LbHKT1;1 Negatively Regulates Salt Tolerance of Limonium bicolor by Decreasing Salt Secretion Rate of Salt Glands

ABSTRACT The HKT‐type proteins have been extensively studied and have been shown to play important roles in long‐distance Na + transport, maintaining ion homoeostasis and improving salt tolerance in plants. However, there have been no reports on the types, characteristics and functions of HKT‐type proteins in Limonium bicolor , a recretohalophyte species with the typical salt gland structure. In this study, five LbHKT genes were identified in L. bicolor , all belonging to subfamily 1 (HKT1). There are many cis ‐acting elements related to abiotic/biotic stress response on the promoters of the LbHKT genes. LbHKT1;1 was investigated in detail. Subcellular localization results showed that LbHKT1;1 is targeted to the plasma membrane. Functional analysis in yeast showed that LbHKT1;1 has a higher tolerance than AtHKT1;1 under high Na + conditions. Silencing and overexpression of the LbHKT1;1 gene in L. bicolor showed that LbHKT1;1 negatively regulates salt secretion by the salt glands. Further experiments showed that LbbZIP52 can specifically bind to the ABRE element in the LbHKT1;1 promoter and regulate the expression of the LbHKT1;1 gene and is involved in the negative regulation of the salt secretion capacity of L. bicolor . This study demonstrates for the first time that the HKT‐type protein is involved in salt secretion by salt glands and provides a new perspective on the function of HKT‐type proteins under salt stress conditions.