Pseudoflowers produced by Fusarium xyrophilum on yellow-eyed grass (Xyris spp.) in Guyana: A novel floral mimicry system?

Terpenes modulate bacterial and fungal growth and sorghum rhizobiome communities

Terpenes are among the oldest and largest class of plant-specialized bioproducts that are known to affect plant development, adaptation, and biological interactions. While their biosynthesis, evolution, and function in aboveground interactions with insects and individual microbial species are well studied, how different terpenes impact plant microbiomes belowground is much less understood. Here we designed an experiment to assess how belowground exogenous applications of monoterpenes (1,8-cineole and linalool) and a sesquiterpene (nerolidol) delivered through an artificial root system impacted its belowground bacterial and fungal microbiome. We found that the terpene applications had significant and variable impacts on bacterial and fungal communities, depending on terpene class and concentration; however, these impacts were localized to the artificial root system and the fungal rhizosphere. We complemented this experiment with pure culture bioassays on responsive bacteria and fungi isolated from the sorghum rhizobiome. Overall, higher concentrations (200 µM) of nerolidol were inhibitory to Ferrovibrium and tested Firmicutes. While fungal isolates of Penicillium and Periconia were also more inhibited by higher concentrations (200 µM) of nerolidol, Clonostachys was enhanced at this higher level and together with Humicola was inhibited by the lower concentration tested (100 µM). On the other hand, 1,8-cineole had an inhibitory effect on Orbilia at both tested concentrations but had a promotive effect at 100 µM on Penicillium and Periconia. Similarly, linalool at 100 µM had significant growth promotion in Mortierella, but an inhibitory effect for Orbilia. Together, these results highlight the variable direct effects of terpenes on single microbial isolates and demonstrate the complexity of microbe-terpene interactions in the rhizobiome. IMPORTANCE Terpenes represent one of the largest and oldest classes of plant-specialized metabolism, but their role in the belowground microbiome is poorly understood. Here, we used a "rhizobox" mesocosm experimental set-up to supply different concentrations and classes of terpenes into the soil compartment with growing sorghum for 1 month to assess how these terpenes affect sorghum bacterial and fungal rhizobiome communities. Changes in bacterial and fungal communities between treatments belowground were characterized, followed by bioassays screening on bacterial and fungal isolates from the sorghum rhizosphere against terpenes to validate direct microbial responses. We found that microbial growth stimulatory and inhibitory effects were localized, terpene specific, dose dependent, and transient in time. This work paves the way for engineering terpene metabolisms in plant microbiomes for improved sustainable agriculture and bioenergy crop production.

Mycophagy: A Global Review of Interactions between Invertebrates and Fungi

Fungi are diverse organisms that occupy important niches in natural settings and agricultural settings, acting as decomposers, mutualists, and parasites and pathogens. Interactions between fungi and other organisms, specifically invertebrates, are understudied. Their numbers are also severely underestimated. Invertebrates exist in many of the same spaces as fungi and are known to engage in fungal feeding or mycophagy. This review aims to provide a comprehensive, global view of mycophagy in invertebrates to bring attention to areas that need more research, by prospecting the existing literature. Separate searches on the Web of Science were performed using the terms "mycophagy" and "fungivore". Invertebrate species and corresponding fungal species were extracted from the articles retrieved, whether the research was field- or laboratory-based, and the location of the observation if field-based. Articles were excluded if they did not list at least a genus identification for both the fungi and invertebrates. The search yielded 209 papers covering seven fungal phyla and 19 invertebrate orders. Ascomycota and Basidiomycota are the most represented fungal phyla whereas Coleoptera and Diptera make up most of the invertebrate observations. Most field-based observations originated from North America and Europe. Research on invertebrate mycophagy is lacking in some important fungal phyla, invertebrate orders, and geographic regions.

Distribution, Function, and Evolution of a Gene Essential for Trichothecene Toxin Biosynthesis in Trichoderma

Trichothecenes are terpenoid toxins produced by species in 10 fungal genera, including species of Trichoderma. The trichothecene biosynthetic gene (tri) cluster typically includes the tri5 gene, which encodes a terpene synthase that catalyzes formation of trichodiene, the parent compound of all trichothecenes. The two Trichoderma species, Trichoderma arundinaceum and T. brevicompactum, that have been examined are unique in that tri5 is located outside the tri cluster in a genomic region that does not include other known tri genes. In the current study, analysis of 35 species representing a wide range of the phylogenetic diversity of Trichoderma revealed that 22 species had tri5, but only 13 species had both tri5 and the tri cluster. tri5 was not located in the cluster in any species. Using complementation analysis of a T. arundinaceum tri5 deletion mutant, we demonstrated that some tri5 homologs from species that lack a tri cluster are functional, but others are not. Phylogenetic analyses suggest that Trichoderma tri5 was under positive selection following its divergence from homologs in other fungi but before Trichoderma species began diverging from one another. We propose two models to explain these diverse observations. One model proposes that the location of tri5 outside the tri cluster resulted from loss of tri5 from the cluster in an ancestral species followed by reacquisition via horizontal transfer. The other model proposes that in species that have a functional tri5 but lack the tri cluster, trichodiene production provides a competitive advantage.

