Plant-Plant Recognition: Chemistry-Mediating Host Identification in the Scrophulariaceae Root Parasites

As little as a year ago we reviewed our understanding of the chemistry mediating host recognition in the parasitic angiosperms ( 8 ). Although a number of haustoria-inducing factors had been found, it was clear that the underlying mechanism for this plant-plant interaction was not understood. This paper reviews the identification of 2,6-dimethoxy- p -benzoquinone (2,6-DMBQ) in Sorghum roots as a haustoria-inducing principle for Striga asiatica (Scrophulariaceae). The unique timing events required for Striga parasitism suggest that haustorial induction is mediated through degradation of host root surface components by the parasite's enzymes. Quinones, such as 2,6-DMBQ, would be released and used as recognition signals. This kind of biological recognition may be common to many of the Scrophulariaceae and, in fact, could be a general mechanism for plant-plant interaction.