miRNA-Based Drought Regulation in the Important Medicinal Plant Dendrobium huoshanense

Dendrobium is widely used in traditional Chinese medicine, and Dendrobium species show high diversity in potential adaptation to drought stress. Although miRNAs play crucial roles in regulating drought responses in plants, their functions in the drought response in Dendrobium remain unclear. To investigate the roles of miRNAs and their targets during drought stress, a small-RNA library from drought-treated Dendrobium huoshanense was constructed and sequenced. A total of 211 miRNAs were identified, comprising 115 known miRNAs and 96 novel miRNAs. Among them, 36 conserved and 33 novel miRNAs were characterized as differentially expressed miRNAs between drought and control samples. Target prediction, Gene Ontology (GO)-based functional classification, and Kyoto Encyclopedia of Genes and Genomes (KEGG)-based functional enrichment showed that drought-regulated miRNAs might play roles in the response to drought stress by targeting a series of stress-related genes. Importantly, integrated analysis of the miRNA transcriptome and qRT-PCR detection were performed to identify miR156, miR157d, and miR160a-5p and their targets (auxin response factor, cytokinin receptor, two-component response regulator, and DELLA protein gene). The results indicated that drought-regulated miRNAs might regulate their targets to respond to hormone signaling, thereby regulating the morphological and physiological responses of the plant to drought stress. Our results provide new insights into the complex regulatory network of medicinal plant responses to drought stress involving plant hormone signal transduction.