Hemant Kumar Singh

DNA barcoding of endangered Indian Paphiopedilum species

The indiscriminate collections of Paphiopedilum species from the wild for their exotic ornamental flowers have rendered these plants endangered. Although the trade of these endangered species from the wild is strictly forbidden, it continues unabated in one or other forms that elude the current identification methods. DNA barcoding that offers identification of a species even if only a small fragment of the organism at any stage of development is available could be of great utility in scrutinizing the illegal trade of both endangered plant and animal species. Therefore, this study was undertaken to develop DNA barcodes of Indian species of Paphiopedilum along with their three natural hybrids using loci from both the chloroplast and nuclear genomes. The five loci tested for their potential as effective barcodes were RNA polymerase‐β subunit (rpoB), RNA polymerase‐β’ subunit (rpoC1), Rubisco large subunit (rbcL) and maturase K (matK) from the chloroplast genome and nuclear ribosomal internal transcribed spacer (nrITS) from the nuclear genome. The intra‐ and inter‐specific divergence values and species discrimination rates were calculated by Kimura 2 parameter (K2P) method using mega 4.0. The matK with 0.9% average inter‐specific divergence value yielded 100% species resolution, thus could distinguish all the eight species of Paphiopedilum unequivocally. The species identification capability of these sequences was further confirmed as each of the matK sequences was found to be unique for the species when a blast analysis of these sequences was carried out on NCBI. nrITS, although had 4.4% average inter‐specific divergence value, afforded only 50% species resolution. DNA barcodes of the three hybrids also reflected their parentage.

The loci recommended as universal barcodes for plants on the basis of floristic studies may not work with congeneric species as exemplified by DNA barcoding of Dendrobium species

BackgroundBased on the testing of several loci, predominantly against floristic backgrounds, individual or different combinations of loci have been suggested as possible universal DNA barcodes for plants. The present investigation was undertaken to check the applicability of the recommended locus/loci for congeneric species with Dendrobium species as an illustrative example.ResultsSix loci, matK, rbcL, rpoB, rpoC1, trnH-psbA spacer from the chloroplast genome and ITS, from the nuclear genome, were compared for their amplification, sequencing and species discrimination success rates among multiple accessions of 36 Dendrobium species. The trnH-psbA spacer could not be considered for analysis as good quality sequences were not obtained with its forward primer. Among the tested loci, ITS, recommended by some as a possible barcode for plants, provided 100% species identification. Another locus, matK, also recommended as a universal barcode for plants, resolved 80.56% species. ITS remained the best even when sequences of investigated loci of additional Dendrobium species available on the NCBI GenBank (93, 33, 20, 18 and 17 of ITS, matK, rbcL, rpoB and rpoC1, respectively) were also considered for calculating the percent species resolution capabilities. The species discrimination of various combinations of the loci was also compared based on the 36 investigated species and additional 16 for which sequences of all the five loci were available on GenBank. Two-locus combination of matK+rbcL recommended by the Plant Working Group of Consortium for Barcoding of Life (CBOL) could discriminate 86.11% of 36 species. The species discriminating ability of this barcode was reduced to 80.77% when additional sequences available on NCBI were included in the analysis. Among the recommended combinations, the barcode based on three loci - matK, rpoB and rpoC1- resolved maximum number of species.ConclusionsAny recommended barcode based on the loci tested so far, is not likely to provide 100% species identification across the plant kingdom and thus is not likely to act as a universal barcode. It appears that barcodes, if based on single or limited locus(i), would be taxa specific as is exemplified by the success of ITS among Dendrobium species, though it may not be suitable for other plants because of the problems that are discussed.

Evaluating five different Loci (rbcL, rpoB, rpoC1, matK and ITS) for DNA Barcoding of Indian Orchids

Orchidaceae, one of the largest families of angiosperms, is represented in India by 1600 species distributed in diverse habitats. Orchids are in high demand owing to their beautiful flowers and therapeutic properties. Overexploitation and habitat destruction have made many orchid species endangered. In the absence of effective identification methods, illicit trade of orchids continues unabated. Considering DNA barcoding as a potential identification tool, species discrimination capability of five loci, ITS, matK, rbcL, rpoB, and rpoC1, was tested in 393 accessions of 94 Indian orchid species belonging to 47 genera, including one listed in Appendix I of CITES and 26 medicinal species. ITS provided the highest species discrimination rate of 94.9%. While, among the chloroplast loci, matK provided the highest species discrimination rate of 85.7%. None of the tested loci individually discriminated 100% of the species. Therefore, multi-locus combinations of up to five loci were tested for their species resolution capability. Among two-locus combinations, the maximum species resolution (86.7%) was provided by ITS+matK. ITS and matK sequences of the medicinal orchids were species specific, thus providing unique molecular identification tags for their identification and detection. These observations emphasize the need for the inclusion of ITS in the core barcode for plants, whenever required and available.

DNA Barcodes Distinguish Withania somnifera and Withania ashwagandha

On the basis of morphology, chemical profiling, crossing ability, amplified fragment length polymorphism and comparison of nucleotide sequences of nuclear ribosomal internal transcribed spacer (ITS), the cultivated form of Withania somnifera, a species of therapeutic value, has been circumscribed as a new species, Withania ashwagandha. The present study was undertaken to ascertain whether the two species can be distinguished on the basis of DNA barcoding. Six barcode loci, ITS, ITS2, matK (maturase K), rbcL (ribulose-bisphosphate carboxylase/oxygenase, large subunit), rpoC1 (RNA polymerase-β′ subunit, main catalytic subunit) and trnH-psbA spacer (transfer RNA for histidine-photosystem II protein D1 spacer) from W. somnifera, W. ashwagandha, their hybrid, and ‘ashwagandha’ market samples were amplified, sequenced, and compared. ITS, ITS2 and matK distinguished two species on the basis of phylogenetic tree method. Likewise, BLAST 1 analysis based on ITS, ITS2, matK, and rbcL individually discriminated two species. However, on the basis of Kimura 2 Parameter distances, two species could not be distinguished as the requirement of a distinct barcode gap—the highest intraspecific distance being lower than the lowest interspecific distance—was not met by any of the loci. If compared by character-based method, ITS, ITS2 and matK sequences of the two species had distinct diagnostic nucleotides (pure character attributes) at nine, four and one positions, respectively. Interestingly, all market samples co-segregated and shared character attributes with W. ashwagandha.