183V Poster Online - Virtual Posters
Tuesday June 07, 11:00 AM - 3:00 PM

Authors:
Dilay Hazal Ayhan ¹; Kaito Hioki ¹; Domingo Martínez-Soto ¹; Serena Abbondante ²; Michaela Ellen Marshall ²; Cristina López Díaz ³; Neta Shlezinger ⁴; Eric Pearlman ²; Antonio Di Pietro ³; Li-Jun Ma ¹

Affiliations:
1) University of Massachusetts Amherst, MA; 2) University of California Irvine, CA; 3) Universidad de Córdoba, Spain; 4) The Hebrew University of Jerusalem, Israel

Keywords:
Experimental evolution

F. oxysporum is a cross-kingdom pathogenic fungus that can cause vascular wilt disease in many plant species and can infect animals and cause local or disseminated fusariosis in humans. To be able to infect humans, fungal pathogens must overcome some biotic and abiotic stresses, such as adapting to elevated body temperature.
Focusing on temperature adaptation, we conducted comparative evolution experiments using a plant pathogenic isolate (F. oxysporum f. sp. lycopersici Fol4287) and a keratitis strain isolated from the cornea of a patient (MRL8996). Both strains were passaged 10 times through media plates with minimal or rich nutrients, at 28°C or 34°C, with 5 independent replicates.
Belonging to the same species complex, Fol4287 and MRL8996 share a core genome with an average 98% nucleotide identity. However, each genome has its own distinct accessory chromosomes (ACs) with different gene ontology enrichments and transposable element (TE) contents. At the start of the short-term experimental evolution study, the human pathogenic strain MRL8996 exhibited higher fitness at elevated temperatures, while the plant pathogen Fol4287 had more tolerance to the osmatic and cell wall stress conditions.
After 10 passages, we observed the most significant phenotypic difference among Fol4287 populations evolved under elevated temperature, showing significant improvement in heat tolerance when compared to the ancestor. As a trade-off, these populations showed a reduced growth rate in some of the other stress conditions, such as oxidative and osmotic stresses.
Sequencing of the final populations revealed signatures of weak selection in the evolved MRL8996 populations with low-frequency TE insertion events by a hyper-active Foxy element. While TEs were also highly active in Fol4287, different patterns and TE families were involved.
Strikingly, an uncharacterized accessory chromosome gene was mutated by a DNA transposon, Hormin, in 8 out of 10 34°C-passaged Fol4287 populations that also showed increased heat tolerance. The mutation site is located in between a gene block that is upregulated at elevated temperature and a gene block that is up-regulated in plant infection.
Overall, our study demonstrated although similar mechanisms were employed in different F. oxysporum strains, the adaptation to elevated temperatures was distinct and ACs played an important role.