Identification of microRNA and analysis of target genes in Panax ginseng

Objective: Ginsenosides, polysaccharides and phenols, the main active ingredients in Panax ginseng, are not different significantly in content between 3 and 5 years old of ginsengs called Yuan ginseng and more than ten years old ones called Shizhu ginseng. The responsible chemical compounds cannot fully explain difference in efficacy between them. According to reports in Lonicerae Japonicae Flos(Jinyinhua in Chinese) and Glycyrrhizae Radix et Rhizoma(Gancao in Chinese), microRNA may play a role in efficacy,so we identified microRNAs in P. ginseng at the different growth years and analyzed their target genes.Methods: Using high-throughput sequencing, the RNA-Seq, small RNA-Seq and degradome databases of P. ginseng were constructed. The differentially expressed microRNAs was identified by qRT-PCR.Results: A total of 63,875 unigenes and 24,154,579 small RNA clean reads were obtained from the roots of P. ginseng. From these small RNAs, 71 miRNA families were identified by bioinformatics target prediction software, including 34 conserved miRNAs, 37 non-conserved miRNA families, as well as 179 target genes of 17 known miRNAs. Through degradome sequencing and computation, we finally verified 13 targets of eight miRNAs involved in transcription, energy metabolism, biological stress and disease resistance, suggesting the significance of miRNAs in the development of P. ginseng. Consistently, major miRNA targets exhibited tissue specificity and complexity in expression patterns.Conclusion: Differential expression microRNAs were found in different growth years of ginsengs(Shizhu ginseng and Yuan ginseng), and the regulatory roles and functional annotations of miRNA targets in P. ginseng need further investigation.