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 AcHKT1 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.

Automated summary

The AcHKT1;2 gene plays a key role in mediating the entry of Na+ into salt bladders of A. canescens, facilitating continuous Na+ sequestration and ensuring the survival of plants in harsh saline environments.