Research Progress on Molecular Mechanism of Salt Tolerance in Rice

Rice is one of the important grain crops in the world and is sensitive to salt stress. The increasingly serious salinization of paddy soils is becoming a potential risk to the safe production of rice. Salt stress can cause osmotic stress, ion toxicity and oxidative stress in rice plant, ultimately leading to a decrease in rice quality and yield. Due to the ability of rice roots to absorb salt and secrete organic acids as well as the growth characteristics of water holding in the early stage and drainage in rice paddies in the later stage, rice is also an excellent crop for improving saline soil. Therefore, cultivating new rice varieties of salt tolerant and improving rice salt tolerance can effectively enhance the production potential of saline farmland, which is important to food security in China and the world. In recent years, quantitative genetics and molecular marker technology have been continuously developed. Through genetic, biochemical and molecular biology methods, a large number of salt-tolerant related QTLs and genes have been excavated, which is of great benefit to analyze the molecular mechanism of salt tolerance in rice and improve the breeding efficiency of salt-tolerant rice through molecular marker-assisted selection, gene editing and other molecular means. Nevertheless, many cloned genes related to salt tolerance are difficult to be applied in rice breeding currently as most of them are obtained through reverse genetics methods and exhibit salt tolerance only under overexpression conditions, or these genes are recessive genes. The study summarized the recent progress in the identification and mining of salt-tolerant genes in rice, and reviewed the research progress on molecular mechanisms of salt tolerance in rice from four aspects: osmotic regulation of organic matter, regulation of ion absorption and transport, regulation of reactive oxygen removal by antioxidant system and regulation of hormone. The challenges of future researches on salt tolerance of rice were also discussed in order to provide some suggestions for molecular breeding of salt tolerance of rice in the future.