Regulation and cell biology of secondary metabolite production in Fusarium graminearum and Fusarium pseudograminearum

Abstract

1 AbstractAscomycete fungi have the potential to produce a vast array of secondary metabolites, which are metabolites not required for normal growth and development. In any one species there is typically the potential for production of upward of fifty of these compounds. Many fungal secondary metabolites are used as medicines (e.g. penicillin or cyclosporine), or are of importance due to their toxicity in humans or animals (e.g. aflatoxins), or because they are virulence factors during crop plant infection (e.g. deoxynivalenol). Despite the vast potential encoded in ascomycete genomes, the vast majority of fungal secondary metabolites are yet to be discovered. This is in part due to our lack of understanding of how the production of these compounds is regulated. Moreover, even for the compounds we do know, we are just beginning to understand the complex interaction of external stimuli, signalling pathways, cellular and developmental biology that leads to their production. In this thesis, biological insights into these aspects of two fungal secondary metabolites, deoxynivalenol (DON) and fusatin are provided.In chapter II a high-throughput fluorescence activated cell sorting (FACS) based mutant screen was developed and the regulation of DON production in Fusarium graminearum was analysed. DON is an economically very important mycotoxin, as it is the most common contaminant of wheat, barley and corn worldwide. It is produced by plant pathogenic filamentous fungi of the Fusarium family, which can cause Fusarium head blight as well as Fusarium crown rot. During plant infection, DON is an important virulence factor and it can be toxic for humans and animals. The regulation of DON production is not yet fully understood. To identify regulators, a mutant screen was developed using FACS to allow high throughput screening, coupled with whole genome sequencing to identify mutations.Segregation analyses were performed to determine the mutation causing the phenotype.The mutant screen identified an adenylyl cyclase allele, which resulted in production of DON under normally repressive conditions. In addition, the mutant developed cellular structures associated with toxin production under repressive conditions. The levels of the fundamental second messenger cAMP, which adenylyl cyclases produce, were increased in the identified mutant, suggesting it might be a gain-of-function adenylyl cyclase mutant. This mutant screening methodology can be adapted to identify regulators of different secondary metabolites as well as to identify mutants overproducing yet unknown secondary metabolites. Abstract 2In chapter III the cell biology of DON production in Fusarium graminearum was elucidated with quantitative super resolution microscopy. During the last five years the first insights into the cell biology of DON production were gained, indicating complex cell biological mechanisms. During toxin production, F. graminearum develops endoplasmic reticulum proliferations, called toxisomes, at which two DON biosynthesis enzymes, TRI1 a...

FoEG1, a secreted glycoside hydrolase family 12 protein from Fusariumoxysporum, triggers cell death and modulates plant immunity

“…However, not all fungal CWDEs have been conclusively shown to be involved in pathogenicity and virulence. For example, the deletion mutant strain of a pectate lyase gene PelA from Fusarium graminearum does not show attenuated virulence during the infection of wheat coleoptiles (Blum, 2017). CWDEs secreted by plant-pathogenic fungi are important for host infection and colonization.…”

A Verticillium dahliae Pectate Lyase Induces Plant Immune Responses and Contributes to Virulence

“…Not all fungal pectate lyases have been conclusively shown to be involved in pathogenicity and virulence. For example, PelA (a pectate lyase gene form Fusarium graminearum ) knock-out strains did not show attenuated virulence during the infection of wheat coleoptiles ( Blum, 2017 ). The expression of VdPEL1 was most significantly up-regulated during the infection stage (1.5–3 days) before dropping sharply to the initial level ( Supplementary Figure S5 ).…”