Olfactory Preferences of the Parasitic Nematode Howardula aoronymphium and its Insect Host Drosophila falleni

Lessons on fruiting body morphogenesis from genomes and transcriptomes of Agaricomycetes

Fruiting bodies (sporocarps, sporophores or basidiomata) of mushroom-forming fungi (Agaricomycetes) are among the most complex structures produced by fungi. Unlike vegetative hyphae, fruiting bodies grow determinately and follow a genetically encoded developmental program that orchestrates their growth, tissue differentiation and sexual sporulation. In spite of more than a century of research, our understanding of the molecular details of fruiting body morphogenesis is still limited and a general synthesis on the genetics of this complex process is lacking. In this paper, we aim at a comprehensive identification of conserved genes related to fruiting body morphogenesis and distil novel functional hypotheses for functionally poorly characterised ones. As a result of this analysis, we report 921 conserved developmentally expressed gene families, only a few dozens of which have previously been reported to be involved in fruiting body development. Based on literature data, conserved expression patterns and functional annotations, we provide hypotheses on the potential role of these gene families in fruiting body development, yielding the most complete description of molecular processes in fruiting body morphogenesis to date. We discuss genes related to the initiation of fruiting, differentiation, growth, cell surface and cell wall, defence, transcriptional regulation as well as signal transduction. Based on these data we derive a general model of fruiting body development, which includes an early, proliferative phase that is mostly concerned with laying out the mushroom body plan (via cell division and differentiation), and a second phase of growth via cell expansion as well as meiotic events and sporulation. Altogether, our discussions cover 1 480 genes of Coprinopsis cinerea, and their orthologs in Agaricus bisporus, Cyclocybe aegerita, Armillaria ostoyae, Auriculariopsis ampla, Laccaria bicolor, Lentinula edodes, Lentinus tigrinus, Mycena kentingensis, Phanerochaete chrysosporium, Pleurotus ostreatus, and Schizophyllum commune, providing functional hypotheses for ~10 % of genes in the genomes of these species. Although experimental evidence for the role of these genes will need to be established in the future, our data provide a roadmap for guiding functional analyses of fruiting related genes in the Agaricomycetes. We anticipate that the gene compendium presented here, combined with developments in functional genomics approaches will contribute to uncovering the genetic bases of one of the most spectacular multicellular developmental processes in fungi. Citation: Nagy LG, Vonk PJ, Künzler M, Földi C, Virágh M, Ohm RA, Hennicke F, Bálint B, Csernetics Á, Hegedüs B, Hou Z, Liu XB, Nan S, M. Pareek M, Sahu N, Szathmári B, Varga T, Wu W, Yang X, Merényi Z (2023). Lessons on fruiting body morphogenesis from genomes and transcriptomes of Agaricomycetes. Studies in Mycology 104: 1-85. doi: 10.3114/sim.2022.104.01.

Coprinopsis cinerea dioxygenase is an oxygenase forming 10(S)-hydroperoxide of linoleic acid, essential for mushroom alcohol, 1-octen-3-ol synthesis

1-Octen-3-ol is a volatile oxylipin found ubiquitously in Basidiomycota and Ascomycota. The biosynthetic pathway forming 1-octen-3-ol from linoleic acid via the linoleic acid 10(S)-hydroperoxide was characterized 40 years ago in mushrooms, yet the enzymes involved are not identified. The dioxygenase 1 and 2 genes (Ccdox1 and Ccdox2) in the mushroom Coprinopsis cinerea contain an N-terminal cyclooxygenase-like heme peroxidase domain and a C-terminal cytochrome P450-related domain. Herein, we show that recombinant CcDOX1 is responsible for dioxygenation of linoleic acid to form the 10(S)-hydroperoxide, the first step in 1-octen-3-ol synthesis, whereas CcDOX2 conceivably forms linoleate 8-hydroperoxide. We demonstrate that knockout of the Ccdox1 gene suppressed 1-octen-3-ol synthesis, although added linoleic acid 10(S)-hydroperoxide was still efficiently converted. The P450-related domain of CcDOX1 lacks the characteristic Cys heme ligand and the evidence indicates that a second uncharacterized enzyme converts the 10(S)-hydroperoxide to 1-octen-3-ol. Additionally, we determined the gene knockout strain (ΔCcdox1) was less attractive to fruit fly larvae, while the feeding behavior of fungus gnats on ΔCcdox1 mycelia showed little difference from that on the mycelia of the wild-type strain. The proliferation of fungivorous nematodes on ΔCcdox1 mycelia was similar to or slightly worse than that on wild-type mycelia. Thus, 1-octen-3-ol seems to be an attractive compound involved in emitter-receiver ecological communication in mushrooms.

