Effects of Exogenous (K(+)) Potassium Application on Plant Hormones in the Roots of Tamarix ramosissima under NaCl Stress

Abiotic stresses such as salt stress seriously affect the growth and yield of plants. Tamarix ramosissima Lcdcb (T. ramosissima) is a widely cultivated halophyte in saline-alkali areas of the world. As an essential element for plant growth and development, K(+) plays an irreplaceable role in improving the tolerance of plants to salt stress. However, there are few reports on the mechanism of K(+) in promoting plant hormones to reduce the damage of NaCl stress to T. ramosissima. In this study, we sequenced the transcriptome of the roots of T. ramosissima which were treated with exogenous potassium (K(+)) for 0 h, 48 h and 168 h under NaCl stress, according to the changes in the expression levels of differentially expressed genes (DEGs) in T. ramosissima roots. Key candidate genes and metabolic pathways related to plant hormones were mined for analysis and further verified by quantitative real-time PCR (qRT-PCR). The results showed that under NaCl stress for 48 h and 168 h, there were a large number of DEGs in the roots of T. ramosissima, and the expression levels changed over time. In particular, we found that 56 plant hormone-related genes were annotated to the Kyoto Encyclopedia of Genes and Genomes (KEGG) pathway, and with the increase of time, their expression levels were mainly up-regulated and involved in the related metabolic pathways to resist NaCl stress. It is worth noting that 7 DEGs related to abscisic acid (ABA), 28 DEGs related to auxin, 1 DEG related to ethylene (ET), and 1 DEG related to cytokinin (CK) were added within 168 h of exogenous potassium, and they were involved in alleviating the root damage of T. ramosissima under NaCl stress and played an important role. In addition, we found the plant hormone signal transduction pathway, which plays an important role in resistance to NaCl stress. As a result of this study, the molecular mechanism of plant hormones involved in applying exogenous potassium under NaCl stress is further understood, resulting in a better understanding of how exogenous potassium can alleviate the damage caused by NaCl under stress in T. ramosissima.