Research Information System
33rd Fungal Genetics Conference, California, United States Of America, 17 - 21 March 2026, (Unpublished)
Fusarium oxysporum is a cross-kingdom pathogen comprising diverse strains that cause disseminated fusariosis and keratitis in humans and vascular wilt diseases in plants. Our previous study documented that the wildtype strain MRL8996 exhibits higher thermotolerance than wildtype plant-pathogenic isolates such as Fol4287. To investigate mechanisms of adaptation to animal hosts, we conducted short-term evolution experiments with MRL8996, a keratitis isolate associated with contact lens use.
The ancestral strain was propagated into identical starting populations, evolved for ten passages under in vitro conditions (rich or minimal media at 28°C or 34°C adjusted to pH 5 or pH 7.4) and in vivo during mouse corneal infection with five biological replicates. The most distinct phenotypic variation is the loss of thermotolerance in 28°C-evolved populations.
Whole-genome sequencing revealed a striking genomic variation of the partial (28°C-evolved) or complete (34°C- and in vivo-evolved) loss of chromosome 12. Interestingly, upregulation of genes encoded in this fast-core chromosome was only detected at 28°C and pH 5, and these upregulated genes are involved in detoxification, oxidative stress defense, CAZyme-mediated plant host invasion, and heavy-metal resistance. Lacking active transcription in elevated temperature or pH suggests potential trade-offs between soil- and host-associated lifestyles.
Transposon insertion variants (TIVs) accounted for the majority of all detected mutations. SINE transposon Foxy5, the strain-specific and the highest expressed transposon in the ancestor, was the most active element, having twice the insertion frequency in accessory chromosomes than in core chromosomes. TIV numbers were more than 4-fold higher at 34°C than at 28°C. Recurrent mutations in veA and velB, components of the Velvet complex that regulate fungal development and secondary metabolism, were observed. Most TIVs occurred in promoter regions, consistent with altered gene regulation. Despite abundant variation, few mutations became fixed, indicating weak selection associated with modest phenotypic adaptation.
These findings demonstrate rapid genome remodeling in F. oxysporum MRL8996 during short-term evolution, driven by transposon activity. The concurrent loss of chromosome 12, rarely lost in other strains, highlights the evolutionary trade-offs accompanying this fungus’s transition between environmental and host-associated niches.