Calcium sensor proteins: regulators of the function of Na+/H+ antiporters in animal and plants.

Abstract

In animal cells, Calcineurin B Homologous Proteins (CHP) are N-myristoylated, Ca2+-binding proteins that interact to and regulate Na+/H+ exchangers (NHE), through mechanisms involving protein trafficking and stability, and the regulation of ion transport activity. We show that a similar regulatory mechanism exists in Arabidopsis: the Calcineurin B-Like protein, CBL4/SOS3, binds directly to the Na+/H+ antiporter SOS1 that is essential for the salt tolerance of Arabidopsis. The SOS3-binding domain in SOS1 showed clear structural similarities with that of CHP and NHE1 in the animal system. A SOS3 protein unable to interact with SOS1 cannot recover the salt-sensitive phenotype of the Arabidopsis sos3-1 mutant. Functional consequences of SOS3/SOS1 interaction in Arabidopsis are likely the regulation of SOS1-dependent Na+ transport and SOS1 protein stability, suggesting the conservation of this regulatory mechanism between animals and plants.