Abstract: Agricultural crop production is continually challenged by plant-pathogenic fungi, jeopardizing global food security. Central to plant-fungal interactions are small proteins called effectors, which can be secreted by pathogens into plant cells to promote disease. Despite their critical role during infection, the mechanisms by which most fungal effectors function remain unknown. In my project, I leveraged the power of structural biology to help characterise effectors from pathogenic fungi predicted to act as Nucleoside-diphosphate linked to moiety-X (Nudix) hydrolase enzymes. I demonstrate that the AvrM14 effector from Melampsora lini (the causal agent of flax rust) and homologous rust fungal effectors are highly specific Nudix hydrolase enzymes capable of removing the protective 5’ cap structure from mRNA transcripts, rendering them susceptible to exoribonuclease decay (https://doi.org/10.1111/nph.18727). I also describe the discovery of a conserved Nudix hydrolase effector family in Magnaporthe oryzae (the causal agent of rice blast) and pathogenic Colletotrichum fungi. Structural determination and enzymatic assays revealed that these effectors hydrolyse inositol pyrophosphates, which plants use to monitor phosphate status and regulate starvation responses. Using qPCR and an innovative promoter-reporter system, I demonstrate that these effectors induce phosphate starvation responses in plants, consistent with the hydrolysis of inositol pyrophosphates. All together, my data advances our understanding effector function and the complex interplay occurring between pathogenic fungi and their plant hosts.

Biography: I received my Bachelor of Science degree from Flinders University in 2018. In my final year of undergraduate studies, I worked as a research assistant in Professor David Day’s group, aiding in studies of alternative oxidase from legumes. In the summer of 2018/2019, I visited ANU to complete a summer research project in the Williams lab. Intrigued by the field of plant-microbe interactions, I decided to join the Williams group for my Honours project in 2019, focusing on determining the enzymatic activity of the AvrM14 Nudix hydrolase effector. I continued in the Williams lab for my PhD in 2020, where I greatly expanded upon my initial research into Nudix hydrolase effectors.