EAGER: Striga Virulence Effectors: Keys to Halting Parasitic Witchweeds

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Parasitic angiosperms are noxious and persistent pests in farmers' fields and serious constraints to crop productivity. The "witchweeds", members of the genus Striga, are particularly devastating since their primary hosts include the major cereals (maize, sorghum, rice and millet) and grain legumes that are dietary staples worldwide. How parasitic weeds and Striga species in particular recognize their potential hosts and overcome the innate defense systems are not known. Using the interaction of cowpea (Vigna unguiculata), an important food and forage legume, with Striga gesnerioides, this project seeks to identify parasite-derived effectors and virulence proteins that enter host cells, specifically altering their structure and function and suppressing the defense response mechanism at various levels, enabling infection and parasite ingress to occur. Novel, in planta functional screens will be used to identify candidate effectors from Striga that are directly or indirectly recognized by race-specific resistance proteins in cowpea leading to activation of a hypersensitive response at the point of infection and associated downstream defense responses. These functional screens are complemented by comparative transcriptome sequencing in compatible and incompatible host-parasite association and in silico analysis aimed at identifying candidate virulence effectors through race-specific gene expression signatures. The outcomes of this project will provide novel insights into the mechanisms by which parasitic angiosperms identify and parasitize their hosts and how hosts block such attack. The negative impact of parasitic plants on crop productivity increases globally each year and their potential for affecting domestic agriculture looms larger as the movement of seed resources expands globally. The outcomes of this work will contribute directly to the development of strategies to improve crop security by providing targets for manipulating pest resistance responses of crop plants. In addition these studies provide new educational, research, and training opportunities for US students on the African continent.