Heterologous expression of the Leymus chinensis metallothionein gene LcMT3 confers enhanced tolerance to salt stress in Escherichia coli, yeast, and Arabidopsis thaliana

Salinity is poisonous to various plant physiological processes and poses an increasingly severe threat to agricultural productivity worldwide. As a tactic to mitigate this issue, the hunt for salt-tolerance genes and pathways is intensifying. The low-molecular-weight proteins known as metallothioneins (MTs) can effectively reduce salt toxicity in plants. In seeking concrete evidence of its function under salt stress conditions, a unique salt-responsive metallothionein gene, LcMT3, was isolated from the extremely salt-enduring Leymus chinensis and heterologously characterized in Escherichia coli (E. coli), yeast (Saccharomyces cerevisiae), as well as Arabidopsis thaliana. Overexpression of LcMT3 imparted resistance to salt in E. coli cells and yeast, while the development of control cells was completely inhibited. Besides, transgenic plants expressing LcMT3 exhibited significantly enhanced salinity tolerance. They had higher germination rates and longer roots than their nontransgenic counterparts during NaCl tolerance. For several physiological indices of salt tolerance, transgenic lines reduced the accumulation of malondialdehyde (MDA), relative conductivity, and reactive oxygen species (ROS) in comparison to nontransgenic Arabidopsis. They also possessed increased concentrations of proline (Pro), relative water content, chlorophyll content, coupled with three more active antioxidant enzymes (superoxide dismutase (SOD), peroxidase (POD), and catalase (CAT)). Transgenic plants also accumulated less Na+ and maintained a lower Na+/K+ ratio than control, which can be attributable to the transgene's regulatory effect on transporter proteins such as salt overly sensitive (SOS) and Na+/H+ antiporter (NHX1), as demonstrated by qPCR experiments. Collectively, LcMT3 could have a vital function in salinity resistance and be an essential candidate protein for abiotic stress.