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First published online September 22, 2006; 10.1104/pp.106.082073 Plant Physiology 142:1127-1147 (2006) © 2006 American Society of Plant Biologists Large Expression Differences in Genes for Iron and Zinc Homeostasis, Stress Response, and Lignin Biosynthesis Distinguish Roots of Arabidopsis thaliana and the Related Metal Hyperaccumulator Thlaspi caerulescens1,[W]Laboratory of Genetics, Wageningen University, 6703 BD Wageningen, The Netherlands (J.E.v.d.M., L.A.V., M.K., M.G.M.A.); Institute of Ecological Sciences, Faculty of Earth and Life Sciences, Vrije Universiteit, 1081 HV Amsterdam, The Netherlands (H.S.); ServiceXS BV, 2333 AL Leiden, The Netherlands (J.K.); Agilent Technologies, Little Falls Site, Wilmington, Delaware 19808–1644 (S.C.); and Bioinformatics Laboratory, Department of Clinical Epidemiology, Biostatistics and Bioinformatics, Academic Medical Center, University of Amsterdam, 1100 DD Amsterdam, The Netherlands (P.D.M., E.V.L.v.T.)
The micronutrient zinc has an essential role in physiological and metabolic processes in plants as a cofactor or structural element in 300 catalytic and noncatalytic proteins, but it is very toxic when available in elevated amounts. Plants tightly regulate their internal zinc concentrations in a process called zinc homeostasis. The exceptional zinc hyperaccumulator species Thlaspi caerulescens can accumulate up to 3% of zinc, but also high amounts of nickel and cadmium, without any sign of toxicity. This should have drastic effects on the zinc homeostasis mechanism. We examined in detail the transcription profiles of roots of Arabidopsis thaliana and T. caerulescens plants grown under deficient, sufficient, and excess supply of zinc. A total of 608 zinc-responsive genes with at least a 3-fold difference in expression level were detected in A. thaliana and 352 in T. caerulescens in response to changes in zinc supply. Only 14% of these genes were also zinc responsive in A. thaliana. When comparing A. thaliana with T. caerulescens at each zinc exposure, more than 2,200 genes were significantly differentially expressed (
1 This work was supported by the NWO (Programma Genomics grant no. 050–10–166 to J.E.v.d.M.), the European Union PHYTAC project (QLRT–2001–00429), and the European Union RTN-Metalhome project (HPRN–CT–2002–00243; H.S. and M.G.M.A.). The author responsible for distribution of materials integral to the findings presented in this article in accordance with the policy described in the Instructions for Authors (www.plantphysiol.org) is: Mark G.M. Aarts (mark.aarts{at}wur.nl). [W] The online version of this article contains Web-only data. www.plantphysiol.org/cgi/doi/10.1104/pp.106.082073 * Corresponding author; e-mail mark.aarts{at}wur.nl; fax 31–317–483146. Received April 17, 2006; accepted September 8, 2006; published September 22, 2006. This article has been cited by other articles:
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5-fold and false discovery rate < 0.05). While a large fraction of these genes are of yet unknown function, many genes with a different expression between A. thaliana and T. caerulescens appear to function in metal homeostasis, in abiotic stress response, and in lignin biosynthesis. The high expression of lignin biosynthesis genes corresponds to the deposition of lignin in the endodermis, of which there are two layers in T. caerulescens roots and only one in A. thaliana. 
