Abstract
Metal tolerance is often a result of metal storage or distribution. Thus, with the goal of advancing the molecular understanding of such metal homeostatic mechanisms, natural variation of metal tolerance in Arabidopsis thaliana was investigated. Substantial variation exists in tolerance of excess copper (Cu), zinc (Zn) and cadmium (Cd). Two accessions, Col-0 and Bur-0, and a recombinant inbred line (RIL) population derived from these parents were chosen for further analysis of Cd and Zn tolerance variation, which is evident at different plant ages in various experimental systems and appears to be genetically linked. Three QTLs, explaining in total nearly 50% of the variation in Cd tolerance, were mapped. The one obvious candidate gene in the mapped intervals, HMA3, is unlikely to contribute to the variation. In order to identify additional candidate genes the Cd responses of Col-0 and Bur-0 were compared at the transcriptome level. The sustained common Cd response of the two accessions was dominated by processes implicated in plant pathogen defense. Accession-specific differences suggested a more efficient activation of acclimative responses as underlying the higher Cd tolerance of Bur-0. The second hypothesis derived from the physiological characterization of the accessions is a reduced Cd accumulation in Bur-0.
Highlights
Plant traits show enormous intraspecific natural variation
We detected variation in Cd tolerance ranging from 31 ± 5 to 60 ± 12% Relative root growth (RRG) in the presence of Cd
Huge variation was detected in Cu tolerance because of the extreme Cu-sensitivity of Cvi-0 (7.5 ± 3.4%) (Supplementary Fig. S1) which is attributable to a loss of HMA5 function[16]
Summary
Plant traits show enormous intraspecific natural variation. Molecular dissection of this variation can lead to new mechanistic insights into physiological or developmental processes and ideally yield an understanding of local adaptation to specific habitats. The natural variation in many different traits has already been studied in A. thaliana, enabling major progress in the understanding of diverse biological phenomena such as control of flowering time or herbivore defense[3]. A homeostatic system comprising metal transporters, metal ligands and regulatory proteins maintains the concentrations of essential elements within rather narrow physiological ranges inside plant tissues and limits the accumulation of non-physiological elements[7, 8]. Many genes contributing to metal tolerance are part of the homeostatic network controlling metal accumulation and distribution. Variation in the recently identified arsenate (AsV) reductase ATQ1/HAC1 controls both differences in arsenate tolerance[19] and the shoot accumulation of As20
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