Transcriptome responses to aluminum stress in roots of aspen (Populus tremula)
1 Swiss Federal Institute for Forest, Snow and Landscape Research (WSL), Zürcherstrasse 111, CH-8903 Birmensdorf, Switzerland
2 Functional Genomics Center Zurich, University of Zurich and Swiss Federal Institute of Technology Zurich, Winterthurerstrasse 190, CH-8057 Zurich, Switzerland
3 Institute of Chemistry and Biological Chemistry, Zurich University of Applied Sciences, School of Life Sciences and Facility Management, Einsiedlerstrasse 31, CH-8820 Wädenswil, Switzerland
4 Institute of Bioinformatics and System Biology, Helmholtz Center Munich, Ingolstädter Landstraße 1, D-85764 Neuherberg, Germany
5 Department of Biology, University of Fribourg, Chemin du Musée 10, CH-1700 Fribourg, Switzerland
6 Genetic Diversity Centre, Swiss Federal Institute of Technology, Universitätstrasse 16, CH-8092 Zurich, Switzerland
7 Dualsystems Biotech AG, Grabenstrasse 11a, CH-8952 Schlieren, Switzerland
8 Philip Morris International Research & Development, Philip Morris Products SA, Quai Jeanrenaud 56, CH-2000 Neuchâtel, Switzerland
BMC Plant Biology 2010, 10:185 doi:10.1186/1471-2229-10-185Published: 23 August 2010
Ionic aluminum (mainly Al3+) is rhizotoxic and can be present in acid soils at concentrations high enough to inhibit root growth. Many forest tree species grow naturally in acid soils and often tolerate high concentrations of Al. Previously, we have shown that aspen (Populus tremula) releases citrate and oxalate from roots in response to Al exposure. To obtain further insights into the root responses of aspen to Al, we investigated root gene expression at Al conditions that inhibit root growth.
Treatment of the aspen roots with 500 μM Al induced a strong inhibition of root growth within 6 h of exposure time. The root growth subsequently recovered, reaching growth rates comparable to that of control plants. Changes in gene expression were determined after 6 h, 2 d, and 10 d of Al exposure. Replicated transcriptome analyses using the Affymetrix poplar genome array revealed a total of 175 significantly up-regulated and 69 down-regulated genes, of which 70% could be annotated based on Arabidopsis genome resources. Between 6 h and 2 d, the number of responsive genes strongly decreased from 202 to 26, and then the number of changes remained low. The responses after 6 h were characterized by genes involved in cell wall modification, ion transport, and oxidative stress. Two genes with prolonged induction were closely related to the Arabidopsis Al tolerance genes ALS3 (for Al sensitive 3) and MATE (for multidrug and toxin efflux protein, mediating citrate efflux). Patterns of expression in different plant organs and in response to Al indicated that the two aspen genes are homologs of the Arabidopsis ALS3 and MATE.
Exposure of aspen roots to Al results in a rapid inhibition of root growth and a large change in root gene expression. The subsequent root growth recovery and the concomitant reduction in the number of responsive genes presumably reflect the success of the roots in activating Al tolerance mechanisms. The aspen genes ALS3 and MATE may be important components of these mechanisms.