The Regulation of Surface Responsive Genes in Blumeria graminis f. sp. hordei

Abstract

Powdery mildew of barley is caused by the ascomycete pathogen Blumeria graminis f. sp. hordei (Bgh). Bgh is economically important throughout the world, causing crop losses varying between 5 to 20 % and in extreme cases as much as 60 %. Bgh is an obligate biotroph, relying on its host for growth and reproduction. This characteristic has hindered attempts to carry out biochemical and molecular biological analysis. Previous work had highlighted differential gene expression during Bgh development on surfaces other than the host. Consequently, this thesis had three aims. The first attempted to elucidate the nature of this gene expression. Work listed within includes studies of Bgh morphological development on the host barley, wheat, cellulose membrane, and glass. Additional studies included the assessment of gene expression, via RT-qPCR, on glass surfaces enhanced with 1-hexacosonal (a synthetic C26 aldehyde known to spur Bgh development), 16-hydroxyhexadecanoic acid (a cutin monomer found within the barley leaf), as well as surfaces of differing hydrophobicity. Results collected reenforce the surface-dependent nature of gene regulation, and highlight how gene expression is determined by the integration of multiple signal inputs. The second aim of this thesis was the transformation of Bgh utilising Agrobacterium tumefaciens. Efforts are discussed as are approaches for future work aimed at transforming this fungus. The final aim of the thesis aimed to lay foundations for work involving the assessment of 5‟-regulatory regions of genes showing clustered, and differential, expression on alternate surfaces. Utilising the phytopathogenic model fungus Magnaporthe oryzae (the causal agent of rice blast disease), 22 promoter regions were tested for their ability to drive GFP in this pathogen. 2 regions (for genes encoding a H4 histone and an aconitase) along with promoter regions selected for their conservation, were able to do so.