The slow-type anion channel PcSLAH3 from the xerophyte Pugionium cornutum is involved in Cl− transport and Cl−/Na+ homeostasis under saline condition

The succulent xerophyte Pugionium cornutum efficiently translocates chloride ions (Cl - ) absorbed by the roots to its shoots for osmotic adjustment under salt stress, a trait uncommon in most crops. However, the underlying molecular mechanisms remain further investigated. The slow-type anion channel AtSLAH3 is known to be involved in Cl - transport from roots to shoots through its interaction with AtSLAH1 in Arabidopsis, but only under non-saline conditions. Here, we investigated the function of its homolog in P. cornutum , PcSLAH3, under saline conditions. The results showed that PcSLAH3 , which encodes a plasma membrane-localized protein, was expressed predominantly in the stelar tissues of roots, and exhibited significantly upregulated transcript levels in roots under NaCl treatments. Interactions were observed between PcSLAH3 and PcSLAH1, PcSLAH3, and AtSLAH1, as well as AtSLAH3 and PcSLAH1, suggesting the conservation of the SLAH1−SLAH3 interaction between salt-sensitive and salt-tolerant species. Heterologous expression of PcSLAH3 driven by a root stelar-specific promoter not only significantly increased the Cl - concentration, but also increased the Na + concentration in shoots of wild-type Arabidopsis or atslah3 mutant under salt treatment. This was accompanied by the upregulated expression of AtCLCg and AtNHX1 , which mediate the vacuolar compartmentalization of these two ions. Notably, PcSLAH3 outperformed AtSLAH3 in promoting root-to-shoot Cl - transport, potentially explaining the differences in Cl - transport capacity between xerophytes and glycophytes. These findings demonstrate that PcSLAH3 participates in Cl - transport from roots to shoots and is involved in regulating Cl - /Na + homeostasis in shoots under saline conditions.