Abstract
BackgroundArgonaute (AGO) is the core component of RNA-induced silencing complex. The AGO gene family has been analyzed in various plant species; however, there is no report about AGOs in the well-known Traditional Chinese Medicine (TCM) plant, Salvia miltiorrhiza.ResultsThrough a genome-wide analysis, we identified ten SmAGO genes in S. miltiorrhiza. Full-length cDNAs of all SmAGOs were subsequently cloned and sequenced. These SmAGOs were characterized using a comprehensive approach. Sequence features, gene structures and conserved domains were analyzed by the comparison of SmAGOs and AtAGOs. Phylogenetic relationships among AGO proteins from S. miltiorrhiza, Arabidopsis and rice were revealed. The expression levels of SmAGO genes in various tissues of S. miltiorrhiza were investigated. The results implied that some SmAGOs, such as SmAGO1, SmAGO2, SmAGO3, SmAGO7 and SmAGO10, probably played similar roles as their counterparts in Arabidopsis; whereas the others could be more species-specialized. It suggests the conservation and diversity of AGOs in plants. Additionally, we identified a total of 24 hairpin structures, representing six miRNA gene families, to be miRNA precursors. Using the modified 5′-RACE method, we confirmed that SmAGO1 and SmAGO2 were targeted by S. miltiorrhiza miR168a/b and miR403, respectively. It suggests the conservation of AGO1-miR168 and AGO2-miR403 regulatory modules in S. miltiorrhiza and Arabidopsis.ConclusionsThis is the first attempt to explore SmAGOs and miRNAs in S. miltiorrhiza. The results provide useful information for further elucidation of gene silencing pathways in S. miltiorrhiza.
Highlights
Argonaute (AGO) is the core component of RNA-induced silencing complex
* Correspondence: sflu@implad.ac.cn Institute of Medicinal Plant Development, Chinese Academy of Medical Sciences & Peking Union Medical College, No.151, Malianwa North Road, Haidian District, Beijing 100193, China and small interfering RNAs, based on the source of double-stranded RNA (dsRNA) [4]. miRNAs are produced from plant transcripts with internal stem-loop structures, whereas siRNAs are derived from transcripts with inverted-repeat sequence, dsRNAs copied from single-stranded RNA, over-lapping regions of bidirectional transcripts, or dsRNAs formed by virus replication
AGO proteins are central components of RNA-induced silencing complex (RISC) involved in small RNA (sRNA)-mediated RNA cleavage, translational repression and DNA methylation, some of them are regulated by sRNAs through the feedback mechanism
Summary
Argonaute (AGO) is the core component of RNA-induced silencing complex. The AGO gene family has been analyzed in various plant species; there is no report about AGOs in the well-known Traditional Chinese Medicine (TCM) plant, Salvia miltiorrhiza. The generated sRNA duplexes from dsRNAs are loaded into RNA-induced silencing complexes (RISCs) with Argonautes (AGOs) as the central components [5]. RISCs remove the star strand (known as miRNA* or siRNA*) of sRNA duplex and select the functional strand as a guide to interact with homologous RNA or DNA molecules for direct RNA cleavage, translational repression or DNA methylation [6,7]. Arabidopsis AGO1 is the most well-studied plant AGO gene It encodes the core component of RISCs associated with the action of miRNAs, trans-acting siRNAs (ta-siRNAs) and transgene-derived siRNAs [14]. AGO proteins are central components of RISCs involved in sRNA-mediated RNA cleavage, translational repression and DNA methylation, some of them are regulated by sRNAs through the feedback mechanism. The function and regulatory mechanism of AGO genes from plant species other than Arabidopsis is largely unknown
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