Parasitic angiosperms, semagenesis and general strategies for plant–plant signaling in the rhizosphere

Abstract

In addition to their roles in eukaryotic defense and development, reactive oxygen species (ROS) have recently been identified as critical for host attachment by the parasitic angiosperms. In a process known as semagenesis, ROS generated at the root tip of Striga asiatica (L.) Kuntze (Scrophulariaceae) function together with host peroxidases to oxidize monolignols at the host root surface. As a result, para-benzoquinone products accumulate as both necessary and sufficient components for inducing development of the host attachment organ, the haustorium. This event constitutes the critical vegetative/pathogenic transition in the parasite. New evidence is presented that semagenesis occurs broadly in plant-plant signaling. Eudicotyledenous seedlings are more sensitive to the xenognostic benzoquinones than monocots, but general root development, including root elongation, root hair initiation and root hair growth, is impacted in both clades. Specific inhibitors of haustorial development in S. asiatica also inhibit benzoquinone-mediated root development in the non-parasites. These results suggest a common mechanism for benzoquinone perception. Semagenesis enriches our understanding of the mechanisms available for small-molecule underground information exchange among plants. Critical differences in this process, as used by parasitic plants, are beginning to emerge and point towards new strategies for managing parasitic angiosperms in agricultural settings.