Potential of HKT, NHX, and HAK gene transfer responsive to salt stress in rice (Oryza sativa L.)

Rice (Oryza sativa L.) is one of the most important staple cereal crops globally, and maximizing its yield is essential for ensuring food security. However, increasing soil salinity is a major abiotic stress that significantly restricts rice cultivation, productivity, and overall yield, particularly in coastal regions such as Bangladesh. Globally, salt stress affects nearly one-third of irrigated croplands and disrupts rice physiological processes, causing substantial yield losses even under moderate stress conditions. Genetic improvement has emerged as an effective strategy to enhance salt tolerance, as demonstrated by studies involving Saltol quantitative trait loci (QTL) introgression and transgenic overexpression of key genes. This systematic review summarizes the physiological impacts of salt stress on rice and highlights the critical roles of three gene families HKT (High-Affinity K⁺ Transporters), NHX (Na⁺/H⁺ Antiporters), and HAK (High-Affinity K⁺ Transporters)—in maintaining ionic homeostasis under saline environments through Na⁺ exclusion, vacuolar sequestration, and K⁺ uptake. In addition, the review examines gene transfer approaches, including transgenic methods, CRISPR/Cas9-mediated genome editing, and QTL introgression. Emerging strategies such as gene stacking, synthetic promoter development, and AI-assisted breeding are also discussed as future avenues to develop highly salt-tolerant rice varieties. Overall, integrating molecular innovations with advanced breeding techniques offers sustainable solutions to mitigate salinity stress and safeguard global rice production under changing climatic conditions.