Allelopathy and exotic plant invasion: from molecules and genes to species interactions.

Here we present evidence that Centaurea maculosa (spotted knapweed), an invasive species in the western United States, displaces native plant species by exuding the phytotoxin (-)-catechin from its roots. Our results show inhibition of native species' growth and germination in field soils at natural concentrations of (-)-catechin. In susceptible species such as Arabidopsis thaliana, the allelochemical triggers a wave of reactive oxygen species (ROS) initiated at the root meristem, which leads to a Ca2+ signaling cascade triggering genome-wide changes in gene expression and, ultimately, death of the root system. Our results support a "novel weapons hypothesis" for invasive success.