ABSTRACT
During their life cycles, pathogens have to adapt to many biotic and abiotic environmental constraints to maximize their overall fitness. Morphological transitions are one of the least understood of the many strategies employed by fungal plant pathogens to adapt to constantly changing environments. We characterized the responses of the wheat pathogen Zymoseptoria tritici to a series of environmental stimuli using microscopy, transcriptomic analyses, and survival assays to explore the effects of changing environments on morphology and adaptation. We found that all tested stimuli induced morphological changes, with distinct responses observed among four different strains. The transcription analyses indicated a co-regulation of morphogenesis and virulence factors in Z. tritici. We discovered that Z. tritici forms chlamydospores and we demonstrate that these survival structures are better able to withstand extreme cold, heat and drought than other cell types. We also demonstrate that blastospores (the “yeast-like” form typically found only in vitro) can form from germinated pycnidiospores on the wheat leaf surface, suggesting that this morphotype can play an important role in the natural history of Z. tritici. Our experiments illustrate how changing environmental conditions can affect cellular morphology and lead to the formation of new morphotypes that can have a significant impact on both pathogen survival and disease epidemiology.