Ancestral predisposition toward a domesticated lifestyle in the termite-cultivated fungus Termitomyces

The ancestor of termites relied on gut symbionts for degradation of plant material, an association that persists in all termite families. However, the single-lineage Macrotermitinae has additionally acquired a fungal symbiont that complements digestion of food outside the termite gut. Phylogenetic analysis has shown that fungi grown by these termites forma clade—the genus Termitomyces—but the events leading toward domestication remain unclear. To address this, we reconstructed the lifestyle of the common ancestor of Termitomyces using a combination of ecological data with a phylogenomic analysis of 21 related non-domesticated species and 25 species of Termitomyces. We show that the closely related genera Blastosporella and Arthromyces also contain insect-associated species. Furthermore, the genus Arthromyces produces asexual spores on the mycelium, which may facilitate insect dispersal when growing on aggregated subterranean fecal pellets of a plant-feeding insect. The sister-group relationship between Arthromyces and Termitomyces implies that insect association and asexual sporulation, present in both genera, preceded the domestication of Termitomyces and did not follow domestication as has been proposed previously. Specialization of the common ancestor of these two genera on an insect-fecal substrate is further supported by similar carbohydrate-degrading profiles between Arthromyces and Termitomyces. We describe a set of traits that may have predisposed the ancestor of Termitomyces toward domestication, with each trait found scattered in related taxa outside of the termite-domesticated clade. This pattern indicates that the origin of the termite-fungus symbiosis may not have required large-scale changes of the fungal partner.http://www.cell.com/current-biology/homeam2022BiochemistryForestry and Agricultural Biotechnology Institute (FABI)GeneticsMicrobiology and Plant Patholog

An unusual sexual stage in the alkalophilic ascomycete Sodiomyces alkalinus

Exploring life cycles of fungi is insightful for understanding their basic biology and can highlight their ecology. Here, we dissected the sexual and asexual life cycles of the obligate alkalophilic ascomycete Sodiomyces alkalinus that thrives at extremely high pH of soda lakes. S. alkalinus develops acremonium-type asexual sporulation, commonly found in ascomycetous fungi. However, the sexual stage was unusual, featuring very early lysis of asci which release young ascospores inside a fruit body long before its maturation. In a young fruit body, a slimy matrix which originates from the combined epiplasm of asci and united cytoplasm of the pseudoparenchymal cells, surrounds pooled maturing ascospores. Upon maturity, the ascospores are forcibly released through a crack in the fruit body, presumably due to an increased turgor pressure. These features of the sexual stage development resemble the ones found in unrelated marine fungi, indicating convergent evolution of the trait. We hypothesise these developmental features of S. alkalinus to be adaptive in the conditions of periodically inundated rims of soda lakes where the fungus thrives.</p

Somatic deficiency causes reproductive parasitism in a fungus

Some multicellular organisms can fuse because mergers potentially provide mutual benefits. However, experimental evolution in the fungus Neurospora crassa has demonstrated that free fusion of mycelia favours cheater lineages, but the mechanism and evolutionary dynamics of dishonest exploitation are unknown. Here we show, paradoxically, that all convergently evolved cheater lineages have similar fusion deficiencies. These mutants are unable to initiate fusion but retain access to wild-type mycelia that fuse with them. This asymmetry reduces cheater-mutant contributions to somatic substrate-bound hyphal networks, but increases representation of their nuclei in the aerial reproductive hyphae. Cheaters only benefit when relatively rare and likely impose genetic load reminiscent of germline senescence. We show that the consequences of somatic fusion can be unequally distributed among fusion partners, with the passive non-fusing partner profiting more. We discuss how our findings may relate to the extensive variation in fusion frequency of fungi found in nature

Evaluation of sequencing and PCR-based methods for the quantification of the viral genome formula

Viruses show great diversity in their genome organization. Multipartite viruses package their genome segments into separate particles, most or all of which are required to initiate infection in the host cell. The benefits of such seemingly inefficient genome organization are not well understood. One hypothesised benefit of multipartition is that it allows for flexible changes in gene expression by altering the frequency of each genome segment in different environments, such as encountering different host species. The ratio of the frequency of segments is termed the genome formula (GF). Thus far, formal studies quantifying the GF have been performed for well-characterised virus-host systems in experimental settings using RT-qPCR. However, to understand GF variation in natural populations or novel virus-host systems, a comparison of several methods for GF estimation including high-throughput sequencing (HTS) based methods is needed. Currently, it is unclear how HTS-methods compare a golden standard, such as RT-qPCR. Here we show a comparison of multiple GF quantification methods (RT-qPCR, RT-digital PCR, Illumina RNAseq and Nanopore direct RNA sequencing) using three host plants (Nicotiana tabacum, Nicotiana benthamiana, and Chenopodium quinoa) infected with cucumber mosaic virus (CMV), a tripartite RNA virus. Our results show that all methods give roughly similar results, though there is a significant method effect on genome formula estimates. While the RT-qPCR and RT-dPCR GF estimates are congruent, the GF estimates from HTS methods deviate from those found with PCR. Our findings emphasize the need to tailor the GF quantification method to the experimental aim, and highlight that it may not be possible to compare HTS and PCR-based methods directly. The difference in results between PCR-based methods and HTS highlights that the choice of quantification technique is not trivial

