Global food security is continually challenged by yield losses resulting from diseases caused by plant pathogens. The most economically important disease of wheat in the UK and W. Europe is Septoria tritici blotch (STB) caused by the ascomycete fungus Zymoseptoria tritici. Alike many other plant pathogenic fungi, Z.tritici relies upon the release of secreted protein effectors to establish disease. One particular class of effector proteins, the Lysin-domain containing (LysM) secreted proteins, are released at high levels during plant infections, and function as important virulence determinants through their roles in preventing the activation of chitin-triggered immunity by plants (FEMS Microbiol. Reviews 2015 v39 p171). However, it remains currently unknown as to how these fungi know when to switch on production of these important effectors? Are there specific triggers which drive effector production? Similarly, what signalling pathways lie upstream of the promoters driving expression of these genes? Could these elements be manipulated to prevent the expression of LysM effectors with the potential to protect many crops from fungal diseases? We have previously shown that the secreted LysM effector protein "Zt3LysM" plays a major role in the virulence of Z. tritici on wheat, through preventing the early activation of plant immunity (Plant Physiol. 2011 v156 p756; Mol. Plant-Microbe Interact. 2014 v27 p236) In wild type fungal cells, the effector is strongly expressed during leaf infection with low expression observed during growth in axenic culture, away from the plant. However, we recently identified a Z. tritici mutant strain affected in a gene which likely contributes to fungal cell wall structure (a type 2 glycosyltransferase- ZtGT2), which constitutively overexpresses Zt3LysM, even in axenic culture (PLoS Pathogens 2017 v13 e1006672). This suggests that alterations to the fungal cell wall, possibly occurring through interactions with leaf surfaces, influences Zt3LysM expression levels. This project aims to define the "triggers" of LysM effector expression, and to identify fungal proteins which detect these "triggers", as well as those that transmit the trigger signal to the promoter of the effector gene to enhance its expression. The project will generate various transgenic reporter strains of Z. tritici engineered to possess the Zt3LysM gene promoter sequence fused in front of the fluorescent reporters GFP and GUS, and the subsequent use of these strains in screens to identify (1) specific triggers (chemical and or physical) of LysM effector expression and (2) mutants which fail to express the LysM effector. Candidate genes associated with the loss of effector expression will be identified through whole genome resequencing of the non-expressing strains. In addition, the promoter sequence will be used directly in screens aimed to identify the regulatory binding proteins (transcription factor(s)). Candidate genes implicated in sensing the "trigger(s)" of LysM effector expression, or mediating signalling to the effector promoter, will be further characterised by generating fungal knock-out (KO) strains of the genes in question and testing them for effector expression and virulence on wheat. Finally, the validated targets will be analysed for presence / absence in the genomes of other pathogenic fungi and avenues for potentially blocking effector expression will be explored.