miR398 and miR395 are involved in response to SO2 stress in Arabidopsis thaliana.

Sulfur dioxide (SO2) is a common air pollutant that has adverse effects on plants. MicroRNAs (miRNAs) are small noncoding RNA that play critical roles in plant development and stress response. In this study, we found that two miRNAs, miR398 and miR395, were differentially expressed in Arabidopsis shoots under SO2 stress. The expression of miR398 was down-regulated, and the transcript levels of its target genes, Cu/Zn superoxide dismutases (CSD1 and CSD2), were increased during SO2 exposure. The activity of superoxide dismutase (SOD), one of the major antioxidant enzymes, was enhanced with the increase in the CSD transcript level, suggesting an important role of miR398 in response to SO2-induced oxidative stress. Meanwhile, the expression of miR395 was increased, and the transcript levels of its target genes, ATP sulfurylases (APS3 and APS4) and a low-affinity sulfate transporter (SULTR2;1), were decreased in Arabidopsis shoots, showing that miR395 played important roles in the regulation of sulfate assimilation and translocation during SO2 exposure. The content of glutathione (GSH), an important sulfur-containing antioxidant, was enhanced with the changes in sulfur metabolism in Arabidopsis shoots under SO2 stress. These results showed that both miR398 and miR395 were involved in protecting plants from oxidative damage during SO2 exposure. Many stress-responsive cis-elements were found in the promoter regions of MIR398 and MIR395, suggesting that these miRNAs might respond to various environmental conditions, including SO2 stress. Overall, our study provides an insight into the regulatory roles of miRNAs in response to SO2 stress in plants, and highlights the molecular mechanisms of plant adaptation to environmental stress.