Courbot Mikael, Willems Glenda, Motte Patrick, Arvidsson Samuel, Roosens Nancy, Saumitou-Laprade Pierre, Verbruggen Nathalie
Laboratoire de Physiologie et de Génétique moléculaire des Plantes, Université Libre de Bruxelles, B-1050 Brussels, Belgium.
Plant Physiol. 2007 Jun;144(2):1052-65. doi: 10.1104/pp.106.095133. Epub 2007 Apr 13.
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.
镉（Cd）耐受性似乎是拟南芥琴叶拟南芥亚种的一种组成型物种水平性状。因此，在琴叶拟南芥与其最接近的非耐受可育近缘种岩生拟南芥之间进行了种间杂交，并利用第一代回交群体（BC1）来定位镉耐受性的数量性状位点（QTL）。鉴定出了三个QTL，它们解释了定位群体中43%、24%和16%的表型变异。重金属转运ATP酶4（HMA4）编码一种预测的重金属ATP酶，与主要QTL Cdtol-1的峰值共定位，因此对其进行了进一步研究。琴叶拟南芥根和地上部分中HMA4转录本水平高于岩生拟南芥。此外，在QTL Cdtol-1处携带HMA4琴叶拟南芥等位基因的所有BC1基因型中，HMA4也有更高的表达，这与另外两个QTL处琴叶拟南芥等位基因的存在无关。在酵母（酿酒酵母）中过表达AhHMA4，通过降低酵母细胞中的镉和锌含量，支持了HMA4在锌（Zn）和镉转运中的作用。在表皮烟草（烟草）细胞中，AhHMA4:绿色荧光蛋白明显定位于质膜。综上所述，所有现有数据表明，HMA4 P(1B)型ATP酶的表达升高是植物在镉/锌过量条件下通过维持细胞质中低细胞镉（Cd2+）和锌（Zn2+）浓度来提高镉/锌耐受性的一种有效机制。
