Abstract
Forsythia suspensa is an important medicinal plant and traditionally applied for the treatment of inflammation, pyrexia, gonorrhea, diabetes, and so on. However, there is limited sequence and genomic information available for F. suspensa. Here, we produced the complete chloroplast genomes of F. suspensa using Illumina sequencing technology. F. suspensa is the first sequenced member within the genus Forsythia (Oleaceae). The gene order and organization of the chloroplast genome of F. suspensa are similar to other Oleaceae chloroplast genomes. The F. suspensa chloroplast genome is 156,404 bp in length, exhibits a conserved quadripartite structure with a large single-copy (LSC; 87,159 bp) region, and a small single-copy (SSC; 17,811 bp) region interspersed between inverted repeat (IRa/b; 25,717 bp) regions. A total of 114 unique genes were annotated, including 80 protein-coding genes, 30 tRNA, and four rRNA. The low GC content (37.8%) and codon usage bias for A- or T-ending codons may largely affect gene codon usage. Sequence analysis identified a total of 26 forward repeats, 23 palindrome repeats with lengths >30 bp (identity > 90%), and 54 simple sequence repeats (SSRs) with an average rate of 0.35 SSRs/kb. We predicted 52 RNA editing sites in the chloroplast of F. suspensa, all for C-to-U transitions. IR expansion or contraction and the divergent regions were analyzed among several species including the reported F. suspensa in this study. Phylogenetic analysis based on whole-plastome revealed that F. suspensa, as a member of the Oleaceae family, diverged relatively early from Lamiales. This study will contribute to strengthening medicinal resource conservation, molecular phylogenetic, and genetic engineering research investigations of this species.
Highlights
Forsythia suspensa (Thunb.) Vahl, known as “Lianqiao” in Chinese, is a well-known traditional Asian medicine that is widely distributed in many Asian and European countries [1]
Most cp genomes of higher plants have been found to have a typical quadripartite structure composed of an large single copy (LSC) region and an small single copy (SSC) region interspersed between the IRa/b region [5]
The complete cp genome of F. suspensa has a total length of 156,404 bp, with a pair of IRs of 25,717 bp that separate an LSC region of 87,159 bp and an SSC region of 17,811 bp (Figure 1)
Summary
Forsythia suspensa (Thunb.) Vahl, known as “Lianqiao” in Chinese, is a well-known traditional Asian medicine that is widely distributed in many Asian and European countries [1]. The extract of the dried fruit has long been used to treat a variety of diseases, such as inflammation, pyrexia, gonorrhea, tonsillitis, and ulcers [2]. Due to high-throughput capabilities and relatively low costs, next-generation sequencing techniques have made it more convenient to obtain a large number of cp genome sequences [7]. After the first complete cp DNA sequences were reported in Nicotiana tabacum [8] and Marchantia polymorpha [9], complete cp DNA sequences of numerous plant species were determined [6,10,11,12]. Approximately 1300 plant cp genomes are publicly available as part of the National Center for Biotechnology Information (NCBI) database
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