Aspergillus fumigatus is a thermotolerant saprobe found in soils and plant debris worldwide and an important pathogen of humans causing two million deaths annually. A. fumigatus makes abundant asexual spores (conidia) which are widely distributed by wind and can be inhaled from the environment. In susceptible individuals inhaled conidia break dormancy, germinate and grow in the lung leading to serious disease. Recent work has shown that conidia made at 37{degrees}C and 50{degrees}C have different morphologies and germination kinetics. While the asexual cycle is well-characterized at 37{degrees}C, much less is known about the asexual cycle at 50{degrees}C. Here, we combine flow cytometry and transcriptomics to track morphology and gene expression in the hyphae, conidiophores and conidia of A. fumigatus during asexual development at 37{degrees}C or 50{degrees}C. We show that the temperature during a narrow time window in late-stage conidiophore development dictates resulting conidial morphology, transcriptional program, and germination kinetics. As expected, conidiation at 37{degrees}C resulted in upregulation of brlA, the master regulator of asexual development, and its downstream targets in conidiophores and conidia. Surprisingly, conidiation at 50{degrees}C resulted in upregulation of MAT1-1, the master regulator of sexual development and its downstream targets in conidiophores and conidia. Our findings suggest that temperature during late conidiophore development transcriptionally primes conidia for asexual, parasexual or sexual development enhancing chances of survival for progeny. Our findings are especially relevant for agricultural compost where a wide gradient of temperatures exists, abundant A. fumigatus has been isolated, and resistance to antifungals is thought to evolve.
Stanislaw, J. M., Momany, M.
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