Fungi have a major impact on agriculture, some as disease-causing agents and others as disease-suppressing (biocontrol) agents. My laboratory uses the tools of molecular biology to study the molecular determinants in these fungi that allow pathogenic or disease-suppressing ability. In studying plant pathogens, we are interested in the ability of a fungus to specifically recognize and react to compounds uniquely produced by its host plant. The plant-pathogen interaction on which we focus is that between garden pea (Pisum sativum) and the fungus, Nectria haematococca MPVI (anamorph: Fusarium solani), the causal agent of pea stem and root rot.

We are studying two fungal responses to flavonoid compounds produced by pea. The first is the production of an enzyme (pisatin demethylase), which detoxifies pisatin, a fungitoxic isoflavonoid produced by pea in response to infection. We are studying a transcriptional regulator that induces expression of the gene encoding pisatin demethylase in response to pisatin. A second response is one of germination in response to pisatin and certain nontoxic flavonoids exuded by pea roots. This response is likely to be an early event in host recognition. We are studying the intracellular mechanisms by which these flavonoids are recognized and germination is induced. Pharmacological evidence demonstrates that cAMP-dependent protein kinase may be involved in the signal pathway.

A second focus of my laboratory involves studying the role of antibiotics produced by the fungus, Gliocladium virens, in suppressing damping-off disease caused by the fungus, Pythium ultimum. Gliotoxin is one antibiotic made by this biocontrol agent. Through mutational analysis, we have demonstrated that this antibiotic does contribute to biocontrol activity. We are presently cloning genes required for gliotoxin biosynthesis and resistance to study their regulation and allow their manipulation. Ultimately, we hope to improve the range and effectiveness of G. virens biocontrol activity through enhancement of gliotoxin production.