Mechanism of high affinity potassium transporter (HKT) towards improved crop productivity in saline agricultural lands

Abstract

Glycophytic plants are susceptible to salinity and their growth is hampered in more than 40 mM of salt. Salinity not only affects crop yield but also limits available land for farming by decreasing its fertility. Presence of distinct traits in response to environmental conditions might result in evolutionary adaptations. A better understanding of salinity tolerance through a comprehensive study of how Na⁺ is transported will help in the development of plants with improved salinity tolerance and might lead to increased yield of crops growing in strenuous environment. Ion transporters play pivotal role in salt homeostasis and maintain low cytotoxic effect in the cell. High-affinity potassium transporters are the critical class of integral membrane proteins found in plants. It mainly functions to remove excess Na⁺ from the transpiration stream to prevent sodium toxicity in the salt-sensitive shoot and leaf tissues. However, there are large number of HKT proteins expressed in plants, and it is possible that these members perform in a wide range of functions. Understanding their mechanism and functions will aid in further manipulation and genetic transformation of different crops. This review focuses on current knowledge of ion selectivity and molecular mechanisms controlling HKT gene expression. The current review highlights the mechanism of different HKT transporters from different plant sources and how this knowledge could prove as a valuable tool to improve crop productivity.

Keywords: High-affinity potassium transporter (HKT); Ion homeostasis; Salinity stress; Sodium transport.

Fig. 1

Schematic representation of Na⁺ uptake and translocation in glycophytes via Na⁺ and/or K⁺ transporters and channels

Fig. 2

Regulatory mechanism of HKT genes. ABI4, ARR1, ARR12, AtbZIP24 (AtHKT1;1) and CML (MtHKT1;1) proteins negatively regulate expression of HKT genes. ARR1 and ARR12 in presence of cytokinin negatively regulates HKT gene. Osbhlh035, OsMYB106, MYBc and ERF are positive regulators of HKT gene. The TFs; ABI4 (abscisic acid insensitive 4); ARR (Arabidopsis response regulator); CML (calmodulin such as protein); ERF (ethylene response factor), control the respective HKT genes from different plant species, which are given in brackets