Evolutionary Gain and Loss of Function in Parasitic Plant Genomes

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PI: James Westwood (Virginia Polytechnic Institute and State University)CoPIs: Claude dePamphilis (Pennsylvania State University), Michael Timko (University of Virginia), and John Yoder (University of California - Davis) Senior Personnel: Eva Collakova and Lenwood Heath (Virginia Polytechnic Institute and State University) and Aaron Mackey (University of Virginia)The evolutionary transition from autotrophism to heterotrophism by parasitic plants is an extraordinary example of adaptive plant biology. It is associated with striking morphological adaptations, such as the development of a haustorium, and physiological changes that enable the parasite to enter host tissue and redirect host nutrients to the parasite. This project will build on a prior NSF-supported study that sequenced expressed genes from key life stages of three species that span the spectrum of plant parasitism: a facultative parasite (Triphysaria versicolor), a photosynthetically-competent obligate parasite (Striga hermonthica), and an obligate holoparasite [Phelipanche (=Orobanche) aegyptiaca]. Sequences were also generated from the closest non-parasitic relative, Lindenbergia philippensis, which provides a point of contrast to the parasitic species. These data will be used, along with metabolite profiles from key stages of parasite and host tissues, to identify gene and metabolic networks that function uniquely in parasitic plants. The project aims to identify and characterize genes that are essential for haustoria function in connecting to host tissues and extracting host nutrients such as amino acid and sugar transporters and transcription factors. Candidate genes will be characterized through a series of analyses including detailed temporal and spatial expression, functional knockout by trans-specific gene silencing, and direct gene knockout or overexpression in the parasite species. Analysis of transgenic parasites with modified expression of specific genes will reveal new patterns of gene and metabolic regulation that will reveal how genes have evolved to enable parasitism in plants. The broader impacts of this research derive from understanding how plant genes evolve under the tight constraints of parasitic interactions and from the large impact that certain parasitic species (e.g. Striga and Orobanche spp.) inflict on agriculture in developing nations of Africa. The project will emphasize student training that bridges diverse fields of bioinformatics and applied agriculture. Project personnel will collaborate with colleagues in Morocco and Kenya to translate basic research findings from the project into progress in control of parasitic weeds.Parasitic weeds are devastating agronomic pests worldwide and a significant constraint to agricultural productivity and food security in developed and developing countries alike. In addition to providing basic cellular and metabolic scale data on this group of related plants that encompass an enormous breadth of morphological and physiological diversity, the project will contribute directly to the design of novel strategies for the control of these noxious pests. The potential positive and lasting impact of such advancement on crop production, food security and human health cannot be overemphasized. As the global threat from parasitic weeds expands, the need for trained individuals who understand their biology will be accentuated. Recognizing this need and the paucity of trained personnel at all levels in the US, this project will train graduate and post-doctoral students not only in the laboratory at their home institutions, but through participatory field experiences internationally. These 9-day laboratory/field practicals in International Parasitic Plant Research will be conducted in the 2nd and 3rd years of this project and will take personnel from the four US institutions to Morocco or Kenya to work with collaborators, observe Phelipanche, Orobanche and Striga species in the field, conduct workshops, and gain first-hand knowledge of the challenges faced by agriculturalists dealing with parasitic weeds. It will also help disseminate project findings to African researchers to assist in their research activities. Integrated with the science, students will engage in study of cultural, socioeconomic, and geographical aspects of science and agriculture in developing countries. All sequence data will be deposited at GenBank and data and tools generated in the project will be accessible through the project website and through the iPlant Collaborative. Metabolomic data will be deposited through emerging public repositories such as MetabolomeExpress and DROP Met. Striga and Phelipanche are on the Federal Registry of Noxious Weeds and current regulations restrict the importation and handling of these seeds except by laboratories holding valid USDA/APHIS PPQ 526 permits for quarantined plant seeds. Parties interested in obtaining germplasm used or generated in this project are encouraged to first contact USDA/APHIS regarding how to obtain permission to work with these species.