Mycoviruses—viruses that infect fungi—are emerging as important regulators of fungal chemistry, according to research by Favaretto, Varotto, Kondo and colleagues published in npj Viruses. Rather than treating fungal viruses solely as passive passengers, the study examines how they can reshape the metabolic networks that determine whether fungi produce harmful mycotoxins. These naturally occurring infections may influence food safety, plant disease and the development of new biological strategies for controlling toxin-producing fungi.
Mycotoxins are chemically diverse secondary metabolites made by fungi under particular environmental and biological conditions. They include compounds such as aflatoxins, trichothecenes, fumonisins and ochratoxins, several of which can damage the liver, kidneys or immune system and create serious risks when they contaminate crops and animal feed. Their production is not essential for the fungus to grow under all circumstances, but it can provide advantages during competition, stress or infection. The underlying pathways are therefore highly responsive to signals from the fungus’s surroundings and from organisms living inside it.
Mycoviruses can alter this balance by introducing their own genetic material into fungal cells. Many belong to groups with double-stranded RNA or positive-sense single-stranded RNA genomes, although fungal viruses display considerable diversity. They generally lack the machinery required to move independently between hosts and are transmitted through fungal cell division, spores or direct contact between compatible fungal strains. Once established, a mycovirus may change the host’s gene expression, energy use, stress responses and interactions with plants or other microorganisms.
The metabolic consequences of infection can be subtle or dramatic. A virus may redirect cellular resources toward replication, interfere with protein production or activate antiviral defenses such as RNA silencing. RNA silencing uses small RNA molecules to identify and suppress matching genetic sequences, helping fungi control viral genomes. At the same time, viral infection can affect regulatory proteins, messenger RNA stability and the activity of enzymes involved in secondary metabolism. These changes may increase, decrease or completely alter the production of a mycotoxin, depending on the virus, fungal species and environmental context.
The research places particular emphasis on the connection between viral infection and metabolic regulation. Mycotoxin pathways are often organized in biosynthetic gene clusters, groups of neighboring genes that encode enzymes, transporters and regulatory factors needed to assemble and export a compound. The activity of these clusters can be controlled by global regulators responding to nutrients, oxidative stress, acidity and other conditions. Mycoviruses may influence these control systems indirectly by changing cellular redox balance, mitochondrial function or signaling pathways, or directly by affecting the expression of genes within toxin-producing clusters.
Oxidative stress is one possible link between infection and toxin formation. During viral replication or the activation of fungal defenses, cells may accumulate reactive oxygen species, chemically reactive molecules that can damage proteins and DNA but also act as signals. Fungi have antioxidant systems that keep these molecules under control, and shifts in that balance can trigger secondary metabolism. Because many mycotoxin pathways respond to oxidative conditions, a mycovirus that changes the host’s stress physiology could consequently modify toxin output without directly targeting a toxin gene.
The effects of mycoviruses are not necessarily consistent across all fungal strains. The same virus can produce different outcomes in different hosts because fungal genomes, epigenetic states, immune-like defenses and metabolic capabilities vary widely. Environmental conditions further complicate the picture. Temperature, water availability, nutrient limitation and interactions with plants or competing microbes can all influence both viral replication and mycotoxin biosynthesis. This context dependence is one reason why predicting the consequences of fungal viral infection requires integrated analysis rather than a single measurement of viral presence.
Metabolomics and transcriptomics are central to this emerging field. Metabolomics measures broad changes in small molecules, allowing researchers to identify shifts in toxins, precursors and central metabolites. Transcriptomics reveals which fungal genes become more or less active during infection, while proteomics can show whether those genetic changes result in altered enzyme abundance. Combining these approaches with viral genome sequencing and fungal genetics can help distinguish direct effects of a mycovirus from secondary changes caused by stress or altered growth. Such multi-layered analyses offer a more complete view of how viral infection is translated into chemical behavior.
The findings discussed in the study may have practical implications for agriculture and biotechnology, but they also highlight the need for caution. Mycoviruses are being investigated as potential biological control agents against plant-pathogenic fungi, especially when infection reduces fungal growth, virulence or toxin production. However, a virus that weakens one trait could theoretically enhance another, including the synthesis of an unwanted metabolite. Any application would therefore require careful screening under realistic field and storage conditions, with monitoring that measures both disease development and the complete mycotoxin profile.
By linking fungal virology with metabolic biology, the work presents mycoviruses as active participants in the chemical ecology of fungi. Understanding these relationships could improve forecasts of mycotoxin contamination and reveal new ways to manipulate fungal metabolism without relying exclusively on chemical fungicides. It may also uncover viral genes or host pathways with value for industrial biotechnology, where controlled fungal metabolism is used to produce enzymes, pharmaceuticals and other compounds. The broader message is that fungal viruses are not merely genetic stowaways: they can help determine how fungi respond to stress, interact with their hosts and shape the molecules that enter the food chain.
Subject of Research: The role of mycoviruses in regulating fungal mycotoxin production and metabolism
Article Title: The role of mycoviruses in regulating mycotoxins production: metabolic insights
Article References: Favaretto, F., Varotto, S., Kondo, H. et al. “The role of mycoviruses in regulating mycotoxins production: metabolic insights.” npj Viruses (2026). https://doi.org/10.1038/s44298-026-00221-5
Image Credits: AI Generated
DOI: 10.1038/s44298-026-00221-5
Keywords: mycoviruses, fungal viruses, mycotoxins, fungal metabolism, RNA silencing, secondary metabolism, oxidative stress, biosynthetic gene clusters, food safety, biological control
