How fungal pathogens communicate with plant cells and cause disease

Abstract

Warmer atmospheric conditions are creating a climate increasingly suitable for the spread of crop pathogens and pests, significantly reducing crop yields. Fungal pathogens are responsible for approximately 15% of crop losses; therefore, an enhanced understanding of how fungal plant pathogens communicate with plant cells and cause disease is necessary to improve global food security. Zymoseptoria tritici, the main causal agent of Septoria tritici blotch in wheat, and Fusarium graminearum, the main causal agent of Fusarium Head Blight in small-grain cereals, are fungal pathogens of global importance based on both scientific and economic impact. The interactions of these pathogens and their hosts is relatively understudied. Therefore, the aim of this project was to develop novel approaches to understand the relationship of Z. tritici and F. graminearum with wheat during infection. The processes which determine whether successful infection is established within the host (compatible interaction) or not, whereby host defence is successful and no infection is established (incompatible interaction), are still not fully understood. Consequently, the present study aimed to produce Z. tritici metabolic biosensors to determine the fungal response to the host in both compatible and incompatible interactions. However, the results demonstrated that higher expression of the biosensor construct, mitroGFP2-Orp1, is needed for this tool to be of future use. Unlike Z. tritici, F. graminearum can travel intracellularly in the host once successful infection has been established. This is facilitated by pit-fields (PFs) which are abundant in plasmodesmata (PD). Thus, a series of approaches were developed to investigate the F. graminearum-PD interaction at both the cellular and molecular levels. A high-throughput wheat coleoptile infection assay was adapted to image PD when infected with the wildtype PH-1, and mutant GT2 and MAP1 strains. Particle bombardment was used to generate stable wheat plasma membrane (PM) reporter lines, utilising the genes AtLTI6b and ZmROP7, for live-cell imaging of PFs during infection. However, no or low expression of the PM constructs resulted in this experiment being unsuccessful. Finally, bioinformatics analyses were used to identify wheat proteins involved in PD-permeability control, AtBG_PPAP and AtPDLP orthologs, for use in virus-induced gene silencing experiments to assess how F. graminearum hyphal progression is regulated within the host. The present study has provided novel datasets, approaches and tools, which have the potential to improve not only Z. tritici and F. graminearum research, but that of a multitude of fungal-host interactions as well as crop protection strategies.