Overexpression of a Thioredoxin-Protein-Encoding Gene, <i>MsTRX</i>, from <i>Medicago sativa</i> Enhances Salt Tolerance to Transgenic Tobacco

Abstract

Thioredoxin (TRX) is a small molecule protein that participates in the redox process and plays a decisive role in various functions of plants. However, the role of TRX in Medicago sativa (alfalfa), a widely cultivated perennial herb of legume, is still poorly understood. Here, we isolated MsTRX from alfalfa and determined the characteristics in improving salt tolerance by assaying the phenotype and physiological changes and the expression of stress-response genes in transgenic tobacco. The expression of MsTRX was similar in alfalfa roots, leaves, and inflorescences, and was downregulated in response to cold, drought, and salt treatment. The overexpression of MsTRX in tobacco promoted the accumulation of soluble sugar (SS) and proline; enhanced the activity of peroxidase (POD); and induced the upregulation of beta-amylase 1 (BAM1), lipid-transfer protein 1 (LTP1), candidate signal molecules/sensor relay proteins (CBSX3), superoxide dismutase [Cu-Zn] (Cu/Zn-SOD), superoxide dismutase [Mn] (Mn-SOD), protein gamma response 1 (GR1), dehydrin DHN1-like (ERD10B), and serine/threonine-protein kinase (SnRK2), as well as the downregulation of phyB activation-tagged suppressor1 (BAS1) and serine/threonine-protein kinase that phosphorylates LHCII protein 7 (STN7) under salt stress. These results indicated that MsTRX improves salt tolerance via maintaining osmotic homeostasis, scavenging reactive oxygen species (ROS), and regulating the transcription of stress-response genes in plants. In our study, we provided a new understanding of how MsTRX improves salt stress in plants and how MsTRX can be included in future breeding programs to improve salt tolerance in alfalfa.

Keywords

• alfalfa
• thioredoxin
• salt stress
• phenotype assay
• physiological change
• stress-response genes