Key message

Over-expression of CAX3 encoding a cation/proton exchanger enhances Cd tolerance by decreasing ROS (Reactive Oxygen Species) through activating anti-oxidative enzymes via elevation of Ca level in Arabidopsis

Abstract

CAXs (cation/proton exchangers) are involved in the sequestration of cations such as Mn, Li, and Cd, as well as Ca, from cytosol into the vacuole using proton gradients. In addition, it has been reported that CAX1, 2 and 4 are involved in Cd tolerance. Interestingly, it has been reported that CAX3 expressions were enhanced by Cd in Cd-tolerant transgenic plants expressing Hb1 (hemoglobin 1) or UBC1 (Ub-conjugating enzyme 1). Therefore, to investigate whether CAX3 plays a role in increasing Cd tolerance, CAX3 of Arabidopsis and tobacco were over-expressed in Arabidopsis thaliana. Compared to control plants, both transgenic plants displayed an increase in Cd tolerance, no change in Cd accumulation, and enhanced Ca levels. In support of these, AtCAX3-Arabidopsis showed no change in expressions of Cd transporters, but reduced expressions of Ca exporters and lower rate of Ca efflux. By contrast, atcax3 knockout Arabidopsis exhibited a reduced Cd tolerance, while the Cd level was not altered. The expression of Δ90-AtCAX3 (deletion of autoinhibitory domain) increased Cd and Ca tolerance in yeast, while AtCAX3 expression did not. Interestingly, less accumulation of ROS (H₂O₂ and O₂⁻) was observed in CAX3-expressing transgenic plants and was accompanied with higher antioxidant enzyme activities (SOD, CAT, GR). Taken together, CAX3 over-expression may enhance Cd tolerance by decreasing Cd-induced ROS production by activating antioxidant enzymes and by intervening the positive feedback circuit between ROS generation and Cd-induced spikes of cytoplasmic Ca.

中文翻译：

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在拟南芥中，CAX3（阳离子/质子交换器）通过提高 Ca 浓度来降低 ROS，从而介导 Cd 耐受性。

 关键信息

拟南芥中编码阳离子/质子交换剂的CAX3的过表达通过提高 Ca 水平激活抗氧化酶来减少 ROS（活性氧），从而增强镉耐受性

 抽象的

CAX（阳离子/质子交换器）参与使用质子梯度将 Mn、Li 和 Cd 等阳离子以及 Ca 从细胞质隔离到液泡中。此外，据报道CAX1、2和4参与Cd耐受。有趣的是，据报道，在表达Hb1 （血红蛋白 1）或UBC1 （Ub 结合酶 1）的耐镉转基因植物中，Cd 增强了CAX3的表达。因此，为了研究CAX3是否在增加Cd耐受性中发挥作用，拟南芥和烟草的CAX3在拟南芥中过表达。与对照植物相比，两种转基因植物都表现出镉耐受性的增加，镉积累没有变化，并且钙水平提高。为了支持这些观点， AtCAX3-拟南芥显示 Cd 转运蛋白的表达没有变化，但 Ca 输出蛋白的表达减少，并且 Ca 流出率降低。相比之下， atcax3敲除拟南芥表现出镉耐受性降低，而镉水平没有改变。 Δ90- AtCAX3的表达（自抑制结构域的删除）增加了酵母中的 Cd 和 Ca 耐受性，而AtCAX3 的表达却没有。有趣的是，在表达CAX3的转基因植物中观察到ROS（H ₂ O ₂和O ₂ ^- ）积累较少，并且伴随着较高的抗氧化酶活性（SOD、CAT、GR）。 综上所述， CAX3过表达可能通过激活抗氧化酶减少 Cd 诱导的 ROS 产生以及干预 ROS 产生和 Cd 诱导的细胞质 Ca 尖峰之间的正反馈回路来增强 Cd 耐受性。