The Fate of Peripheral Vesicles in Zoospores of Phytophthora cinnamomi During Infection of Plants

Abstract

Motile zoospores play a major role in the infection of plant roots by the dieback fungus, Phytophthora cinnamomi [22]. Under moist conditions, the fungus releases vast numbers of zoospores into the soil. The zoospores can be transported passively over considerable distances by underground water, thereby facilitating the spread of the pathogen. Once in the vicinity of a root, the zoospores exhibit positive Chemotaxis to the root exudate and as a result rapidly accumulate along the zone of cell elongation just behind the root tip. Contact with root surface components triggers the encystment of the zoospores. Fucosyl residues on the root surface have been implicated in this recognition step [10] but so far no fucosyl-containing molecules which can trigger encystment have been isolated from the root surface. Encystment entails the rapid loss of motility and shedding of flagella, exocytosis of peripheral vesicles, change in cell shape and, after 5–10 min, formation of a microfibrillar cell wall. This is followed, about 20 min later, by germination and subsequent invasion of the root tissue.