Chapter 1 Interactions between Agaricus bisporus and the pathogen Verticillium fungicola

The interaction between Agaricus bisporus and Verticillium fungicola may be the most economically significant interaction between two fungi. Work described in this chapter covers diverse aspects of the biology and molecular interaction of the host and pathogen and has established a robust baseline for future study of a pathogenic system involving two members of the same kingdom. Pathogen variability has been assessed, and specific genotypes important to major mushroom-producing countries have been characterised. This has enabled representative isolates to be identified for use in this study. A wide range of cell-wall-degrading enzymes from V. fungicola have been identified, and principal component analysis showed a complex correlation between enzyme production and symptom expression. It is likely that some, or indeed many of these enzymes play a critical role in the pathogenicity of Verticillium. Although it is generally accepted that A. bisporus has a relatively narrow genetic base, our work, and that of other groups, has shown that variability in host tolerance to infection with V. fungicola exists to a large extent to justify a detailed study to exploit it. We have developed transformation technologies for the mushroom A. bisporus (Challen et al., 2000; Leach et al., 2004; Foster et al., 2004b; Burns et al., 2005, 2006), its pathogen V. fungicola (Amey et al., 2002, 2003) and other pathogenic fungi (Rogers et al., 2004; Gewiss-Mogensen et al., 2006). Recent advances in gene suppression technologies for the host include deployment of anti-sense and RNAi hairpin constructs to down-regulate endogenous A. bisporus genes (Burns, 2004; Heneghan et al., in press). Similarly gene knockout methodology has been established for the pathogen V. fungicola (Amey et al., 2003;Foster et al., 2004a). An extensive range of genetic resources have been established, which include: V. fungicola pathogenicity simulated cDNA library (mushroom cell wall (MCW) agar), numerous A. bisporus fruiting cDNA libraries (macro-arrayed), host (A. bisporus)-pathogen (V. fungicola) lesions infection SSH libraries (forward and reverse subtractions for up- and down-regulated mushroom genes) and macro-arrayed cDNA infection library, genomic DNA libraries for A. bisporus and other homobasidiomycete mushrooms, EST fungal-fungal interaction database; transformation and expression vectors designed specifically for Agaricus and Verticillium, and vectors to expedite cloning of fragments for gene silencing experiments. The resources now in place will enable us to determine, in a systematic manner, the impact of gene expression on the disease phenotype. This work provides platform technologies for alternative methods of disease control, reduced pesticide use and sustainable crop production. Investigations into this model fungal-fungal interaction will also provide information on the research and development of fungal biological control agents of fungal plant pathogens. © 2008 Elsevier B.V. All rights reserved.