Authentication of medicinal herb Wikstroemia indica using novel DNA markers derived from the chloroplast genome sequences

The processed root of Wikstroemia indica, also known as Wikstroemiae Radix (WR), is known as a time-honored traditional herbal medicine demonstrating health-promoting properties. Although W. indica is valuable, its molecular information on this medicinal plant is limited. In this study, we reported the complete chloroplast (cp) genome sequences of W. indica and its congener, W. nutans, the latter of which is highly identical to W. indica in both their natural distributions and morphological characteristics. The cp genomes of W. indica and W. nutans were 151,746 bp and 149,776 bp in size, respectively, and were predicted to contain the same number of genes, including 78 protein-coding, 37 tRNA, and eight rRNA genes. Genome comparison of W. indica showed that mutational hotspots were present despite low intraspecific variations were detected between two different accessions. Although phylogenetic analyses revealed that the two closely-related species of Wikstroemia were sisters, presence of variations in the sequence and mutational hotspots demarcated these two species apart. To authenticate commercial WR products sold in the market, three sets of novel indel markers and two sets of novel DNA barcoding markers from the cp genome sequences were developed. However, only the indel marker ndhK-trnV and the DNA barcoding marker, ccsA-psaC were proven useful in discriminating W. indica from W. nutans; while the former is even capable to delimit W. indica from adulterants of other related species. The findings of this study are useful for the molecular development of W. indica and also contribute to the effort in species authentication, trade monitoring and drug regulation in the local herbal industry.