International Symposium on Cereal Leaf Blights 2019 | University College Dublin, Ireland | 22-24 May 2019

Chlamydospore of Zymoseptoria tritici: from morphogenesis to the genetic control

Carolina Sardinha Francisco*

Bruce A. McDonald

Javier Palma-Guerrero

Poster Presentation
Pathogen Functional Genetics and Genomics

Atrium, UCD O'Brien centre for Science
Poster 27

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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 grant survival. We characterized the responses of Zymoseptoria tritici to a series of environmental stresses to understand the effects of changing environments on fungal morphology and adaptation. This led to the discovery that Z. tritici forms chlamydospores. Though chlamydospores were especially prominent in one of the tested strains (1A5), we observed chlamydospore production in all four strains (1A5, 1E4, 3D1, and 3D7) both in vitro and in planta. We demonstrated that chlamydospores are better able to survive extreme cold, heat, drought and are also the most resistant morphotype to fungicides. Moreover, we demonstrated that the chlamydospore formation ability is present worldwide. We also used the natural morphological variation among Z. tritici strains to determine the genetic architecture of cell morphology by quantitative trait loci (QTL) mapping. We phenotyped 230 offspring isolates from the cross between 1E4 (mainly hyphal growth) and 1A5 (only chlamydospore formation) at 27°C. QTL mapping analysis identified a 95% confidence interval containing only eight genes. Two of them encoded transcription factors (TF1 and TF2) and another two encoded phosphatases that were highly polymorphic among the parental strains. Functional characterization of both transcription factors indicated that they are putative repressor of hyphal growth. We hypothesize that the alleles from 1A5 lead to a complete repression of the morphological transition to hyphal growth in 1A5, which results in chlamydospore formation as an extreme stress response morphotype. Our results illustrate that a foliar wheat pathogen produces chlamydospores that enable the pathogen to survive under highly stressful conditions. Natural genetic variation enabled us to identify new genes involved in the morphological stress response.