Semagenesis & Xenognosis: Translating the Molecular Dialogues of Host-Parasite Interactions Open Access

Palmer, Andrew George (2008)

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The sessile nature of plants has resulted in the coupling of basic developmental programs to a variety of external signals, as well as the evolution of an arsenal of small molecules with which to influence other organisms. These seemingly divergent concepts converge in the parasitic plants where host derived signals direct multiple stages of development. In the parasitic angiosperm Striga asiatica, the signals that regulate germination, host attachment, and shoot apical meristem development have been identified making this an ideal system for studying both the interface which defines interorganismal signaling events, as well as small molecule regulated development. Host attachment and the subsequent siphoning of nutrients is marked by the development of a specialized organ, unique to the parasitic plants, the haustorium. The signals which regulate this developmental transition are p-benzoquinones generated by the oxidation of host derived monolignols via reactive oxygen species (ROS) released by the parasite in a process known as semagenesis. This active process sharply contrasts with more traditional passive signaling events and raises several questions as to its origins and regulation. The studies herein have confirmed the localization, regulation, and source of semagenic ROS. Furthermore, they suggest a mechanism for the perception of the haustorial inducing quinones is conserved among non-parasites. These results confirm the critical importance of tight regulation over the signaling events at the host-parasite interface, further defines this new role for reactive oxygen, potentially provides new targets for limiting successful parasitism, and insights into the molecular origins of host detection and parasitism.

Table of Contents

1.5 A mechanism for the production of xenognostic quinones
1.6 Activity of xenognostic quinones
1.7 Evaluating and justifying a model for phenol oxidation to xenognostic quinones
1.8 Refining a model for the oxidation of host root surfaces
1.9 The many faces of ROS

2.1 Introduction
2.2 Results
2.2.1 Localization of ROS accumulation in S. asiatica seedlings.
2.2.3 ROS accumulation is not due to wounding
2.2.4 ROS accumulate in extracellular spaces
2.2.5 Regulation of ROS accumulation
2.2.6 Fluorescence loss is due to change in ROS production
2.2.7 H2O2 regulation correlates with haustorial induction
2.2.8 ROS regulation is robust
2.2.9 ROS production remains down regulated upon haustorium commitment
2.3 Discussion

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