating strategies have been reported for Neonectria fungi. As such, investigations into mating strategy are important for understanding both the disease cycle and population genetics of Neonectria. This is particularly important in the U.S. given that over time N. faginata dominates the BBD pathosystem despite high densities of non-beech hosts for N. ditissima. This study utilized whole-genome sequences of BBD-associated Neonectria spp. along with other publicly available Neonectria and Corinectria genomes and in vitro mating assays to characterize mating type (MAT) loci and confirm thallism for select members of Neonectria and Corinectria. MAT gene-specific primer pairs were developed to efficiently characterize the mating types of additional single ascospore strains of N. ditissima, N. faginata, and N. coccinea and several other related species lacking genomic data. In vitro mating assays were used in combination with molecular results to confirm thallism. These assays also comfirmed the sexual compatibility among N. ditissima strains from different plant hosts. Maximum likelihood phylogenetic analysis of both MAT1-1-1 and MAT1-2-1 sequences recovered trees with similar topology to previously published phylogenies of Neonectria and Corinectria. The results of this study indicate that all Neonectria and Corinectria tested are heterothallic based on our limited sampling and, as such, thallism cannot help explain the inevitable dominance of N. faginata in the BBD pathosystem.

microbiology↗

bioRxiv2019

Evolutionary relationships among Massospora spp. (Entomophthorales), obligate pathogens of cicadas

The fungal genus Massospora (Zoopagomycota: Entomophthorales) includes more than a dozen obligate, sexually transmissible pathogenic species that infect cicadas (Hemiptera) worldwide. At least two species are known to produce psychoactive compounds during infection, which has garnered considerable interest for this enigmatic genus. As with many Entomophthorales, the evolutionary relationships and host associations of Massospora spp. are not well understood. The acquisition of M. diceroproctae from Arizona, M. tettigatis from Chile, and M. platypediae from California and Colorado provided an opportunity to conduct molecular phylogenetic analyses and morphological studies to investigate if these fungi represent a monophyletic group and delimit species boundaries. In a three-locus phylogenetic analysis including the D1-D2 domains of the nuclear 28S rRNA gene (28S), elongation factor 1 alpha-like (EFL), and beta-tubulin (BTUB), Massospora was resolved in a strongly supported monophyletic group containing four well-supported genealogically exclusive lineages, based on two of three methods of phylogenetic inference. There was incongruence among the single-gene trees: two methods of phylogenetic inference recovered trees with either the same topology as the 3-gene concatenated tree (EFL), or a basal polytomy (28S, BTUB). Massospora levispora and M. platypediae isolates formed a single lineage in all analyses and are synonymized here as M. levispora. Massospora diceroproctae was sister to M. cicadina in all three single-gene trees and on an extremely long branch relative to the other Massospora, and even the outgroup taxa, which may reflect an accelerated rate of molecular evolution and/or incomplete taxa sampling. The results of the morphological study presented here indicate that spore measurements may not be phylogenetically or diagnostically informative. Despite recent advances in understanding the ecology of Massospora, much about its host range and diversity remains unexplored. The emerging phylogenetic framework can provide a foundation for exploring co-evolutionary relationships with cicada hosts and the evolution of behavior-altering compounds.

microbiology↗

bioRxiv2019

Diversity and function of fungi associated with the fungivorous millipede, Brachycybe lecontii

Fungivorous millipedes (subterclass Colobognatha) likely represent some of the earliest known mycophagous terrestrial arthropods, yet their fungal partners remain elusive. Here we describe relationships between fungi and the fungivorous millipede, Brachycybe lecontii. Their fungal community is surprisingly diverse with 176 genera, 39 orders, and four phyla and includes several undescribed species. Of particular interest are twelve genera conserved across wood substrates and millipede clades that comprise the core fungal community of B. lecontii. Wood decay fungi, long speculated to serve as the primary food source for Brachycybe species, were absent from this core assemblage and proved lethal to millipedes in pathogenicity assays while entomopathogenic Hypocreales were more common in the core but had little effect on millipede health. This study represents the first survey of fungal communities associated with any colobognath millipede, and these results offer a glimpse into the complexity of millipede fungal communities.

microbiology↗

bioRxiv2018

Discovery of psychoactive plant and mushroom alkaloids in ancient fungal cicada pathogens

Entomopathogenic fungi routinely kill their hosts before releasing infectious spores, but select species keep insects alive while sporulating, which enhances dispersal. Transcriptomics and metabolomics studies of entomopathogens with post-mortem dissemination from their parasitized hosts have unraveled infection processes and host responses, yet mechanisms underlying active spore transmission by Entomophthoralean fungi in living insects remain elusive. Here we report the discovery, through metabolomics, of the plant-associated amphetamine, cathinone, in four Massospora cicadina-infected periodical cicada populations, and the mushroom-associated tryptamine, psilocybin, in annual cicadas infected with Massospora platypediae or Massospora levispora, which appear to represent a single fungal species. The absence of some fungal enzymes necessary for cathinone and psilocybin biosynthesis along with the inability to detect intermediate metabolites or gene orthologs are consistent with possibly novel biosynthesis pathways in Massospora. The neurogenic activities of these compounds suggest the extended phenotype of Massospora that modifies cicada behavior to maximize dissemination is chemically-induced.

ecology↗