Poster: Root Biology

Abs # 518: Allelopathy and exotic plant invasion: from molecules and genes to communities.

Presenter:	Bais, Harsh Pal, hpbais@yahoo.com
Authors	Bais, Harsh Pal (A)   Vepachedu, Ramarao  (A)   Gilroy, Simon  (B)   Callaway, Ragan  (C)   Vivanco, Jorge M (A)
Affiliations:	(A): Department of Horticulture, Cell and Molecular Biology Graduate Program, Colorado State University, Fort Collins, CO-80523-1173 (B): Department of Biology, Pennsylvania State University, University Park, PA 16802 (C): Division of Biological Sciences, University of Montana, Missoula, MO 59812

Many of the world’s most common and ecologically devastating exotic invaders competitively eliminate neighbors in invaded communities but coexist with neighbors in their native habitat. Here we present evidence that Centaurea maculosa (spotted knapweed), an invasive species in the Western U.S., displaces native plant species by exuding a phytotoxic chemical from its roots, and we provide a detailed discussion of the ecological, physiological, cellular, biochemical, and genomic mechanisms by which this type of allelopathy operates. Our results overall support a “novel weapons” hypothesis for invasive success. We identify (-)-catechin, a root secreted allelochemical, as a major factor in C. maculosa’s overwhelming competitive dominance in many North American plant communities. Our results show inhibition of native species’ growth and germination in field soils at natural concentrations of the allelochemical. This effect is due to (-)-catechin’s cell-specific targeting of meristmatic and elongation zone cells in the roots of susceptible plants. Cell-specific targeting is evidenced by cytoplasmic condensation followed by a cascade of cell death proceeding backwards up through the root stele. In Arabidopsis thaliana, the allelochemical triggers a rapid cascade of stress responses such as the induction of a wave of reactive oxygen species (ROS) initiated at the root apex, which leads to a Ca²⁺ signaling cascade triggering a cellular pH decrease, and allelochemical-induced genome-wide changes in gene expression patterns. These responses kill cells in the root meristem and elongation zone and ultimately lead to the death of the entire root system of susceptible species.