Deciphering the Sodium Sensing Mechanisms in Glycophytes and Halophytes

Plants, including halophytes (salt-tolerant) and glycophytes (salt-sensitive), have developed diverse molecular mechanisms and morphological adaptations to survive in saline environments. The cellular components and molecular processes for salinity sensing and stress tolerance have been extensively identified in glycophytes, but not so with halophytes. Salinity sensing requires the perception of a major soil salinity contributor, that is, sodium ions (Na⁺). The exact molecular mechanism or pathway for Na⁺ perception is still unclear. The investigations into potential Na⁺ sensor candidates uncovered glycosyl inositol phosphoryl ceramide (GIPC) phospholipids with direct evidence. In cells, Na⁺ ions are also sensed by various Non-selective cation channels (NSCCs), including the cyclic nucleotide-gated channels (CNGCs) and glutamate receptors (GLRs), and other receptor-like kinases (RLKs). This review surveyed the roles of GIPCs, CNGCs, GLRs, RLKs, including the Catharanthus roseus RLK1-like kinases, leucine-rich repeat extensins, lectin RLKs, and wall-associated kinases, as potential Na⁺ sensors in glycophytes and halophytes. Based on current information on these receptors, we proposed new models of Na⁺ sensing mechanisms in both plant types. The comparison of possible Na⁺ sensing mechanisms between glycophytes and halophytes might provide future research avenues for improving salt tolerance in crops.