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ABSTRACT: There is huge variability among populations of the hyperaccumulator Noccaea caerulescens (formerly Thlaspi caerulescens) in their capacity to tolerate and accumulate cadmium. To gain new insights into the mechanisms underlying this variability, we estimated cadmium fluxes and further characterized the N. caerulescens heavy metal ATPase 4 (NcHMA4) gene in three populations (two calamine, Saint-Félix-de-Pallières, France and Prayon, Belgium; one serpentine, Puente Basadre, Spain) presenting contrasting levels of tolerance and accumulation. Cadmium uptake and translocation varied among populations in the same way as accumulation; the population with the highest cadmium concentration in shoots (Saint Félix-de-Pallières) presented the highest capacity for uptake and translocation. We demonstrated that the four NcHMA4 copies identified in a previous study are not fixed at the species level, and that the copy truncated in the C-terminal part encodes a functional protein. NcHMA4 expression and gene copy number was lower in the serpentine population, which was the least efficient in cadmium translocation compared to the calamine populations. NcHMA4 expression was associated with the vascular tissue in all organs, with a maximum at the crown. Overall, our results indicate that differences in cadmium translocation ability of the studied populations appear to be controlled, at least partially, by NcHMA4, while the overexpression of NcHMA4 in the two calamine populations may result from convergent evolution.
Journal of Experimental Botany 05/2012; 63(11):4179-89. · 5.36 Impact Factor
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ABSTRACT: Gene duplication is a major mechanism facilitating adaptation to changing environments. From recent genomic analyses, the acquisition of zinc hypertolerance and hyperaccumulation characters discriminating Arabidopsis halleri from its zinc sensitive/non-accumulator closest relatives Arabidopsis lyrata and Arabidopsis thaliana was proposed to rely on duplication of genes controlling zinc transport or zinc tolerance. Metal Tolerance Protein 1 (MTP1) is one of these genes. It encodes a Zn(2+)/H(+) antiporter involved in cytoplasmic zinc detoxification and thus in zinc tolerance. MTP1 was proposed to be triplicated in A. halleri, while it is present in single copy in A. thaliana and A. lyrata. Two of the three AhMTP1 paralogues were shown to co-segregate with zinc tolerance in a BC1 progeny from a cross between A. halleri and A. lyrata. In this work, the MTP1 family was characterized at both the genomic and functional levels in A. halleri. Five MTP1 paralogues were found to be present in A. halleri, AhMTP1-A1, -A2, -B, -C, and -D. Interestingly, one of the two newly identified AhMTP1 paralogues was not fixed at least in one A. halleri population. All MTP1s were expressed, but transcript accumulation of the paralogues co-segregating with zinc tolerance in the A. halleri X A. lyrata BC1 progeny was markedly higher than that of the other paralogues. All MTP1s displayed the ability to functionally complement a Saccharomyces cerevisiae zinc hypersensitive mutant. However, the paralogue showing the least complementation of the yeast mutant phenotype was one of the paralogues co-segregating with zinc tolerance. From our results, the hypothesis that pentaplication of MTP1 could be a major basis of the zinc tolerance character in A. halleri is strongly counter-balanced by the fact that members of the MTP1 family are likely to experience different evolutionary fates, some of which not concurring to increase zinc tolerance.
PLoS Genetics 01/2010; 6(4):e1000911. · 8.69 Impact Factor
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ABSTRACT: Recent advances in molecular biology have opened new perspectives for the study of plant adaptation, especially at the intraspecific level. Nowadays, scientists employing -omic results in multiple scientific fields can be optimistic of their chances of revealing mechanisms involved in adaptive population divergence. However, the investment required by integrative studies greatly reduces the number of experiments that can be performed. In this context, a comprehensive choice of accessions under study is crucial. We maintain this choice could be appreciably enlightened by population genetics because it helps putting adaptive population divergence in a spatial and historical context. As an example, we highlight the usefulness of knowledge about population genetic structure in the integrative study of metal tolerance in Arabidopsis halleri.
Current Opinion in Plant Biology 05/2008; 11(2):129-34. · 9.27 Impact Factor
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ABSTRACT: Metallophyte species that occur naturally on metal-enriched soils represent major biological resources for the improvement of phytoremediation, a benign and cost-effective technology that uses plants to clean up anthropogenic metal-polluted soils. Within the last decade, molecular genetic studies carried out on several model organisms (including Arabidopsis halleri) have considerably enhanced our understanding of metal tolerance and hyperaccumulation in plants, but the identification of the genes of interest for phytoremediation purposes remains a challenge. To meet this challenge, we propose to combine '-omics' with molecular ecology methods. Using A. halleri, we confronted molecular genetic results with: (i) within-species polymorphism and large-scale population differentiation for zinc tolerance; (ii) the demographical context (e.g. migration pattern) of the species for zinc tolerance evolution; (iii) the Quantitative Trait Loci (QTL) analysis of the genetic architecture for zinc tolerance; and (iv) the fine-scale dissection of identified QTL regions, to discuss more precisely the nature of the genes potentially involved in the adaptation to zinc-polluted soils.
