CAX3 (cation/proton exchanger) mediates a Cd tolerance by decreasing ROS through Ca elevation inArabidopsis

Key message Over-expression ofCAX3encoding 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 thatCAX1,2and4are involved in Cd tolerance. Interestingly, it has been reported thatCAX3expressions were enhanced by Cd in Cd-tolerant transgenic plants expressingHb1(hemoglobin 1) orUBC1(Ub-conjugating enzyme 1). Therefore, to investigate whetherCAX3plays a role in increasing Cd tolerance,CAX3of Arabidopsis and tobacco were over-expressed inArabidopsis 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,atcax3knockout Arabidopsis exhibited a reduced Cd tolerance, while the Cd level was not altered. The expression of Delta 90-AtCAX3(deletion of autoinhibitory domain) increased Cd and Ca tolerance in yeast, whileAtCAX3expression did not. Interestingly, less accumulation of ROS (H(2)O(2)and O-2(-)) was observed inCAX3-expressing transgenic plants and was accompanied with higher antioxidant enzyme activities (SOD, CAT, GR). Taken together,CAX3over-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.

Automated summary

Over-expression of the CAX3 gene enhances Cd tolerance in Arabidopsis by decreasing ROS levels, activating antioxidant enzymes, and regulating cytoplasmic Ca spikes.