Natural variation in host-finding behaviour of gastropod parasitic nematodes (Phasmarhabditis spp.) exposed to host-associated cues

The gastropod parasitic nematode Phasmarhabditis hermaphrodita has been formulated into a successful biological control agent (Nemaslug®, strain DMG0001) used to kill slugs on farms and gardens. When applied to soil, P. hermaphrodita uses slug mucus and faeces to find potential hosts. However, there is little information on what cues other species of Phasmarhabditis (P. neopapillosa and P. californica) use to find hosts and whether there is natural variation in their ability to chemotax to host cues. Therefore, using chemotaxis assays, we exposed nine wild isolates of P. hermaphrodita, five isolates of P. neopapillosa and three isolates of P. californica to mucus from the pestiferous slug host Deroceras invadens, as well as 1% and 5% hyaluronic acid - a component of slug mucus that is highly attractive to these nematodes. We found P. hermaphrodita (DMG0010) and P. californica (DMG0018) responded significantly more to D. invadens mucus and 1% hyaluronic acid than other strains. Also, P. hermaphrodita (DMG0007), P. neopapillosa (DMG0015) and P. californica (DMG0017) were superior at locating 5% hyaluronic acid compared to other isolates of the same genera. Ultimately, there is natural variation in chemoattraction in Phasmarhabditis nematodes, with some strains responding significantly better to host cues than others.

Volatilomes of Cyclocybe aegerita during different stages of monokaryotic and dikaryotic fruiting

Volatile organic compounds (VOC) are characteristic for different fungal species. However, little is known about VOC changes during development and their biological role. Therefore, we established a laboratory cultivation system in modified crystallizing dishes for analyzing VOC during fruiting body development of the dikaryotic strainCyclocybe aegeritaAAE-3 as well as four monokaryotic offspring siblings exhibiting different fruiting phenotypes. From these, VOC were extracted directly from the headspace (HS) and analyzed by means of gas chromatography-mass spectrometry (GC-MS). For all tested strains, alcohols and ketones, including oct-1-en-3-ol, 2-methylbutan-1-ol and cyclopentanone, were the dominant substances in the HS of early developmental stages. In the dikaryon, the composition of the VOC altered with ongoing fruiting body development and, even more drastically, during sporulation. At the latter stage, sesquiterpenes, especially Δ6-protoilludene, α-cubebene and δ-cadinene, were the dominant substances. After sporulation, the amount of sesquiterpenes decreased, while additional VOC, mainly octan-3-one, appeared. In the HS of the monokaryons, less VOC were present of which all were detectable in the HS of the dikaryonC. aegeritaAAE-3. The results of the present study show that the volatilome ofC. aegeritachanges considerably depending on the developmental stage of the fruiting body.

The saprophytic fungus Fusarium solani increases the insecticidal efficacy of the entomopathogenic nematode Steinernema diaprepesi

In two field surveys, high proportions of Galleria mellonella L. (Lepidoptera: Pyralidae) sentinel larval cadavers were infected by Fusarium solani without evidence of concomitant entomopathogenic nematode (EPN) or entomopathogenic fungus (EPF) reproduction. Because F. solani is not considered entomopathogenic, the survey suggested the possibility that F. solani competes with EPNs. We tested the hypotheses that F. solani attracts the EPN, Steinernema diaprepesi, to facilitate infection of Diaprepes root weevils (Diaprepes abbreviatus L.) and thereafter competes with the nematode in the insect cadaver. In two-choice olfactometer assays where one side was treated with F. solani mycelia and conidia, juvenile S. diaprepesi were attracted to the fungus, in either raw soil, or in autoclaved soil in the presence or absence of insects. However, this attraction was attenuated as the habitat became more complex, by using raw soil in combination with insect larvae. Fusarium oxysporum did not recruit the nematode. When soil microcosms were tested with F. solani conidia and S. diaprepesi, the concomitant infection increased the mortality of the insect (P = 0.02) to 83%, compared to 58% and 0% mortality when nematodes or fungi were individually applied, respectively. Concomitant inoculation also increased the number of cadavers that supported nematode reproduction and increased the population density of fungus in soil. The number of IJs entering the host insect was not affected by F. solani. These results support the possibility that F. solani can facilitate the insecticidal efficiency of S. diaprepesi in order to exploit the resources in the cadaver.