The Use of Arabidopsis to Study Interactions between Parasitic Angiosperms and Their Plant Hosts

Abstract

Parasitic plants invade host plants in order to rob them of water, minerals and nutrients. The consequences to the infected hosts can be debilitating and some of the world’s most pernicious agricultural weeds are parasitic. Parasitic genera of the Scrophulariaceae and Orobanchaceae directly invade roots of neighboring plants via under- ground structures called haustoria. The mechanisms by which these parasites identify and associate with host plants present unsurpassed opportunities for studying chemical signaling in plant-plant interactions. Seeds of some parasites require specific host factors for efficient germination, thereby insuring the availability of an appropriate host root prior to germination. A second set of signal molecules is required to induce haustorium development and the beginning of heterotrophy. Later stages in parasitism also require the presence of host factors, although these have not yet been well characterized. Arabidopsis is being used as a model host plant to identify genetic loci asso- ciated with stimulating parasite germination, haustorium development, and parasite support. Arabidopsis is also being employed to explore how host plants respond to parasite attack. Current methodologies and recent findings in Arabidopsis – parasitic plant interactions will be discussed. Introduction While an oft-taught dogma in biology curricula is that plants differ from animals in being able to generate organ- ic nutrients from inorganic raw materials and sunlight, some plants obtain nutritional resources by feeding off other plants. For example mistletoes, the arboreal para- sites closely associated with Christmas, are dependent on host plants for water, minerals, and to varying degrees, fixed carbon (Parker and Riches, 1993; Press and Graves, 1995). Like other parasitic plants, mistletoes directly invade their hosts and rob them of nutritional resources through specialized organs called haustoria (Kuijt, 1969). The direct attachment and penetration of host tissues make parasitic plants distinct from saprophytic plants, like Mono