Arabidopsis microRNA expression regulation in a wide range of abiotic stress responses

Arabidopsis microRNA expression regulation was studied in a wide array of abiotic stresses such as drought, heat, salinity, copper excess/deficiency, cadmium excess and sulphur deficiency. A home-built RT-qPCR mirEX platform for the amplification of 289 Arabidopsis microRNA transcripts was used to study their response to abiotic stresses. Small RNA sequencing and Northern hybridization were performed to study the expression of mature microRNAs. In the case of common climate change related stresses such as drought, heat and salinity we observed broad induction of the level of primary miRNAs that was not observed at the level of microRNAs.. In the case of local soil pollution stresses, that are represented by heavy metal contaminations or deprivation of a specific micro- or macroelement, the transcriptional response of pri-miRNAs was quite limited but also not predictive to the level of the mature microRNA. This points to an essential role of posttranscriptional regulation of microRNAs expression. We found that the level of several microRNAs can be differentially regulated in early and late response to stress. New Arabidopsis microRNAs responsive to abiotic stresses were discovered. Three microRNAs: miR319a/b, miR319b.2, and miR400 have been found to be responsive in several abiotic stresses and thus can be regarded as a general stress-responsive microRNA species. Additionally, a new target for miR319b.2 – TBL10 has been experimentally confirmed. However, its level under different abiotic stresses is unchanged in comparison to control conditions. In the promoter region of the TBL10 gene we found the presence of many stress-responsive elements. We suggest that transcriptional induction resulting in the increase of transcript levels is downregulated by the increase of the miR319b.2 ultimately resulting in a stable level of TBL10 mRNA. Our experiments show the existence of a complex regulatory network involved in the microRNA level control that is necessary to fine-tune plant response to environmental cues. Overall design: Arabidopsis thaliana abiotic stress responses miRNAs: 30%SWC drought, 20%SWC drought, 0.5h heat (37°C), 6h heat (37°C), 24h NaCl [250mM] excess, 24h copper deficiency, 24h copper [10µM] excess, 24h cadmium [10µM] excess, 24h sulfur deficiency