Identification and characterization of microRNAs in phloem and xylem from ramie (Boehmeria nivea)

Ramie (Boehmeria nivea) is a widely cropped species in southern China due to its high economic value of natural fiber for industry. Development of phloem and xylem is key evidence for generating fiber. However, the MicroRNA (miRNA) profiles of phloem and xylem in ramie have not been reported yet. miRNA belong to a small RNA family which has been recognized as an important regulator for various biological processes. In the present study, we aimed to identify differently expressed miRNAs between phloem and xylem in adult ramie. The results showed that 137 and 122 unique conserved miRNAs were identified from phloem and xylem libraries, respectively. Meanwhile, 4 novel miRNAs were identified from ramie by miRDeep2. Of these miRNAs, 77 conserved miRNAs in ramie were differentially expressed. Among the differentially expressed miRNAs, 44 miRNAs and 33 miRNAs were up-regulated and down-regulated in phloem compared to that in xylem, respectively. The functions of differentially expressed miRNAs were associated with regulating the development and differentiation of phloem and xylem. The present study provides a glance of miRNA profiles for further understanding of miRNA role in ramie development.