Fourcroy Pierre, Vansuyt Gérard, Kushnir Sergei, Inzé Dirk, Briat Jean-François
Biochimie et Physiologie Moléculaire des Plantes, Université Montpellier 2, Institut National de la Recherche Agronomique et Ecole Nationale Supérieure Agronomique, Montpellier, France.
Plant Physiol. 2004 Feb;134(2):605-13. doi: 10.1104/pp.103.029876. Epub 2004 Jan 22.
Iron (Fe) is an essential element for living organisms. However, under aerobic conditions, its use is complicated because of its high insolubility and its potential toxicity through reactivity with reduced forms of oxygen. In plants, Fe overload can lead to intracellular concentrations beyond the storage and detoxification capacities of cells. Such a displacement toward a pro-oxidant state can activate antioxidant defenses, including Fe-mediated expression of ascorbate peroxidase genes. In this work, we demonstrate that Fe overload specifically induces the AtAPX1 gene encoding a cytosolic ascorbate peroxidase in Arabidopsis leaves. The strong constitutive expression of the AtAPX1 gene in roots is unaffected by Fe and depends on the first 5'-untranslated region intron. Presence of an AtAPX1 expressed sequence tag in the Arabidopsis database, longer in its 5' region than what could be predicted from the published AtAPX1transcription initiation site, leads to define a new transcription initiation region for this gene. A minimal promoter sequence enabling Fe-induced expression of the AtAPX1 gene is defined by following expression of various AtAPX1::beta-glucuronidase constructs in transformed Arabidopsis plantlets. This 118-bp minimal promoter sequence contains an Fe-dependent regulatory sequence-like cis-element known to be necessary for maize (Zea mays) and Arabidopsis ferritin gene derepression in response to Fe overload. Site-directed mutagenesis of this element within the AtAPX1 promoter sequence does not abolish the Fe-dependent activation of a reporter gene, indicating that it is likely not involved in the Fe-regulated expression of the AtAPX1 gene.
铁（Fe）是生物体必需的元素。然而，在有氧条件下，由于其高度不溶性以及与还原态氧反应产生潜在毒性，铁的利用变得复杂。在植物中，铁过载会导致细胞内铁浓度超出细胞的储存和解毒能力。这种向促氧化状态的转变可以激活抗氧化防御机制，包括铁介导的抗坏血酸过氧化物酶基因的表达。在这项研究中，我们证明铁过载特异性地诱导拟南芥叶片中编码胞质抗坏血酸过氧化物酶的AtAPX1基因。AtAPX1基因在根中的强组成型表达不受铁的影响，并且依赖于第一个5'非翻译区内含子。拟南芥数据库中存在一个AtAPX1表达序列标签，其5'区域比根据已发表的AtAPX1转录起始位点预测的更长，这导致确定了该基因的一个新的转录起始区域。通过在转化的拟南芥幼苗中检测各种AtAPX1::β-葡萄糖醛酸酶构建体的表达，确定了一个能够使AtAPX1基因受铁诱导表达的最小启动子序列。这个118 bp的最小启动子序列包含一个铁依赖性调控序列样顺式元件，已知该元件对于玉米（Zea mays）和拟南芥铁蛋白基因在铁过载时的去抑制是必需的。对AtAPX1启动子序列中的这个元件进行定点诱变并没有消除报告基因的铁依赖性激活，这表明它可能不参与AtAPX1基因的铁调控表达。
