Parasitic Plant-Host Interactions in the Rhizosphere

A wide number of organisms specialized in parasitizing plants. Plants are not exceptions; certain plant species evolved as parasites of their own kind. Indeed, flowering plants evolved parasitism independently at least 12 times, in all cases developing a unique multicellular organ called the haustorium that forms upon detection of haustorium-inducing factors derived from the host plant. This organ penetrates into the host stem or root and connects to its vasculature, allowing exchange of materials such as water, nutrients, hormones, proteins, nucleotides, pathogens, and retrotransposons between host and parasite. In particular, parasitic plants in the genus Striga (Orobanchaceae family), commonly known as witchweeds, cause major crop losses in sub-Saharan Africa and pose a threat to agriculture worldwide. To understand how parasitic plants perceive hosts and develop the haustorium, we have established a new model parasitic plant system, using an Orobanchaceae plant Phtheirospermum japonicum, which enables forward/reverse genetics for functional analysis of plant parasitism. Genomic and transcriptomic studies combined with genetic and live-imaging analyses revealed key components in haustorium development. By focusing on the formation and function of the haustorium in P. japonicum roots, we began to understand how the parasitic plant interacts with the host plant in rhizosphere. I will report new components in haustorium development and a hypothesis for the parasite evolution.