Exploration of plant and pathogen signalling during the biotrophic to necrotrophic switch in hemibiotrophic interactions

Abstract

Hemibiotrophic pathogens are a group of pathogenic microbes that cause a significant reduction in plant growth and fitness, impacting yield within agronomic systems. Pathogens within this group possess a complicated lifestyle characterised by an initial symptomless biotrophic phase during which the pathogen feeds off of live plant tissue, followed by a necrotrophic phase when the pathogen kills plant tissues and feeds off of the remaining nutrients. Between these two phases is a switching phase, hereafter termed the biotrophic to necrotrophic switch (BNS) phase. The timing and pathways controlling this phase are poorly understood. The interaction between plants and pathogens during each phase of hemibiotrophic infection is mediated, in part, by signals passed from the pathogen to the host and by plant-based defence signalling pathways directed back at the invading pathogen. A large portion of pathogen signals transferred to the host during infection are small secreted proteins termed ‘effectors’ that function to manipulate plant defences and host cellular processes. In the plant host, defence signalling pathways comprise recognition proteins, internal signalling compounds including phytohormones, and downstream defences including secondary metabolites and callose deposits. To date, only a handful of pathogen effectors and host defence signalling pathways have been characterised in model hemibiotrophic interactions. Of these, even fewer have identified pathogen effectors and host defence signalling pathways have been shown to regulate a specific phase of hemibiotrophic infection.

Taken together, my thesis investigates pathogen effectors that play a role during hemibiotrophic disease progression and the host defence signalling pathways induced in response. My thesis also identifies the putative control mechanisms regulating pathogen effectors and the BNS in two key hemibiotrophic pathogens. The knowledge and resources generated in my thesis are important to further our understanding of both model and non-model hemibiotrophic interactions. Furthermore, my work provides the platform to better understand root hemibiotrophic pathogenesis. The knowledge gained from this thesis will be important in future to improve disease resistance and provide novel targets to control hemibiotrophic disease.

Date of Thesis submission	2021
Original language	English
Awarding Institution	Western Sydney University
Supervisor	Jonathan Plett (Supervisor), William S. Cuddy (Supervisor) & Henrik U. Stotz (Supervisor)