Minisymposium 11: Secondary Metabolites

Abs # 23004: Unraveling the hidden potential of root exudates: from allelochemicals to antibiotics

Presenter:	Vivanco, Jorge M, jvivanco@lamar.colostate.edu
Authors	Vivanco, Jorge M (A) (B)  Bais, Harsh P (A)
Affiliations:	(A): Colorado State University - Department of Horticulture (B): Colorado State University - Cell and Molecular Biology Graduate Program, and Graduate Degree Program in Ecology
Web Site:	http://lamar.colostate.edu/~jvivanco/

Our understanding of the biology, biochemistry and genetic development of roots has considerably improved during the last decade. In contrast, our knowledge of the processes mediated by roots, such as the secretion of root exudates, is incomplete at best. My laboratory is working to fill these gaps. We know that through the exudation of a wide variety of secondary metabolites, roots may regulate the soil microbial community in their immediate vicinity, cope with herbivores, encourage beneficial symbioses, change the chemical and physical properties of the soil, and inhibit the growth of competing plant species. As an example of the latter, we will present conclusive 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 will discuss some mechanisms by which this type of allelopathy operates. We have identified (-)-catechin, a root secreted allelochemical, as a major factor in C. maculosa's overwhelming competitive dominance in many North American plant communities. Although C. maculosa roots exude (±)-catechin, only the (-)-catechin enantiomer was phytotoxic. (+)-Catechin had antibacterial activity against root infesting pathogens, which (-)-catechin did not show. Our results show inhibition of native species' growth and germination in field soils at natural concentrations of the allelochemical. In Arabidopsis thaliana, (-)-catechin triggers a rapid cascade of stress responses such as the induction of a wave of reactive oxygen species (ROS) at the root apex, leading to a Ca2+ signaling cascade, a decrease in cellular pH, and finally 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. We will also describe our work on the characterization of rosmarinic acid (RA), a potent root-secreted antimicrobial agent showing activity against a wide range of soil-borne plant pathogens. Finally, we will show our preliminary profiling of the secondary metabolites of Arabidopsis thaliana root exudates. This research may open new vistas for the characterization of new bioactive compounds and the discovery of new genes and their functions. Our presentation will show the untapped potential of root exudates as a general system for isolating biologically-active secondary metabolites.