Plant cell-surface GIPC sphingolipids sense salt to trigger Ca influx.

Salinity is detrimental to plant growth, crop production and food security worldwide. Excess salt triggers increases in cytosolic Ca concentration, which activate Ca-binding proteins and upregulate the Na/H antiporter in order to remove Na. Salt-induced increases in Ca have long been thought to be involved in the detection of salt stress, but the molecular components of the sensing machinery remain unknown. Here, using Ca-imaging-based forward genetic screens, we isolated the Arabidopsis thaliana mutant monocation-induced [Ca increases 1 (moca1), and identified MOCA1 as a glucuronosyltransferase for glycosyl inositol phosphorylceramide (GIPC) sphingolipids in the plasma membrane. MOCA1 is required for salt-induced depolarization of the cell-surface potential, Ca spikes and waves, Na/H antiporter activation, and regulation of growth. Na binds to GIPCs to gate Ca influx channels. This salt-sensing mechanism might imply that plasma-membrane lipids are involved in adaption to various environmental salt levels, and could be used to improve salt resistance in crops.