Molecular tools for functional genomic analyses of the stealth pathogenesis of wheat by Zymoseptoria tritici

Abstract

Zymoseptoria tritici is an ascomycete fungus that causes Septoria tritici leaf blotch disease, which is one of the most devastating diseases of wheat. The lack of molecular tools has withheld functional genomics and consequently has left extensive gaps in the knowledge of the biology of infection by Z. tritici. The current research was conducted to develop molecular tools in order to facilitate forward and reserves genetic screens in Z. tritici. These tools include an optimised genetic manipulation protocol, the Z. tritici strains that provide high frequency targeted genome manipulations, a strategy for gene overexpression and protein tagging, and regulatable promoters for controlled gene expression in Z. tritici. The regulatable promoters served to reveal that the Z. tritici β-(1,3)- glucan synthase (BGS1) gene encoded an essential protein, which regulated cell wall stress tolerance and was therefore, a potential drug target. In addition, these molecular tools revealed a virulence-associated role of the glyoxylate cycle in Z. tritici as inactivation of this pathway impeded pre-penetration morphogenesis, which was restored by exogenous glucose application. This result implied that Z. tritici engaged the glyoxylate cycle to produce energy though gluconeogenesis by channelling the by-products of lipolysis. This significance of the glyoxylate cycle during initiation of the bi-phasic infection cycle suggests that Z. tritici is not a hemibiotroph, but a necrotrophic pathogen with an extended asymptomatic phase of infection. Overall, the molecular tools developed in this study will facilitate large-scale functional genomic analyses to interrogate the biology of infection by Z. tritici. The resulting data will inform the development of durable control strategies to combat Z. tritici outbreaks.