College of Environmental and Resource Sciences, Zhejiang University, Hanzhou, China.
PLoS One. 2012;7(6):e38535. doi: 10.1371/journal.pone.0038535. Epub 2012 Jun 22.
Thlaspi caerulescens is a natural selected heavy metal hyperaccumulator that can not only tolerate but also accumulate extremely high levels of heavy metals in the shoots. Thus, to identify the transportors involved in metal long-distance transportation is very important for understanding the mechanism of heavy metal accumulation in this hyperaccumulator.
METHODOLOGY/PRINCIPAL FINDINGS: We cloned and characterized a novel gene TcOPT3 of OPT family from T. caerulescens. TcOPT3 was pronouncedly expressed in aerial parts, including stem and leaf. Moreover, in situ hybridization analyses showed that TcOPT3 expressed in the plant vascular systems, especially in the pericycle cells that may be involved in the long-distance transportation. The expression of TcOPT3 was highly induced by iron (Fe) and zinc (Zn) deficiency, especially in the stem and leaf. Sub-cellular localization showed that TcOPT3 was a plasma membrane-localized protein. Furthermore, heterogonous expression of TcOPT3 by mutant yeast (Saccharomyces cerevisiae) complementation experiments demonstrated that TcOPT3 could transport Fe(2+) and Zn(2+). Moreover, expression of TcOPT3 in yeast increased metal (Fe, Zn, Cu and Cd) accumulation and resulted in an increased sensitivity to cadmium (Cd) and copper (Cu).
Our data demonstrated that TcOPT3 might encode an Fe/Zn/Cd/Cu influx transporter with broad-substrate. This is the first report showing that TcOPT3 may be involved in metal long-distance transportation and contribute to the heavy metal hyperaccumulation.
天蓝遏蓝菜是一种天然选择的重金属超积累植物，它不仅能耐受而且能在地上部分（包括茎和叶）积累极高水平的重金属。因此，鉴定参与金属长距离运输的转运体对于理解该超积累植物中重金属积累的机制非常重要。
方法/主要发现：我们从天蓝遏蓝菜中克隆并鉴定了 OPT 家族的一个新基因 TcOPT3。TcOPT3 在地上部分（包括茎和叶）中表达明显。此外，原位杂交分析表明 TcOPT3 在植物的维管系统中表达，特别是在可能参与长距离运输的周皮细胞中表达。TcOPT3 的表达受铁（Fe）和锌（Zn）缺乏的高度诱导，特别是在茎和叶中。亚细胞定位表明 TcOPT3 是一种质膜定位蛋白。此外，通过突变酵母（酿酒酵母）的异源表达互补实验表明，TcOPT3 可以转运 Fe（2+）和 Zn（2+）。此外，在酵母中表达 TcOPT3 增加了金属（Fe、Zn、Cu 和 Cd）的积累，并导致对镉（Cd）和铜（Cu）的敏感性增加。
我们的数据表明，TcOPT3 可能编码一种 Fe/Zn/Cd/Cu 输入转运体，具有广泛的底物特异性。这是第一个表明 TcOPT3 可能参与金属长距离运输并有助于重金属超积累的报告。
