My research focuses on parasitic plants, which I find to be the most intriguing of organisms. Parasitic plants are fascinating subjects because they possess unusual characteristics that reveal the extremes of plant growth and development. For example, the parasite haustorium has the capacity to attach to a host, invade host tissues to reach the host vascular system and form a connection that then serves as a conduit for transfer of host resources. An essential element of this process is the communication between host and parasite by which the haustorial cells navigate through the host tissue, suppress host defenses, and induce metabolic changes in the host to facilitate transfer of nutrients to the growing parasite. By elucidating the mechanisms underlying these host-parasite interactions I will identify processes that can be targeted to sever the continuity between parasite and host.
My research focus on basic parasite biology is necessitated by the fact that parasitic plants are Federal Noxious Weeds and their importation and movement within the US is restricted by law. Important parasite genera Orobanche, Phelipanche and Striga devastate crops in many parts of the world, and present a constant threat to become established in the US. Orobanche and Phelipanche species infest fields from North Africa to Eastern Europe and the Middle East, reducing yields and forcing farmers to stop growing susceptible crops. Striga species are a major constraint to cereal production in Africa where they cause annual yield losses exceeding $10 billion. The USDA imposes tight restrictions on importation of these species, so my research is confined to the plant quarantine facility in my laboratory. My long-term strategy for translating my research findings into practical control systems is to collaborate with overseas colleagues who can provide a field research component to our work and a link to farmers affected by parasitic weeds.
My interest in the host-parasite exchange of materials led me to also work on the parasitic plant genus, Cuscuta (dodders), which form exceptionally open haustorial connections with their hosts, resulting in the cross-species movement of macromolecules. My group was the first to report that messenger RNA (mRNA) from host plants can move into Cuscuta and continues to be a leader in characterizing the exchange of RNAs between plants.
The Parasitic Plant Genome Project (PPGP). This NSF-Funded project is a collaboration with colleagues at UC Davis, Penn State, and the University of Virginia. Together we are using a comparative framework of the family Orobanchaceae, which includes species representing the full range of parasitic dependence: a facultative parasite (Triphysaria versicolor), a photosynthetically-competent obligate parasite (Striga hermonthica), an obligate holoparasite [Phelipanche (=Orobanche) aegyptiaca], and their closest non-parasitic relative, Lindenbergia philippensis, which provides a point of contrast to the parasitic species. Transcriptome sequence data generated from these species 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. More information and data are available at http://ppgp.huck.psu.edu/.
Characterization of Mobile RNAs in a Host-Parasite Interaction. This NSF-funded project is studying Cuscuta pentagona, which has a remarkable ability to communicate with its host plants. During parasitism it develops a haustorium, which penetrates the host, establishes vascular connections, and serves as a conduit for obtaining water and nutrients from the host. This is all the more striking because our research has demonstrated the movement of specific messenger RNAs (mRNAs) from the host into Cuscuta. The project is investigating mRNA trafficking in the host-parasite system, focusing on tomato and Arabidopsis as model host species. New mobile mRNAs are being identified and characterized using next-gen sequencing of RNAs from parasite and host tissues.
Investigating the Basis for Germination Specificity in Orobanche. Among the most amazing abilities of parasitic plants is the host detection mechanism of the root parasitic Orobanchaceae. The seeds of these plants persist for years in the soil, only germinating when the root of an acceptable host plant grows near the seed. The germination signals are primarily strigolactones (although other compounds exuded from host roots may be involved), but the mechanism by which this signal is perceived by the parasite remains unknown. Our project is funded by BARD (US – Israel Binational Agricultural Research and Development Fund) with the goal of elucidating the basis for germination specificity in Orobanche species. Working with our collaborators in Israel, we are applying RNA-seq approaches to investigate the genetic differences between two closely related species, O. cumana and O. ceruna, that differ in host preference and in response to specific germination stimulants.
Ph.D., Horticulture, Purdue University, 1994
M.S., Plant Physiology, University of Minnesota, 1986
B.A., Biology, Concordia College, 1982