Heterologous Expression of Salvia miltiorrhiza MicroRNA408 Enhances Tolerance to Salt Stress in Nicotiana benthamiana

Abstract

MicroRNAs (miRNAs) are a class of endogenous small RNAs that regulate the expression of target genes post-transcriptionally; they are known to play major roles in development and responses to abiotic stress. MicroRNA408 (miR408) is a conserved small RNA in plants; it was reported that miR408 genes were involved in abiotic stress in <i>Arabidopsis</i>. However, miR408 in <i>Salvia miltiorrhiza</i> has been rarely investigated. In this study, we cloned <i>Sm-MIR408</i>, the miR408 precursor sequence, and its promoter sequence from <i>S. miltiorrhiza</i> and the role in tolerance to salt stress is described. The effects of salt stress on miR408 expression were studied by using β-glucuronidase (GUS) staining. Our data indicated that transgenic tobacco overexpressing <i>Sm-MIR408</i> promoted seed germination and reduced the accumulation of reactive oxygen species under salt stress. Transcript levels of antioxidative genes, i.e., <i>NbSOD</i>, <i>NbPOD</i>, and <i>NbCAT</i>, and their enzyme activities increased in salinity-stressed transgenic tobacco plants, suggesting a better antioxidant system to cope the oxidative damage caused by salinity stress. Taken together, these findings indicated that miR408 functions in positive responses to salt tolerance in tobacco.