Detection and Adaptation in Parasitic Angiosperm Host Selection

David G Lynn,Lizhi Liang,Jenil Jariwala,Andrew G Palmer,Yue Liu

doi:10.4236/ajps.2016.78123

Abstract

Developmental transitions in some parasitic angiosperms are tied directly to host-derived chemical cues (xenognosins). The obligate hemi-parasite Striga asiatica, initiates the root apical meristem population (germination), development of the host attachment organ (the haustorium), and shoot apical meristem initiation (seed coat shedding) in response to specific xengonosins. These checkpoints synchronize spatial and temporal tissue development. We have now exploited the external control over these developmental transitions to trace functional expression in haustorial organogenesis. Genes associated with phytohormone regulation, metabolism, vascular tissue development, and reactive oxygen species (ROS) production identified in this study suggest an elaborate and global response closely tied to plant defense and redox chemistry that may also be components of a more general quorum sensing-type mechanism in plants.

Highlights

While many adaptive or learned strategies have been acquired through biological evolution, nowhere are the learning processes more acute or dynamic than at mutualistic interfaces [1]
We began by considering exposure times and conditions for each of the xenognosin-mediated developmental transitions: root apical meristem initiation, haustorial organogenesis, and shoot apical meristem (SAM) initiation
The arrested dormancy of the shoot apical meristem was observed by the shedding of the seed coat, which we used as a simple reporter

Summary

Introduction

While many adaptive or learned strategies have been acquired through biological evolution, nowhere are the learning processes more acute or dynamic than at mutualistic interfaces [1]. Distinct classes of xenognosins provide the necessary and sufficient stimulus to initiate at least three separate developmental transitions, each of which is crucial to the successful development of the parasite [3]-[5] (Figure 1). Reactive oxygen species (ROS) are actively exuded at the parasite root tip such that contact with host cell walls oxidatively liberates p-benzoquinone (pBQ) products. These pBQs are necessary and sufficient to initiate haustorial development; arrest of vegetative growth, induction of radial swelling of the root tip, and initiation of the ectopic root (haustorial) hairs (Figure 1(b)). Endogenous hormones derived by tapping the host vascular system [12] may allow the plant to complete its lifecycle, transitioning back to vegetative growth to reach seed set and, senescence (Figure 1(d) & Figure 1(e))

Methods

Results

Conclusion