Salinity stress in rice: Physiological and molecular mechanisms with a focus on the role of the hst1 gene and OsRR22 in enhancing salt tolerance

Salinity is a major abiotic stress that threatens global food security, particularly in arid and semi-arid regions. Rice ( Oryza sativa L.) is a stable food for over half of the world's population. Rising salinity levels in agricultural lands due to chlimate change and unsustainable irrigation practices are expected to impact nearly half of the world’s arable lands by 2050. This review focuses on the role of the hst1 gene, a mutant form of OsRR22 , in enhancing salinity tolerance in rice. The hst1 gene plays a crucial role in maintaining ion homeostasis, scavenging reactive oxygen species (ROS), and regulating stress-responsive signaling pathways, all of which are critical for mitigating the negative effects of salinity on rice plants. Under salt stress, the hst1 mutation enables rice plants to accumulate less sodium (Na + ) and more potassium (K + ), preserving cellular function and enhancing photosynthetic efficiency. Additionally, hst1 activates antioxidant enzymes such as superoxide dismutase (SOD), catalase (CAT), and glutathione reductase (GR), which protect cells from oxidative damage caused by ROS. The gene also modulates transcription factors that regulate downstream stress-response genes, contributing to improved growth and yield under saline conditions. By understanding the physiological and molecular mechanisms underlying hst1 -mediated salt tolerance, this review provides insights into breeding strategies for developing salt-tolerant rice varieties. Such advancements are essential for sustaining rice production in saline-affected regions and ensuring global food security in the face of climate change and population growth.