POSTECH-UZH Global Research Laboratory, Division of Integrative Biology and Biotechnology, Pohang University of Science and Technology, Pohang, 790-784, Korea.
Plant Cell. 2009 Dec;21(12):4031-43. doi: 10.1105/tpc.109.066902. Epub 2009 Dec 22.
Cadmium (Cd) is a widespread soil pollutant; thus, the underlying molecular controls of plant Cd tolerance are of substantial interest. A screen for wheat (Triticum aestivum) genes that confer Cd tolerance to a Cd hypersensitive yeast strain identified Heat shock transcription factor A4a (HsfA4a). Ta HsfA4a is most similar to the class A4 Hsfs from monocots. The most closely related rice (Oryza sativa) homolog, Os HsfA4a, conferred Cd tolerance in yeast, as did Ta HsfA4a, but the second most closely related rice homolog, Os HsfA4d, did not. Cd tolerance was enhanced in rice plants expressing Ta HsfA4a and decreased in rice plants with knocked-down expression of Os HsfA4a. An analysis of the functional domain using chimeric proteins constructed from Ta HsfA4a and Os HsfA4d revealed that the DNA binding domain (DBD) of HsfA4a is critical for Cd tolerance, and within the DBD, Ala-31 and Leu-42 are important for Cd tolerance. Moreover, Ta HsfA4a-mediated Cd resistance in yeast requires metallothionein (MT). In the roots of wheat and rice, Cd stress caused increases in HsfA4a expression, together the MT genes. Our findings thus suggest that HsfA4a of wheat and rice confers Cd tolerance by upregulating MT gene expression in planta.
镉（Cd）是一种广泛存在的土壤污染物，因此，植物耐镉的潜在分子调控机制引起了广泛关注。在筛选能够赋予小麦（Triticum aestivum）耐镉性的基因时，我们发现了热休克转录因子 A4a（HsfA4a）。Ta HsfA4a 与单子叶植物的 A4 类 Hsfs 最为相似。与 Ta HsfA4a 最接近的水稻（Oryza sativa）同源物 Os HsfA4a，能够在酵母中赋予其耐镉性，而第二接近的同源物 Os HsfA4d 则不能。在表达 Ta HsfA4a 的水稻植株中，Cd 耐受性增强，而在 Os HsfA4a 表达下调的水稻植株中，Cd 耐受性降低。通过构建 Ta HsfA4a 和 Os HsfA4d 的嵌合蛋白对功能域进行分析，发现 HsfA4a 的 DNA 结合域（DBD）对于 Cd 耐受性至关重要，并且在 DBD 中，Ala-31 和 Leu-42 对于 Cd 耐受性非常重要。此外，Ta HsfA4a 介导的酵母 Cd 抗性需要金属硫蛋白（MT）。在小麦和水稻的根中，Cd 胁迫导致 HsfA4a 表达增加，同时 MT 基因也增加。因此，我们的研究结果表明，小麦和水稻的 HsfA4a 通过在植物体内上调 MT 基因的表达来赋予 Cd 耐受性。
