Evolutionary Gain and Loss of Function in Parasitic Plant Genomes

One of the largest and most economically important lineages of parasitic plants, Orobanchaceae, includes members ranging from facultative to obligate holoparasitic species.  Parasitic members of Orobanchaceae growing in Africa and the Mediterranean include the devastating agricultural pests, witchweed (Striga) and broomrape (Phelipanche). The Parasitic Plant Genome Project (PPGP - http://ppgp.huck.psu.edu) is taking a comparative evolutionary approach to understanding parasitism in the Orobanchaceae.  The project has generated nearly 2 billion Illumina and 454 expressed sequence tags from a facultative parasite (Triphysaria versicolor), a photosynthetically competent obligate parasite (Striga hermonthica), and an obligate holoparasite (Phelipanche aegyptiaca).  The sequenced and de novo-assembled Illumina transcriptomes represent all life stages from seed conditioning to flowering plus an enhanced view of the parasite-host interface afforded by laser microdissection.  Results thus far include surprising conservation of the chlorophyll synthesis pathway in the non-photosynthetic Phelipanche, host-specific gene expression by the generalist Triphysaria and a case of horizontal transfer of a legume specific gene into Phelipanche species. 

The next phase of the project aims to identify genes associated with parasitism in plants and also to characterize primary metabolism and nutrient transporters in a comparative evolutionary context, that is, by making comparisons across varying demands for host resources.  Using functional transcriptomics, high-resolution tissue sampling, metabolomics, parasite transformation and other molecular techniques, we aim to further our understanding of parasitism in plants.  In addition, we are establishing collaborations in countries affected by the weedy Orobanchaceae to train scientists in developing countries and deepen our understanding of parasitic plants as agricultural pests.