Dissecting molecular mechanisms of disease in the wheat pathogen, Parastagonospora nodorum

Abstract

Dissecting molecular mechanisms of disease in the wheat pathogen, Parastagonospora nodorum

Parastagonospora nodorum is a wheat specific pathogen that causes annual losses to the Australian wheat industry in excess of $100 million AUD. This necrotrophic fungus kills the host tissue generating necrotic lesions within which fruiting bodies develop, spreading spores and continuing the disease cycle. This polycyclic infection cycle leads to field epidemics resulting in the losses to growers. Sporulation and virulence are the two crucial aspects for disease development in the P. nodorum-wheat pathosystem and form the basis of this project.

A forward genetics approach was employed to discover novel mechanisms by which P. nodorum facilitates infection on wheat. A library of random P. nodorum insertion mutants was generated, and subsequently screened for gain and loss of virulence phenotypes on non-susceptible and susceptible wheat cultivars. From a library of 950 transformants seven displayed a consistent avirulent phenotype on the susceptible wheat cultivar. To identify the disrupted loci leading to avirulence, genomes of the seven avirulent P. nodorum strains were sequenced elucidating a Catechol-1,2-dioxygenase and a Copper dependent amine oxidase.

To complement the virulence investigation, a combined transcriptomics and metabolomics approach was employed to decipher sporulation in this pathogen. This is of particular interest as the canonical sporulation pathways in other, model fungi, were previously shown to be not applicable in P. nodorum. A differential gene analysis of fungal material collected at critical developmental time points identified several key genes involved in initiating a sporulation cascade. Notably, a WetA homolog was identified, along with an uncharacterised Aquaporin-like protein and a Pr1-like protein. Metabolomics and subsequent sporulation assays revealed a polyamine pathway plays an integral role in initiating and coordinating asexual development of P. nodorum.