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The members of the microRNA (miRNA) family exert essential roles in modulating plant growth and development as well as responses to diverse stresses, through negatively regulating their target genes at posttranscriptional or translational levels. In this study, we characterized taemiR9674a, a miRNA member in T. aestivum, in mediating plant responses to drought and salt stresses. Seven genes in total were predicted to act as the targets of tae-miR9674a via modulation of transcript cleavage. The transcripts of tae-miR9674a in roots and leaves were response to both stresses of drought and salt, displaying to be gradually upregulated following the progression of a 27-h regime of above stress treatments. The transgenic tobacco lines of tae-miR9674a exhibited modified growth traits under drought and salt treatments. Of these, the line with miRNA overexpression (i.e., Sen 1) improved drastically on plant biomass, leaf area, and root length, whereas that with its knockdown expression (Anti 1) significantly alleviated on above growth traits compared with wild type. The modified stress responses of tae-miR9674a were shown to be closely associated with the role of miRNA in regulating a suite of physiological parameters, of which Sen 1 displayed improved osmotic stress defensive-related traits, such as fastened stomata closing rate, increased leaf water retention capacity, enhanced osmolytes contents, and elevated antioxidant enzyme (AE) activities. The expression of NtP5CS1 involving proline biosynthesis and NtFeSOD, NtCAT1 and NtPOD4, the AE genes involved in modulating ROS homeostasis, was upregulated in Sen 1 upon drought and salt stresses, suggesting their involvement in miRNA-mediated plant drought and salt responses. Transcriptome analysis indicated that tae-miR9674a leads to modified expression of quantities of genes that functionally associate with GO terms "biological process", "cellular component", and "molecular function", which are overrepresented by the biochemical pathways of phytohormones (i.e., ethylene and jasmonic acid), salt response, salt/drought osmotic stress response through abscisic acid-dependent pathway and reactive oxygen species (ROS) homeostasis. Our investigation suggested that tae-miR9674a is an essential mediator in plant osmotic stress tolerance by positively regulating osmotic stress acclimation, cellular ROS homeostasis, and related defensive processes. [ABSTRACT FROM AUTHOR]

Plant miRNA members mediate diverse biological processes through regulating target genes at the posttranscriptional or translational level. In this study, tobacco miRNA NtMIR167a and its targets NtARF6 or NtARF8, two auxin response factor (ARF) encoding genes, were subjected to functional evaluation in mediating the plant growth and Pi-starvation response. NtMIR167a showed induced expression in root tissues upon Pi starvation and whose Pi-deprived upregulated expression was restored gradually upon the Pi normal recovery treatment. Conversely, NtARF6 and NtARF8 displayed inverse expression patterns to this miRNA upon low-Pi stress and the Pi recovery treatment, suggesting their regulation under the miRNA at posttranscriptional level. Trangene analysis revealed that the lines with NtMIR167a overexpression and those with NtARF6 and NtARF8 knockdown exhibited modified phenotypes and Pi-associated traits with respect to wild type under both P normal and Pi starvation conditions, together with altered reactive oxygen species (ROS)-associated parameters. Expression analysis revealed that a set of antioxidant enzyme (AE) genes display reduced transcripts in the Pi-deprived lines overexpressing TaMIR167a and knockdown of NtARF6 and NtARF8, suggesting the AE gene expression impacting on the lowered AE activities of transgenic lines. Transcriptome analysis on the NtMIR167 overexpression line revealed a transcriptional variation on quantities of genes that are categorized into diverse functional groups, suggesting that the miRNA/target module-mediated plant growth and Pi starvation response are associated with modulated transcript profiling initiated by auxin signaling controlled by ARF6 and ARF8. Additionally, NtPT1 and NtPT2, two phosphate transporter (PT) genes of tobacco, exhibited downregulated expression in lines overexpressing NtMIR167a or those with knockdown of NtARF6 and NtARF8; antisense expression of these PT genes resulted in reduced P accumulation and inhibited plant growth under Pi starvation treatment. Our results together confirmed that NtMIR167a/NtARF6(8) modules are crucial in mediating plant growth and Pi starvation adaptation via regulating various biological processes including ROS homeostasis and Pi acquisition. [ABSTRACT FROM AUTHOR]