Fungal social influencers: secondary metabolites as a platform for shaping the plant-associated community

Fungal secondary metabolites (FSMs) are capable of manipulating plant community dynamics by inhibiting or facilitating the establishment of co-habitating organisms. Although production of FSMs is not crucial for survival of the producer, their absence can indirectly impair growth and/or niche competition of these fungi on the plant. The presence of FSMs with no obvious consequence on the fitness of the producer leaves questions regarding ecological impact. This review investigates how fungi employ FSMs as a platform to mediate fungal-fungal, fungal-bacterial and fungal-animal interactions associated with the plant community. We discuss how the biological function of FSMs may indirectly benefit the producer by altering the dynamics of surrounding organisms. We introduce several instances where FSMs influence antagonistic- or alliance-driven interactions. Part of our aim is to decipher the meaning of the FSM 'language' as it is widely noted to impact the surrounding community. Here, we highlight the contribution of FSMs to plant-associated interaction networks that affect the host either broadly or in ways that may have previously been unclear.

Phylogenomic Analysis of a 55.1-kb 19-Gene Dataset Resolves a Monophyletic Fusarium that Includes the Fusarium solani Species Complex

Scientific communication is facilitated by a data-driven, scientifically sound taxonomy that considers the end-user's needs and established successful practice. In 2013, the Fusarium community voiced near unanimous support for a concept of Fusarium that represented a clade comprising all agriculturally and clinically important Fusarium species, including the F. solani species complex (FSSC). Subsequently, this concept was challenged in 2015 by one research group who proposed dividing the genus Fusarium into seven genera, including the FSSC described as members of the genus Neocosmospora, with subsequent justification in 2018 based on claims that the 2013 concept of Fusarium is polyphyletic. Here, we test this claim and provide a phylogeny based on exonic nucleotide sequences of 19 orthologous protein-coding genes that strongly support the monophyly of Fusarium including the FSSC. We reassert the practical and scientific argument in support of a genus Fusarium that includes the FSSC and several other basal lineages, consistent with the longstanding use of this name among plant pathologists, medical mycologists, quarantine officials, regulatory agencies, students, and researchers with a stake in its taxonomy. In recognition of this monophyly, 40 species described as genus Neocosmospora were recombined in genus Fusarium, and nine others were renamed Fusarium. Here the global Fusarium community voices strong support for the inclusion of the FSSC in Fusarium, as it remains the best scientific, nomenclatural, and practical taxonomic option available.

OCBIL theory: a new science for old ecosystems

This paper is an introduction to the special issue of the Biological Journal of the Linnean Society entitled OCBIL theory: a new science for old ecosystems. Firstly, we elaborate on the origins and development of OCBIL theory, which argues that landscape age, climatic buffering and soil fertility are key environmental dimensions shaping ecological and evolutionary processes across different scales. We then consider the 21 contributions made in this special issue in terms of cutting edge advances in the Southern Hemisphere that test, explore and apply aspects of OCBIL theory at the end of its first decade of formal publication. More attempts at refutation are urged, as untested aspects remain controversial. Lastly, a concluding discussion is offered on promising new lines of enquiry to develop the theory further and ensure its global application to pressing conservation issues facing biological and cultural diversity. Although OCBILs are absent or rare in much of the postglacial and periglacial Northern Hemisphere, we demonstrate, in south-west Europe and North America, starting with California, that they are likely to be found, thus extending the implications and applications of OCBIL theory in new directions. We also propose that, in many ways, Noongar Aboriginal cosmology from south-west Australia has developed sophisticated insights about ancient uplands that are precursors to key ideas in OCBIL theory.

Ecology: Fungal Mimics Dupe Animals by Transforming Plants

Many fungi transform host tissues to benefit their own reproduction. A recent study investigates a fungus that converts its plant host's reproductive tissues into ornate flower mimics. These 'pseudoflowers' present complex cues that may enlist insects to facilitate fungal dispersal.