Arabidopsis IONIC CURRENT FAMILY A proteins facilitate environmental calcium acquisition essential for stress...

Calcium (Ca²⁺) is an essential macronutrient for plant growth and defence, yet the molecular mechanisms regulating its uptake from soil remain largely undefined. Through bioinformatics and electrophysiological screening, we identified a group of plant-specific proteins, named the IONIC CURRENT FAMILY A (ICAs), which confer Ca²⁺-permeable non-selective cation channel (CNCC) activities in heterologous systems. In Arabidopsis thaliana, AtICA1, AtICA2, AtICA3 and AtICA4 are predominantly expressed in root cells, and their proteins localize to the plasma membrane. Under either limited or excessive external Ca²⁺ conditions, ica1/2/3/4 quadruple mutants display hypersensitivity or reduced sensitivity, respectively, as evidenced by altered root length. In addition, these mutants show increased sensitivity to various abiotic and biotic stresses under normal Ca²⁺ conditions. The ica mutants lack the previously characterized CNCC-mediated currents in roots that facilitate cellular Ca²⁺ uptake, resulting in lower Ca²⁺ levels compared with wild-type (WT) plants. Our findings suggest that AtICA1/2/3/4 may function as components of CNCCs, mediating Ca²⁺ uptake crucial for broad environmental stress tolerance under normal Ca²⁺ conditions. This study provides molecular insight into the mechanisms governing Ca²⁺ uptake in plant roots and expands our understanding of how plants maintain Ca²⁺ homeostasis under varying environmental conditions.