The central insight of the review is that nutrient limitation operates in two interconnected modes. On one hand, starvation is a metabolic stress that passively restricts growth by depriving cells of the energy and building blocks needed for proliferation. On the other hand, and more strikingly, nutrient scarcity functions as information: it tells the fungus that continued local growth is becoming unprofitable and that dispersal, dormancy, or recombination may offer better future returns. This adaptive duality, the authors argue, has driven the evolution of precise sensing pathways that transform an environmental deficit into an anticipatory cue for fitness realignment. The result is a developmental window in which fungi can commit to reproduction, but only if they retain enough physiological competence to complete the costly program.

The clearest illustration comes from budding yeast, Saccharomyces cerevisiae, which enters meiotic sporulation only under a specific combination of conditions: the cells must be diploid with both mating types, starved of nitrogen, depleted of fermentable glucose, and supplied with a non-fermentable carbon source such as acetate. Each element of this recipe is physiologically coherent. Nitrogen limitation reduces the value of mitotic division, glucose depletion lifts repression of respiratory and meiotic programs, and acetate fuels meiosis and spore-wall construction. Under nutrient-rich conditions, the conserved cAMP-PKA and TOR signaling pathways promote growth and actively suppress meiotic genes; when conditions turn unfavorable, that repression is relieved and the master meiotic regulators IME1 and IME2 are induced. Sporulation, in other words, is a conditional developmental program, not a nonspecific starvation collapse.

Fission yeast, Schizosaccharomyces pombe, achieves a similar outcome through a different regulatory architecture. Nitrogen starvation is the principal cue that triggers sexual differentiation: compatible mating types arrest in the G1 phase of the cell cycle, mate, fuse their nuclei, enter meiosis, and produce stress-resistant spores. The pathway runs through the transcription factor Ste11, which induces mating and meiotic genes once growth-promoting cAMP-PKA and TOR signals subside. Commitment is then controlled by a molecular switch involving the Pat1 kinase and the RNA-binding protein Mei2. During vegetative growth, Pat1 phosphorylates Mei2 and marks it for destruction; upon nitrogen starvation and successful conjugation, the inhibitor Mei3 is expressed, Pat1 is inactivated, and the cell becomes irreversibly committed to meiosis. The comparison between the two yeasts supports a modular model in which conserved nutrient-sensing pathways feed into species-specific reproductive circuits.

Filamentous fungi add further layers of complexity. In Aspergillus nidulans, the best-defined genetic model, asexual development depends on the BrlA-AbaA-WetA transcriptional cascade, with BrlA initiating conidiophore construction, AbaA directing phialide differentiation, and WetA ensuring spore maturation and long-term viability. Upstream regulators such as FluG and the Flb proteins connect colony state to this central cascade, while light and the Velvet complex bias the outcome: light generally favors asexual conidiation, whereas darkness promotes sexual development through the nuclear accumulation of the VeA protein. In Neurospora crassa, the White Collar Complex and the FRQ-based circadian clock generate rhythmic conidiation, timing spore production to predictable daily cycles. In plant pathogens such as Magnaporthe oryzae and Fusarium graminearum, nutrient limitation intertwines with host-derived stresses, and the resulting spores, conidia in rice blast or airborne ascospores in Fusarium head blight, are the engines of epidemic spread.

Human fungal pathogens reveal the clinical stakes of these switches. In Candida albicans, the white-opaque epigenetic switch has long been considered a prerequisite for mating, but recent work shows that glucose depletion can bypass it entirely, rendering white cells mating-competent without the switch. Phosphate limitation, acting through the PHO pathway, can similarly induce the opaque state even in otherwise mating-incompetent cells. In Cryptococcus neoformans, whose sexual reproduction produces the basidiospores that serve as primary infectious propagules, all fourteen core autophagy genes are required for meiotic progression and spore formation, and the heme activator protein complex links iron homeostasis directly to sexual development by repressing the pheromone-responsive Cpk1 MAPK pathway. These findings underscore that nutrient sensing and reproductive commitment are deeply entangled even under host-imposed selection.

Perhaps the most striking recent discovery concerns a post-transcriptional layer of control. In the class Sordariomycetes, sexual development is accompanied by extensive adenosine-to-inosine mRNA editing, mediated not by the animal-style ADAR enzymes but by a fungal-specific Tad2-Tad3-Ame1 complex. Because inosine is read as guanosine during translation, this editing generates transcript-level changes that alter codons without touching the genome. The editing occurs almost exclusively during fruiting-body development and ascospore formation, and experimental studies in Fusarium and Neurospora show that it contributes to perithecium development, meiosis, and spore maturation through targets such as Dbf2, Mus81, and Spo11. Crucially, by restricting reproduction-beneficial protein variants to the sexual phase, editing allows fungi to preserve vegetative stress resilience, such as Mus81-dependent heat tolerance, while still meeting the distinct genetic demands of meiosis, elegantly resolving the antagonistic pleiotropy between survival and reproduction.

Why should a fungus pay the steep cost of sex when clonal spores can disperse and survive just as well? The review evaluates two evolutionary frameworks. Fitness-associated sex theory proposes that low-fitness individuals benefit from recombination because sex allows alleles to escape maladapted genetic backgrounds. Experimental work in Aspergillus nidulans supports this: sexual reproduction is associated with low-fitness conditions, and sublethal fungicide stress increases outcrossing, with recombinant offspring showing improved performance under stress. The abandon-ship framework extends the logic, treating dispersal, dormancy, and sex as alternative escape routes from a deteriorating situation: escape in space through conidia, escape in time through chlamydospores and sclerotia, and escape in genetic identity through recombination. Both models predict that the beneficiaries of stress-induced sex may be the recombinant offspring rather than the stressed parent, a distinction that demands careful measurement of parental condition, propagule quality, and descendant performance.

The practical implications are substantial. In industrial biotechnology, a rational two-phase strategy, first building biomass under favorable conditions and then applying controlled developmental cues, can maximize yields of viable, stress-tolerant spores for biocontrol agents, inoculants, and fermentation starters, with mechanistic markers such as conidiation-regulator expression guiding the timing of the shift. In agriculture and medicine, anti-sporulation interventions range from highly specific targets such as the BrlA and WetA transcription factors to broader signaling nodes and environmental management of light, humidity, and crop residues. Yet the authors caution that conserved regulators carry risks for beneficial fungi and that strong selective pressure under field conditions can drive pathogens toward altered sporulation kinetics or cryptic alternative pathways. The review closes with a call for causal, ecologically grounded models that link environmental perception, molecular regulation, reproductive output, and fitness consequences, moving the field from describing stress-associated reproduction to predicting and ultimately manipulating fungal life-history decisions.

Subject of Research: Stress-driven sporulation and sexual development in fungi

Article Title: When growth becomes risky: stress-driven sporulation and sexual development in fungi

Article References: Yang, J., Wang, Q., & Liu, H. (2026). When growth becomes risky: stress-driven sporulation and sexual development in fungi. Stress Biology, 6(1), Article 55. https://doi.org/10.1007/s44154-026-00333-1

Image Credits: AI Generated

DOI: 10.1007/s44154-026-00333-1

Keywords: fungal development, sporulation, sexual reproduction, nutrient limitation, stress signaling, cAMP-PKA, TOR signaling, HOG MAPK, Velvet complex, A-to-I RNA editing, fitness-associated sex, disease management