Molecular Bases of Interaction Between Soybean Cyst Nematode and Antagonistic Soil Fungi

Abstract

A diverse community of soil fungi antagonize the economically consequential plant-parasitic soybean cyst nematode (SCN; Heterodera glycines) through direct parasitism, secretion of bioactive secondary metabolites, or a combination of both. Characterizing fungal antagonism towards SCN eggs, and conversely the responses of SCN to fungal antagonism, may help better understand the dynamics, mechanisms and targeted molecular processes involved, and ultimately lead to the formulation of more effective fungal biocontrol agents or biopesticides. Chapter 2 describes fluorescence microscopic observations and transcriptomic expression patterns determined from SCN eggs placed in co-culture on top of fungal cultures of Pochonia chlamydosporia 123 and Ilyonectria sp., sampled at multiple timepoints (1, 3 and 5 days) of interaction. The non-specific cellulose and chitin stain Calcofluor White M2R and DNA-intercalating apoptosis stain propidium iodide were used for fluorescent labeling of fungal structures and nematode apoptosis within SCN eggs, respectively. Using this combination of microscopic and transcriptomic approaches, I characterized potential differences in interactions between SCN eggs and the two fungal isolates in the framework of established modes of pathogenicity of fungal pathogens of plants (i.e. biotrophy and necrotrophy), as well as uncover genes potentially involved in the perception and immune responses by SCN against these fungal antagonists. Chapter 3 pursues the chemical basis of antagonism of two Ilyonectria field isolates (Ilyonectria sp. and E413-17) using a bioactivity-guided fractionation approach to procedurally identify samples for purification and characterization. This chapter also examines candidate genes in early timepoints of SCN lifecycle for their suitability as housekeeping genes in qPCR applications for future studies to examine genes of interest.