Role of Cation/Proton Exchangers in Abiotic Stress Signaling and Stress Tolerance in Plants

The generation of cytosolic Ca2+ signals is an early response in plants to many environmental stresses. Ca2+ transporters play a critical role in the generation of these signals and the maintenance of cellular Ca2+ homeostasis. A major class of Ca2+ transporter is the Ca2+/H+ exchanger (CAX), which is almost ubiquitous throughout every domain of life but has been best characterised in higher plants. CAX transporters of Arabidopsis thaliana have been particularly well studied and have been shown to have diverse roles in vacuolar sequestration of Ca2+ and other cations, which provide an important mechanism for ion tolerance. Recent genetic studies of CAX transporters from various plant species indicate that these proteins may also play a role in the response to specific abiotic stresses. Altered sensitivity of CAX mutant plants to abiotic stresses such as salt stress and cold stress has been observed. The potential role of CAX-type cation transporters in environmental stress response is reviewed here. In particular, we discuss whether these high-capacity, low-affinity Ca2+ transporters play a central role in modulating Ca2+ signals in response to abiotic stresses.