Overexpression of a Metallothionein 2A Gene from Date Palm Confers Abiotic Stress Tolerance to Yeast and Arabidopsis thaliana

Abstract

Although the date palm tree is an extremophile with tolerance to drought and certain levels of salinity, the damage caused by extreme salt concentrations in the soil, has created a need to explore stress-responsive traits and decode their mechanisms. Metallothioneins (MTs) are low-molecular-weight cysteine-rich proteins that are known to play a role in decreasing oxidative damage during abiotic stress conditions. Our previous study identified date palm metallothionein 2A (<i>PdMT2A</i>) as a salt-responsive gene, which has been functionally characterized in yeast and <i>Arabidopsis</i> in this study. The recombinant PdMT2A protein produced in <i>Escherichia coli</i> showed high reactivity against the substrate 5'-dithiobis-2-nitrobenzoic acid (DTNB), implying that the protein has the property of scavenging reactive oxygen species (ROS). Heterologous overexpression of <i>PdMT2A</i> in yeast (<i>Saccharomyces cerevisiae</i>) conferred tolerance to drought, salinity and oxidative stresses. The <i>PdMT2A</i> gene was also overexpressed in <i>Arabidopsis</i>, to assess its stress protective function in planta. Compared to the wild-type control, the transgenic plants accumulated less Na⁺ and maintained a high K⁺/Na⁺ ratio, which could be attributed to the regulatory role of the transgene on transporters such as HKT, as demonstrated by qPCR assay. In addition, transgenic lines exhibited higher chlorophyll content, higher superoxide dismutase (SOD) activity and improved scavenging ability for reactive oxygen species (ROS), coupled with a better survival rate during salt stress conditions. Similarly, the transgenic plants also displayed better drought and oxidative stress tolerance. Collectively, both in vitro and in planta studies revealed a role for <i>PdMT2A</i> in salt, drought, and oxidative stress tolerance.