Identification, Molecular Cloning and Expression Analysis of Five RNA-Dependent RNA Polymerase Genes in <i>Salvia miltiorrhiza</i>

<div><p>RNA-dependent RNA polymerases (RDRs) act as key components of the small RNA biogenesis pathways and play significant roles in post-transcriptional gene silencing (PTGS) and antiviral defense. However, there is no information about the <i>RDR</i> gene family in <i>Salvia miltiorrhiza</i>, an emerging model medicinal plant with great economic value. Through genome-wide predication and subsequent molecular cloning, five full-length <i>S. miltiorrhiza RDR</i> genes, termed <i>SmRDR1</i>–<i>SmRDR5</i>, were identified. The length of <i>SmRDR</i> cDNAs varies between 3,262 (<i>SmRDR5</i>) and 4,130 bp (<i>SmRDR3</i>). The intron number of <i>SmRDR</i> genes varies from 3 (<i>SmRDR1, SmRDR3</i> and <i>SmRDR4</i>) to 17 (<i>SmRDR5</i>). All of the deduced SmRDR protein sequences contain the conserved RdRp domain. Moreover, SmRDR2 and SmRDR4 have an additional RRM domain. Based on the phylogenetic tree constructed with sixteen RDRs from <i>Arabidopsis</i>, rice and <i>S. miltiorrhiza</i>, plant RDRs may be divided into four groups (RDR1–RDR4). The RDR1 group contains an AtRDR and an OsRDR, while includes two SmRDRs. On the contrary, the RDR3 group contains three AtRDRs and two OsRDRs, but has only one SmRDR. <i>SmRDRs</i> were differentially expressed in flowers, leaves, stems and roots of <i>S. miltiorrhiza</i> and responsive to methyl jasmonate treatment and cucumber mosaic virus infection. The results suggest the involvement of <i>RDRs</i> in <i>S. miltiorrhiza</i> development and response to abiotic and biotic stresses. It provides a foundation for further studying the regulation and biological functions of <i>SmRDRs</i> and the biogenesis pathways of small RNAs in <i>S. miltiorrhiza</i>.</p>