Evaluation of sequencing and PCR-based methods for the quantification of the viral genome formula

Viruses show great diversity in their genome organization. Multipartite viruses package their genome segments into separate particles, most or all of which are required to initiate infection in the host cell. The benefits of such seemingly inefficient genome organization are not well understood. One hypothesised benefit of multipartition is that it allows for flexible changes in gene expression by altering the frequency of each genome segment in different environments, such as encountering different host species. The ratio of the frequency of segments is termed the genome formula (GF). Thus far, formal studies quantifying the GF have been performed for well-characterised virus-host systems in experimental settings using RT-qPCR. However, to understand GF variation in natural populations or novel virus-host systems, a comparison of several methods for GF estimation including high-throughput sequencing (HTS) based methods is needed. Currently, it is unclear how HTS-methods compare a golden standard, such as RT-qPCR. Here we show a comparison of multiple GF quantification methods (RT-qPCR, RT-digital PCR, Illumina RNAseq and Nanopore direct RNA sequencing) using three host plants (Nicotiana tabacum, Nicotiana benthamiana, and Chenopodium quinoa) infected with cucumber mosaic virus (CMV), a tripartite RNA virus. Our results show that all methods give roughly similar results, though there is a significant method effect on genome formula estimates. While the RT-qPCR and RT-dPCR GF estimates are congruent, the GF estimates from HTS methods deviate from those found with PCR. Our findings emphasize the need to tailor the GF quantification method to the experimental aim, and highlight that it may not be possible to compare HTS and PCR-based methods directly. The difference in results between PCR-based methods and HTS highlights that the choice of quantification technique is not trivial

Somatic deficiency causes reproductive parasitism in a fungus

Some multicellular organisms can fuse because mergers potentially provide mutual benefits. However, experimental evolution in the fungus Neurospora crassa has demonstrated that free fusion of mycelia favours cheater lineages, but the mechanism and evolutionary dynamics of dishonest exploitation are unknown. Here we show, paradoxically, that all convergently evolved cheater lineages have similar fusion deficiencies. These mutants are unable to initiate fusion but retain access to wild-type mycelia that fuse with them. This asymmetry reduces cheater-mutant contributions to somatic substrate-bound hyphal networks, but increases representation of their nuclei in the aerial reproductive hyphae. Cheaters only benefit when relatively rare and likely impose genetic load reminiscent of germline senescence. We show that the consequences of somatic fusion can be unequally distributed among fusion partners, with the passive non-fusing partner profiting more. We discuss how our findings may relate to the extensive variation in fusion frequency of fungi found in nature

Somatic deficiency causes reproductive parasitism in a fungus

Some multicellular organisms can fuse because mergers potentially provide mutual benefits. However, experimental evolution in the fungus Neurospora crassa has demonstrated that free fusion of mycelia favours cheater lineages, but the mechanism and evolutionary dynamics of this exploitation are unknown. Here we show, paradoxically, that all convergently evolved cheater lineages have similar fusion deficiencies. These mutants are unable to initiate fusion but retain access to wild-type mycelia that fuse with them. This asymmetry reduces cheater-mutant contributions to somatic substrate-bound hyphal networks, but increases representation of their nuclei in the aerial reproductive hyphae. Cheaters only benefit when relatively rare and likely impose genetic load reminiscent of germline senescence. We show that the consequences of somatic fusion can be unequally distributed among fusion partners, with the passive non-fusing partner profiting more. We discuss how our findings may relate to the extensive variation in fusion frequency of fungi found in nature

Membrane lipids and soluble sugars dynamics of the alkaliphilic fungus Sodiomyces tronii in response to ambient pH

Alkaliphily, the ability of an organism to thrive optimally at high ambient pH, has been well-documented in several lineages: archaea, bacteria and fungi. The molecular mechanics of such adaptation has been extensively addressed in alkaliphilic bacteria and alkalitolerant fungi. In this study, we consider an additional property that may have enabled fungi to prosper at alkaline pH: altered contents of membrane lipids and cytoprotectant molecules. In the alkaliphilic Sodiomyces tronii, we showed that at its optimal growth pH 9.2, the fungus accumulates abundant cytosolic trehalose (4–10% dry weight) and phosphatidic acids in the membrane lipids, properties not normally observed in neutrophilic species. At a very high pH 10.2, the major carbohydrate, glucose, was rapidly substituted by mannitol and arabitol. Conversely, lowering the pH to 5.4–7.0 had major implications both on the content of carbohydrates and membrane lipids. It was shown that trehalose dominated at pH 5.4. Fractions of sphingolipids and sterols of plasma membranes rapidly elevated possibly indicating the formation of membrane structures called rafts. Overall, our results reveals complex dynamics of the contents of membrane lipids and cytoplasmic sugars in alkaliphilic S. tronii, suggesting their adaptive functionality against pH stress

The alkalophilic fungus <i>Sodiomyces alkalinus</i> hosts beta- and gammapartitiviruses together with a new fusarivirus - Fig 3

<p>Phylogeny of the <i>Sodiomyces</i> sp. based on the ITS rDNA sequences (A), with the origin location of dsRNA-containing strains and phylogeny of the SaFV1 isolates based on the whole genome sequence (B).</p