XENOGNOSIN METHYLATION IS CRITICAL IN DEFINING THE CHEMICAL-POTENTIALGRADIENT THAT REGULATES THE SPATIAL-DISTRIBUTION IN STRIGA PATHOGENESIS

Striga asiatica (Scrophulariaceae) is a parasitic plant requiring a ho st-derived signal, xenognosin, to initiate a cascade of events necessa ry for the establishment of host contact. By attempting to model the d istribution of the xenognosin around the host, the activity of the sig nal is shown to be strongly dependent on the presence of another compo nent in the host exudate. Surprisingly this component, characterized a s [(8'Z,11'Z)-8',11',14'-pentadecatriene]resorcinol, is structurally r elated and shares the same biosynthetic pathway as the xenognosin. Thi s compound is shown to function as an antioxidant and its ability to e nhance the activity of the xenognosin is consistent with its ability t o extend its lifetime in the exudate. This endogenous antioxidant acti vity is required to explain the spatial sensing in the establishment o f the host-parasite interface and its characterization provides insigh t into how chemical potential may be regulated within and around plant tissues.