Scientific Correspondence Annexins: Components of the Calcium and Reactive Oxygen Signaling Network

Despite the importance of reactive oxygen species (ROS) in plant immunity, stress signaling, and development (Mori and Schroeder, 2004; Gadjev et al., 2006), the molecular identities of Ca-permeable channels responding to ROS have not been established. Here, we propose annexins as candidate channel proteins. Elevation of cytoplasmic free calcium ([Ca2+]cyt) as a regulatory step in plant immunity, stress adaptation, and development will rely on spatiotemporal control of Ca-permeable channel activity at endomembranes and the plasma membrane (PM; McAinsh and Pittman, 2009). Higher plant genomes encode multiple potential Ca-permeable channel subunits that could contribute to celland stimulus-specific patterns of [Ca2+]cyt elevation (McAinsh and Pittman, 2009; Ward et al., 2009). Numerous factors are involved in modulating channel events, including voltage, membrane stretch, pH, phosphorylation, G proteins, amino acids, cyclic nucleotides, and ROS (Ward et al., 2009). Identifying ROS-responsive Ca-permeable channels and their encoding genes will help elucidate ROS-Ca signaling networks. Annexins could be able to form a ROS-stimulated passive Ca transport pathway. Here, we examine the evidence leading to this proposal and show that plant annexins are capable of forming a Ca-permeable conductance in an oxidized membrane simulating ROS signaling conditions.