A Novel miRNA Sponge Form Efficiently Inhibits the Activity ofmiR393 and Enhances the Salt Tolerance and ABA Insensitivity in Arabidopsis thaliana

MicroRNAs (miRNAs) regulate gene expression at the post-transcriptional level in eukaryotes by directing target mRNAs for degradation or by repressing translation. MicroRNAs are involved in many processes, including development, metabolism, and stress responses. MicroRNA miR393 is highly conserved and closely related to abiotic stresses. Its targets include the auxin receptors transport inhibitor response 1 and auxin related F-box proteins in different plants. In the present study, a miR393 sponge form was constructed and over-expressed in Arabidopsis thaliana under the control of the CaMV 35S promoter. The quantitative PCR analysis indicated that the transcript of mature AtmiR393 was inhibited in transgenic plants. The expression level of miR393 target genes AtTIR1, AtAFB1, AtAFB2, and AtAFB3 in transgenic plants was higher than the wild-type plants. Under high salt and abscisic acid (ABA) stresses, the transgenic plants showed a higher germination rate, longer root length, higher chloroplast content, and lower death rate than wild-type plants. The overall results indicated that overexpression of the miR393 sponge enhanced salt tolerance and ABA insensitivity in Arabidopsis.