Epigenetic control of virulence in the fungal plant pathogen, Zymoseptoria tritici

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The predicted increase in global demand for wheat means that it is essential that the supply of this food source is protected. Fungal pathogens that infect wheat are major threats to agriculture and food security. Here Septoria tritici blotch (STB) disease resulting from Zymoseptoria tritici infection represents the most serious wheat disease in Europe. Indeed in the UK alone, STB results in an annual loss of approximately £50 million. Although several fungicides are used to control Z. tritici infections many populations have evolved fungicide resistance so that new strategies to control this pathogen are required. Recently, the development of a range of molecular tools for Z. tritici has provided an opportunity to decipher the pathways that regulate its pathogenicity and inform new strategies for its control. . Like many other plant and human fungal pathogens, an important aspect of Z. tritici virulence is likely its ability to switch morphology. Indeed, Z. tritici infection is accompanied by a switch to hyphal growth and the induction in the expression of effector-encoding genes. Recently it has been shown that prior to wheat infection, effector-encoding genes are located in chromatin that is enriched with heterochromatic marks, histone H3 lysine 9 and 27 methylation (H3K9me/H3K27me). This suggests that reprogramming of these repressive heterochromatic marks is required for the proper induction of gene expression during the infection process. Therefore, the aim of this project is to determine the role of heterochromatin in the control of morphological switching and virulence of Z. tritici. Chromatin immunoprecipitation analysis will be employed to determine changes in histone modifications during morphological switching. Furthermore, analysis of the Z. tritici genome sequence database has revealed the genes encoding the H3K9- and the H3K27-histone methylase transferases. Therefore a key objective will be the construction of strains carrying a deletion mutation in one or both histone methylase transferase genes. Using these knockout strains it will be possible to determine the impact of disrupting heterochromatin upon organism fitness, morphogenic switching, effector gene expression and ultimately the ability to cause infection in wheat.