Plasma membrane-associated calcium signaling regulates arsenate tolerance in Arabidopsis

Arsenate [As(V)] is a metalloid with heavy metal properties and is widespread in many environments. Dietary intake of food derived from arsenate-contaminated plants constitutes a major fraction of the potentially health-threatening human exposure to arsenic. However, the mechanisms underlying how plants respond to arsenate stress and regulate the function of relevant transporters are poorly understood. Here, we observed that As(V) stress induces a significant Ca2+ signal in Arabidopsis (Arabidopsis thaliana) roots. We then identified a calcium-dependent protein kinase, CALCIUM-DEPENDENT PROTEIN KINASE 23 (CPK23), that interacts with the plasma membrane As(V)/Pi transporter PHOSPHATE TRANSPORTER 1;1 (PHT1;1) in vitro and in vivo. cpk23 mutants displayed a sensitive phenotype under As(V) stress, while transgenic Arabidopsis plants with constitutively active CPK23 showed a tolerant phenotype. Furthermore, CPK23 phosphorylated the C-terminal domain of PHT1;1, primarily at Ser514 and Ser520. Multiple experiments on PHT1;1 variants demonstrated that PHT1;1S514 phosphorylation is essential for PHT1;1 function and localization under As(V) stress. In summary, we revealed that plasma-membrane-associated calcium signaling regulates As(V) tolerance. These results provide insight for crop bioengineering to specifically address arsenate pollution in soils.