AcHKT1;2 is a candidate transporter mediating the influx of Na + into the salt bladder of Atriplex canescens

Purpose Atriplex canescens adapts to saline soils by sequestering excessive Na + in salt bladders on the surface of aerial tissues, which is a complex comprising epidermal cells (ECs), stalk cells (SCs) and epidermal bladder cells (EBCs). However, the mechanism of how Na + enters salt bladders of A. canescens is not yet clear. We previously identified two A. canescens HKT1 genes that might be related to Na + sequestration in salt bladders. The aim of this study was to evaluate the function of AcHKT1 genes in Na + secretion. Results Two A cHKT1 genes were cloned; AcHKT1;1 was largely expressed in roots, while AcHKT1;2 was mainly expressed in shoots and strongly induced by NaCl. Heterologous expression of AcHKT1;2 aggravated the Na + -sensitive phenotype in yeast. This result was further confirmed in Xenopus system, in which AcHKT1;2 exerted high selectivity for Na + , indicating that AcHKT1;2 functions as a plasma membrane-localized Na + transporter and mediates robust Na + influx at the cellular level. Interestingly, AcHKT1;2 expression in leaves was significantly reduced once salt bladders were removed from the leaf surfaces; in particular, it had the greatest impact on the expression in mature leaves with the strongest activity toward ion secretion, suggesting that AcHKT1;2 was predominantly expressed in the EC-SC-EBC complex of A. canescens leaves. Conclusions AcHKT1;2 is a key candidate transporter involved in mediating the entry of Na + into A. canescens EBCs, thereby facilitating continuous Na + sequestration in EBCs to ensure the survival of plants in harsh saline environments.