The Striga Project-

Current Project Members:

Yue Liu, Emily Pinto

It has been estimated that 1% of all flowering plants are parasitic. Witchweeds (Striga spp.) and other parasitic plants are a major constraint on grain production throughout the developing world.The survival of obligate parasites, such as Striga asiatica, is dependant on successful host detection and attachment. Host attachment occurs via a specialized organ known as the Haustorium. Such developmental transitions are driven by host derived signals (or Xenognosins) in a variety of parasites. Ongoing work in the Striga project explores the origin of these xenognosins as well as the mechanisms by which they are perceived. Such studies explore organogenesis in plants as well as the evolutionary divergence between the parasitic and non-parasitic paradigms. These studies may also lead to better mechanisms for crop regulation reducing the agricultural impact of parasitic weeds.

Haustorium Organogenesis: Host attachment occurs via formation of a specialized attachment organ known as the haustorium. The Haustorium is characterized by swelling of the root tip and the formation of specialized hairs at the root tip. Hastorium formation is induced by p-benzoquinones with a redox range between 0 to -250mV suggesting both oxidation and reduction are required for inducing haustorium formation. Andrew Palmer is currently exploiting this redox chemistry to sythesize inhibitors for the purposes of isolating the receptor for quinone perception. Meanwhile Yue Liu is developing a subtraction library to explore the genes regulated during haustorial organogenesis

Left: SEM image of haustorium formed in Striga asiatica attached to a corn root. From: Parasitic Weeds in Agriculture

Regulation of Haustorium Formation: Following germination seedlings of Striga asiatica begin producing hydrogen peroxide exploiting the innate defense responses of prospective host roots by reacting with peroxidases and phenols to generate haustorial inducing quinones. Given the role of reactive oxygen species (ROS) as secondary messengers however this seemed an unlikely mechanism for generating signals. Our studies (Andrew Palmer, John Keyes, and Lizhi Liang) have established that hydrogen peroxide production is downregulated by the perception of the very signals which they participate in the synthesis of. We are currently mapping out regulation of this oxidants production at the both the enzymatic and genetic levels.

Right: Day old seedlings of S. asiatica stained with the cell permeable H2O2 reactive dye H2-DCFDA. Over 15 minutes fluorescence accumulates in untreated seedlings (top). Seedlings treated for 2hr with the haustorial inducing quinone DMBQ (2,6-dimethoxybenzoquinone) shows little to no fluorescence accumulation. (In Preparation)