Identification, expression analysis, and potential roles of microRNAs in the regulation of polysaccharide biosynthesis in Polygonatum cyrtonema Hua

MicroRNAs (miRNAs) are a group of endogenous small non-coding RNAs with important roles in plant growth, development, and metabolic processes. Polygonatum cyrtonema Hua (P. cyrtonema) is an important Chinese traditional medicinal herb with broad pharmacological functions, and polysaccharides are the main biological substance accumulated in the P. cyrtonema rhizome. However, regulation of the process of polysaccharide biosynthesis in P. cyrtonema remains largely unknown.To elucidate the miRNAs and their targets involved in polysaccharide biosynthesis in P. cyrtonema, four small RNA libraries were constructed from flower, leaf, rhizome, and root tissues and sequenced. A total of 69 conserved and 5 novel miRNAs were identified, of which 6 miRNAs (miR156a-5p, miR156f-5p, miR395a-5, miR396a-3p, miR396g-3p, and miR397-5p-1) were down-regulated and 7 miRNAs (miR160, miR160h-1, miR160e-5p, miR319b-1, miR319-1, miR319c-5p-3, and miR319c-1) were up-regulated in rhizomes compared with flower, leaf, and root tissues. Bioinformatics analysis showed that the predicted targets of these miRNAs were mostly transcription factors and functional genes enriched in metabolic and secondary metabolite biosynthetic pathways, and 7 genes and their paired miRNAs were identified in carbohydrate metabolism. qRT-PCR expression analysis demonstrated that 6 miRNAs and their targets involved in carbohydrate metabolism were existed a negative correlation in. P. cyrtonema tissues. MiR396a-3p and one of its target genes, abfA, were possibly involved in polysaccharide biosynthesis pathway. This is the first report on the identification of conserved and novel miRNAs and their potential targets in P. cyrtonema, thus providing molecular evidence for the role of miRNAs in the regulation of polysaccharide biosynthesis in P. cyrtonema.