Arabidopsis microRNA expression regulation was studied in a wide array of abiotic stresses such as drought, heat, salinity, copper excess/deficiency, cadmium excess, and sulfur 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, Northern hybridization, and TaqMan® microRNA assays were performed to study the abundance of mature microRNAs. A broad response on the level of primary miRNAs (pri-miRNAs) was observed. However, stress response at the level of mature microRNAs was rather confined. The data presented show that in most instances, the level of a particular mature miRNA could not be predicted based on the level of its pri-miRNA. This points to an essential role of posttranscriptional regulation of microRNA expression. New Arabidopsis microRNAs responsive to abiotic stresses were discovered. Four microRNAs: miR319a/b, miR319b.2, and miR400 have been found to be responsive to several abiotic stresses and thus can be regarded as general stress-responsive microRNA species.

Introns of plant pri-miRNAs enhance miRNA biogenesismiRNA-proximal introns and functional splice sites are required for the accumulation of normal levels and the activity of mature miRNAs in Arabidopsis.

SummaryDeveloping new strategies for crop plants to respond to drought is crucial for their innovative breeding. The down-regulation of nuclear cap-binding proteins in Arabidopsis renders plants drought tolerant. The CBP80 gene in the potato cultivar Desiree was silenced using artificial microRNAs. Transgenic plants displayed a higher tolerance to drought, ABA-hypersensitive stomatal closing, an increase in leaf stomata and trichome density, and compact cuticle structures with a lower number of microchannels. These findings were correlated with a higher tolerance to water stress. The level of miR159 was decreased, and the levels of its target mRNAs MYB33 and MYB101 increased in the transgenic plants subjected to drought. Similar trends were observed in an Arabidopsis cbp80 mutant. The evolutionary conservation of CBP80, a gene that plays a role in the response to drought, suggests that it is a candidate for genetic manipulations that aim to obtain improved water-deficit tolerance of crop plants.

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