Department of Molecular Biology, Sejong University, Seoul, 143-747, Republic of Korea.
Department of Bioindustry and Bioresource Engineering, Sejong University, Seoul, 143-747, Republic of Korea.
Plant Mol Biol. 2021 Jan;105(1-2):115-132. doi: 10.1007/s11103-020-01072-1. Epub 2020 Sep 14.
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 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 (HO and O) 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.
CAX3 编码的阳离子/质子交换体的过表达通过提高 Ca 水平来激活抗氧化酶，从而降低 ROS（活性氧），增强 Cd 耐受性 CAXs（阳离子/质子交换体）参与将 Mn、Li 和 Cd 等阳离子以及 Ca 从细胞质隔离到液泡中，利用质子梯度。此外，已经报道 CAX1、2 和 4 参与 Cd 耐受性。有趣的是，已经报道 CAX3 的表达在表达 Hb1（血红蛋白 1）或 UBC1（Ub 连接酶 1）的 Cd 耐受转基因植物中被 Cd 增强。因此，为了研究 CAX3 是否在增加 Cd 耐受性中起作用，在拟南芥中过表达了拟南芥和烟草的 CAX3。与对照植物相比，两种转基因植物都表现出 Cd 耐受性增加，Cd 积累没有变化，Ca 水平升高。支持这些结果的是，AtCAX3-拟南芥显示 Cd 转运体的表达没有变化，但 Ca 外排体的表达降低，Ca 外排率降低。相比之下，atcax3 敲除拟南芥表现出 Cd 耐受性降低，而 Cd 水平没有改变。Δ90-AtCAX3（自动抑制结构域缺失）的表达增加了酵母中的 Cd 和 Ca 耐受性，而 AtCAX3 的表达没有增加。有趣的是，在 CAX3 表达的转基因植物中观察到 ROS（HO 和 O）的积累减少，同时抗氧化酶活性（SOD、CAT、GR）更高。总之，CAX3 的过表达可能通过激活抗氧化酶来降低 Cd 诱导的 ROS 产生，从而增强 Cd 耐受性，并通过干预 ROS 产生和 Cd 诱导的细胞质 Ca 峰之间的正反馈回路来增强 Cd 耐受性。
