XVI International Botanical Congess
Little is known about molecular-level responses of plants to attack by parasitic angiosperms. The influence of Orobanche parasitization on regulation of host defense-related genes is being studied using transgenic plants containing promoter: GUS fusions and by northern hybridization analysis. Parasitized tobacco roots show increased expression of genes known to be induced by wounding alone (hmg 1) or in association with local response to ingress by specific pathogens (hmg2, PAL, CHS). By contrast, a gene (PR1a) expressed in associated with systemic induction following virus or elicitor treatment, but not wounding, was not induced by Orobanche. These results suggest that host defense responses to the parasite may be mediated primarily by physical damage to root tissue caused by penetration of the Orobanche haustorium.