Temperature and genetic background drive mobilization of diverse transposable elements in a critical human fungal pathogen.

Transposable elements (TEs) are key agents of genome evolution across all domains of life. These mobile genetic elements can cause mutations through transposition or by promoting structural rearrangements. Stress conditions can amplify TE activity, either by impairing TE suppression mechanisms or through stress-induced interactions between transcription factors and TE sequences, offering a route for rapid genetic change. As such, TEs represent an important source of adaptability within populations. To investigate the interplay between environmental stress and eukaryotic TE dynamics relevant to infectious disease, we examined how heat stress and nutrient limitation affect TE mobility in the human fungal pathogen Cryptococcus neoformans, using a collection of clinical and environmental isolates. Seven distinct mobile element families, encompassing diverse retrotransposons and DNA transposons, were captured mobilizing to confer antifungal resistance, including a novel element, CNEST, which belongs to the CACTA, Mirage, Chapaev (CMC) supergroup. Heat stress at human body temperature (37°C) significantly increased the mobilization of a subset of these TEs, leading to higher rates of acquired antifungal resistance. Whole-genome assemblies revealed that, compared to retrotransposons, DNA transposons were hypomethylated and approximately uniformly distributed throughout the genome, features that may contribute to their frequent mobilization. We further assessed TE-driven genomic changes within hosts using serial isolates from patients with recurrent cryptococcal infections and from isolates passaged through mice. While we observed evidence of TE copy number changes near chromosome ends, we found no indication of TE-mediated alterations near gene-coding regions across any of the serial isolates. Finally, TE mobility was isolate- and strain-dependent, with significant variation even among clonally related isolates collected from the same patient, emphasizing the role of genetic background in shaping TE activity. Together, these findings reveal a complex, dynamic relationship between environmental stress, genetic background, and TE mobility, with important implications for adaptation and acquired antifungal resistance in C. neoformans.