Abstract
During their life cycles, pathogens have to adapt to many biotic and abiotic environmental stresses 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, even though different morphotypes may play important biological roles. Here, we first show that blastospores (the “yeast-like” form of the pathogen typically known only under laboratory conditions) can form from germinated pycnidiospores (asexual spores) on the surface of wheat leaves, suggesting that this morphotype can play an important role in the natural history of Z. tritici. Next, we characterized the morphological responses of this fungus to a series of environmental stresses to understand the effects of changing environments on fungal morphology and adaptation. All tested stresses induced morphological changes, but different responses were found among four strains. We discovered that Z. tritici forms chlamydospores and demonstrated that these structures are better able to survive extreme cold, heat and drought than other cell types. Finally, a transcriptomic analysis showed that morphogenesis and the expression of virulence factors are co-regulated in this pathogen. Our findings illustrate how changing environmental conditions can affect cellular morphology and lead to the formation of new morphotypes, with each morphotype having a potential impact on both pathogen survival and disease epidemiology.
Highlights
Fungi occupy a wide range of niches that can impose different environmental constraints on their growth, reproduction and survival
This suggests that pycnidiospores of Z. tritici can germinate to produce additional blastospores www.nature.com/scientificreports even before penetration of the wheat leaf, providing an alternative mechanism for splash dispersal of infective propagules and potentially providing a substantial increase in the total inoculum load associated with an infection cycle
Though much research has been oriented around morphological changes and their associated transcriptional pathways in response to different stressors in fungal pathogens of humans[10,18,49], knowledge in this area is limited for plant pathogens
Summary
Fungi occupy a wide range of niches that can impose different environmental constraints on their growth, reproduction and survival. The majority of fungal morphotype transitions occur between hyphal and yeast growth forms. Fungi with this ability are called dimorphic. Some genes affecting morphogenesis in Z. tritici were identified and functionally characterized Most of these belonged to the mitogen-activated protein kinase (MAPK) or cAMP-dependent signaling pathways involved in extracellular signal transduction, regulating many cellular processes, development and virulence[30,31,32,33,34,35,36,37,38,39,40]. In this study we aimed to determine whether morphological changes allow Z. tritici to tolerate different environmental stresses and whether the different morphotypes play important biological roles. Transcriptional analyses showed co-regulation of mycelial growth and virulence factors Based on these findings, we propose that morphological transitions in Z. tritici are a stress response that allows the fungus to optimize fitness in a changing environment
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