Development of DNA Barcodes and Optimization of DNA Isolation and PCR Protocols for a Medicinal Plant Plectranthus hadiensis

The medicinal plant Plectranthus hadiensis of Lamiaceae is reported for various biological properties. This plant is substituted in herbal industry by other plants of the same genus due to misidentification. Therefore, the objective of this study was to develop DNA barcodes to discriminate Sri Lankan P. hadiensis from adulterant Plectranthus spp. As DNA barcodes, matK, rbcL and trnH-psbA chloroplast DNA regions were amplified and sequenced. This study also attempted modification of Cetyltrimethylammonium Bromide (CTAB) based DNA isolation and PCR protocols, as genomic DNA from leaves indicated contaminating metabolites that prevented PCR. The barcode sequences resulted in this study were deposited in GenBank nucleotide database. To verify if these barcodes are competent for family or genus assignment of P. hadiensis, the rbcL sequence of P. hadiensis was compared with the rbcL sequences available in the GenBank nucleotide database of the species of the order Lamiales and family Lamiaceae. Comparison of rbcL sequences identified single nucleotide polymorphism among Plectranthus species with a considerable interspecific divergence suggesting that rbcL could serve as a barcode for P. hadiensis.