Arabidopsis microRNA162 (miRNA162) level regulation was studied under abiotic stresses, such as drought and salinity. The TaqMan® microRNA assay proved that A. thaliana miRNA162 level was elevated under these stresses, confirming its salt and drought responsiveness. The promoter region analyses of A. thaliana miRNA162a and b genes (MIR162a and MIR162b) identified numerous salinity and drought responsive elements. However, our results indicated that Arabidopsis MIR162a was presumably the main locus responsible for the mature ath-miRNA162 accumulation under the stresses tested, and the MIR162b was generally rather weakly expressed, both in control and under the stress conditions. The MIR162a structure was confirmed to be complex and the pri-miRNA162a hairpin structure was shown to span an alternative exon and an intron. The MIR162a transcription generated a few pri-miRNA162a splicing isoforms that could be functional and non-functional. Upon drought and salinity stresses, the regulation of the pri-miRNA162a alternative splicing pattern revealed an increase of a functional pri-miR162a isoform and a preferential distal polyA site selection under the stress conditions. Apart from the potential transcriptional regulation of the miRNA genes (MIRs) expression, the data obtained point to an essential role of posttranscriptional regulation of Arabidopsis microRNA162 level.
MicroRNAs are short molecules of 21-24 nt in length. They are present in all eukaryotic organisms and regulate gene expression by guiding posttranscriptional silencing of mRNAs. In plants, they are key players in signal transduction, growth and development, and in response to abiotic and biotic stresses. Barley (Hordeum vulgare) is an economically important monocotyledonous crop plant. Drought is the world's main cause of loss in cereal production. We have constructed a high-throughput Real-Time RT-qPCR platform for parallel determination of 159 barley primary microRNAs' levels. The platform was tested for two drought-and-rehydration-treated barley genotypes (Rolap and Sebastian). We have determined changes in the expression of primary microRNAs responding to mild drought, severe drought, and rehydration. Based on the results obtained, we conclude that alteration in the primary microRNA expression is relative to the stress's intensity. Mild drought and rehydration mostly decrease the pri-miRNA levels in both of the tested genotypes. Severe drought mainly induces the primary microRNA expression. The main difference between the genotypes tested was a much-stronger induction of pri-miRNAs in Rolap encountering severe drought. The primary microRNAs respond dynamically to mild drought, severe drought, and rehydration treatments. We propose that some of the individual pri-miRNAs could be used as drought stress or rehydration markers. The usage of the platform in biotechnology is also postulated.
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