Molecular Ecology 02/2008; 17(1):108-19. · 5.52 Impact Factor
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ABSTRACT: Cadmium (Cd) tolerance seems to be a constitutive species-level trait in Arabidopsis halleri sp. halleri. Therefore, an interspecific cross was made between A. halleri and its closest nontolerant interfertile relative, Arabidopsis lyrata sp. petraea, and a first-generation backcross population (BC1) was used to map quantitative trait loci (QTL) for Cd tolerance. Three QTL were identified, which explained 43%, 24%, and 16% of the phenotypic variation in the mapping population. Heavy metal transporting ATPases4 (HMA4), encoding a predicted heavy metal ATPase, colocalized with the peak of the major QTL Cdtol-1 and was consequently further studied. HMA4 transcripts levels were higher in the roots and the shoots of A. halleri than in A. lyrata sp. petraea. Furthermore, HMA4 was also more highly expressed in all BC1 genotypes harboring the HMA4 A. halleri allele at the QTL Cdtol-1, independently of the presence of an A. halleri allele at the two other QTL. Overexpression of AhHMA4 in yeast (Saccharomyces cerevisiae) supported a role of HMA4 in zinc (Zn) and Cd transport by reducing the Cd and Zn contents of the yeast cells. In epidermal tobacco (Nicotiana tabacum) cells, AhHMA4:green fluorescent protein was clearly localized in the plasma membrane. Taken together, all available data point to the elevated expression of HMA4 P(1B)-type ATPase as an efficient mechanism for improving Cd/Zn tolerance in plants under conditions of Cd/Zn excess by maintaining low cellular Cd(2+) and Zn(2+) concentrations in the cytoplasm.
Plant physiology 07/2007; 144(2):1052-65. · 6.53 Impact Factor
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ABSTRACT: Thlaspi caerulescens exhibits a unique capacity for cadmium tolerance and accumulation. We investigated the molecular basis of this exceptional Cd(2+) tolerance by screening for T. caerulescens genes, which alleviate Cd(2+) toxicity upon expression in Saccharomyces cerevisiae. This allowed for the isolation of a cDNA encoding a peptide with homology to the C-terminal part of a heavy metal ATPase. The corresponding TcHMA4 full-length sequence was isolated from T. caerulescens and compared to its homolog from Arabidopsis thaliana (AtHMA4). Expression of TcHMA4 and AtHMA4 cDNAs conferred Cd sensitivity in yeast, while expression of TcHMA4-C and AtHMA4-C cDNAs encoding the C-termini of, respectively, TcHMA4 and AtHMA4 conferred Cd tolerance. Moreover, heterologous expression in yeast suggested a higher Cd binding capacity of TcHMA4-C compared to AtHMA4-C. In planta, both HMA4 genes were expressed at a higher level in roots than in shoots. However, TcHMA4 shows a much higher constitutive expression than AtHMA4. Our data indicate that HMA4 could be involved in Cd(2+) transport and possibly in the Cd hyperaccumulation character.
FEBS Letters 08/2004; 569(1-3):140-8. · 3.54 Impact Factor
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ABSTRACT: The voltage-dependent anion-selective channel (VDAC) is a mitochondrial outer membrane ion channel. Different isoforms exist in plants but information about their specific role remains to be established. Our purpose is to find out the structural features common to three rice VDAC isoforms and to investigate their (post)transcriptional regulation in response to an osmotic stress. Two new cDNAs encoding mitochondrial VDAC from rice (Oryza sativa) were isolated, sequenced and characterized: a phylogenetic reconstruction permitted identification of orthologues in Poaceae and computer-based analyses predicted 18 transmembrane beta-strands, one amphipathic alpha-helix and two different phosphorylation motifs. The expression of three rice vdac genes was investigated. Northern blot analyses indicated that they were expressed in all plant tissues. There was a differential expression of osvdac1 and osvdac3, whereas osvdac2 was homogeneously expressed in all tissues. No change in vdac expression was observed under an osmotic stress. However, a fast-enhanced expression of vdac was observed in roots during the recovery period after stress release. This enhanced expression is not correlated to the amount of VDAC protein detected in roots suggesting a posttranscriptional regulation.
Biochimica et Biophysica Acta 02/2003; 1625(1):43-51. · 4.66 Impact Factor
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ABSTRACT: The voltage-dependent anion-selective channel (VDAC) is a mitochondrial outer membrane ion channel. The putative promoter of the rice vdac isoform2 (osvdac2) was isolated by screening a rice genomic library. Computer-based analyses predicted a TATA box, a putative transcription start and several transcription factor-binding sites including pollen specific elements. The promoter region was fused to the gus reporter gene and introduced into rice by Agrobacterium-mediated transformation. Histochemical and cell-type localizations indicated an overall expression of this promoter with a strong expression in actively growing lateral roots and in the pollen grains. Quantitative experiments showed that the osvdac2 promoter has a strong specific activity in both root and shoot. Thus, the osvdac2 promoter could be a good alternative to viral promoters (e.g. CaMV 35S) to overexpress genes in transgenic Poaceae.
Biochimica et Biophysica Acta 01/2003; 1579(2-3):133-41. · 4.66 Impact Factor
