My program investigates the cell biology of plant pathogens, especially of fungal and bacterial pathogens.
Over the years my research program has emphasized various aspects of fungal cell biology, especially of fungi that cause plant diseases. These studies have been directed at investigations into the mechanisms by which fungi use leaf surface characteristics to sense the right time and place to infect their host. Toward this, micro- and nanotechnology has been used to fabricate devices, and surfaces that mimic plant features, to interrogate fungal cell function. Highlighted discoveries of our studies are that: the bean rust pathogen, Uromyces appendiculatus, uses topographical leaf surface features to guide the pathogen to plant stomata (pores) where it then senses a 0.4 to 0.8 micrometer high topographical features which triggers it to develop specialized infection structures needed to enter the host plant; Colletotrichum graminicola, the incitant of anthranose disease of grasses, require at least 4 micrometers of surface area to develop similar infection structures. More recent research activities involve studying colonization of grape xylem elements by the pathogenic bacterium, Xylella fastidiosa, the causal agent of Pierce's Disease of grape, as well as other bacterial pathogens, e.g., Clavibacter michiganesis, Xanthomonas campestris, and Agrobacterium vitis of various crop plants. Because the xylem vessel environment within a living plant can not be readily viewed, similar fabrication technologies were used to create microfluidic chambers that mimic plant xylem vessels where the bacteria can be studied temporally and spatially. We have demonstrated that the bacteria move against the flow of xylem sap through the extension and retraction of hair-like type IV pili, and that they develop large aggregates of cells within biofilms.