Recognition of host plants by parasitic angiosperms
We are interested in understanding how plants communicate via chemical signals in the environment. We are particularly focused on the genetic mechanisms governing the interaction of parasitic Angiosperms and their plant hosts. Parasitic plants are interesting because their growth, development, and physiological behaviors are modified in response to molecular signals exuded from neighboring plants. In addition, the study of parasitic plants is important because of the agricultural devastation caused by several of the more pernicious weedy species. For example, the parasitic weed Striga is estimated to infect two thirds of the cultivated lands in sub-Sahara Africa where it can cause complete yield loses in critical staples such as maize, sorghum, millet, and broad beans. The FAO estimates that the lives of over 100 million Africans are negatively affected by this single plant pathogen alone.
Because parasitic weeds are difficult to study for both biological and regulatory reasons, we are employing an experimentally tractable model species, Triphysaria. Triphysaria is useful for these studies because it is a facultative parasite that can be grown either in the presence or absence of hosts plants, it is a simple diploid amenable to classical genetic manipulations, and it infects Arabidopsis roots by processes that can be readily monitored in vitro. Because both the host (Arabidopsis) and the parasite (Triphysaria) are amenable to genetic analysis, this is a simple system for identifying genetic loci governing plant parasitism.
Triphysaria is a broad host range parasitic plant that recognizes and infects a broad spectrum of monocot and dicot hosts. There is, however, and important exception to the apparently indiscriminate host range of Triphysaria; Triphysaria only rarely parasitize their own roots or those of closely related species. We are currently investigating the genetic basis of this novel, vegetative, self-recognition system.
Current experiments are directed towards understanding the molecular mechanisms governing the early steps in host root recognition and invasion. We are taking a transcript profiling strategy to distinguish genes specifically active in parasitic species exposed to host root factors. Triphysaria variants incapable of developing invasive haustoria in response to specific signal molecules are being used to define genetic components. We are also screening Arabidopsis populations for mutations that alter host signals recognized by Triphysaria. By identifying the genetic factors in both the host and parasite that are required for successful infections, we hope to identify candidate targets for engineering host resistance.