Application of DNA Barcodes in Asian Tropical Trees--A Case Study from Xishuangbanna Nature Reserve, Southwest China

Exploring DNA barcode for accurate identification of threatened Aconitum L. species from Western Himalaya

BACKGROUND

Aconitum species, belonging to Ranunculaceae, have high medicinal importance but due to their overexploitation come under IUCN (International Union for Conservation of Nature) red list. The precise identification of the Aconitum species is equally important because they are used in herbal formulations. The present study aimed to develop an efficient DNA barcode system for the authentic identification of Aconitum species.

METHODS AND RESULTS

A set of 92 barcode gene sequences (including 12 developed during the present study and 80 retrieved from NCBI) of 5 Aconitum species (A. heterophyllum, A. vialoceum, A. japonicum, A. napellus, and A. stapfianum) were analyzed using three methods (tree-based, distance-based, and similarity-based) for species discrimination. The PWG-distance method was found most effective for species discrimination. The discrimination rate of PWG- distance ranged from 33.3% (rbcL + trnH-psbA) to 100% (ITS, rbcL + ITS, ITS + trnH-psbA and rbcL + ITS + trnH-psbA). Among DNA barcodes and their combinations, the ITS marker had the highest degree of species discrimination (NJ-40%, PWG-100% and BLAST-40%), followed by trnH-psbA (NJ-20%, PWG-60% and BLAST-20%). ITS also had higher barcoding gap as compared to other individual barcodes and their combinations. Further, we also analyzed six Aconitum species (A. balfourii, A. ferox, A. heterophyllum, A. rotundifolium, A. soongaricum and A. violaceum) existing in Western Himalaya. These species were distinguished clearly through tree-based method using the ITS barcode gene with 100% species resolution.

CONCLUSION

ITS showed the best species discrimination power and was used to develop species-specific barcodes for Aconitum species. DNA barcodes developed during the present study can be used to identify Aconitum species.

A DNA barcode library for woody plants in tropical and subtropical China

The application of DNA barcoding has been significantly limited by the scarcity of reliable specimens and inadequate coverage and replication across all species. The deficiency of DNA barcode reference coverage is particularly striking for highly biodiverse subtropical and tropical regions. In this study, we present a comprehensive barcode library for woody plants in tropical and subtropical China. Our dataset includes a standard barcode library comprising the four most widely used barcodes (rbcL, matK, ITS, and ITS2) for 2,520 species from 4,654 samples across 49 orders, 144 families, and 693 genera, along with 79 samples identified at the genus level. This dataset also provides a super-barcode library consisting of 1,239 samples from 1,139 species, 411 genera, 113 families, and 40 orders. This newly developed library will serve as a valuable resource for DNA barcoding research in tropical and subtropical China and bordering countries, enable more accurate species identification, and contribute to the conservation and management of tropical and subtropical forests.

Root-associated fungal communities are influenced more by soils than by plant-host root traits in a Chinese tropical forest

Forest fungal communities are shaped by the interactions between host tree root systems and the associated soil conditions. We investigated how the soil environment, root morphological traits, and root chemistry influence root-inhabiting fungal communities in three tropical forest sites of varying successional status in Xishuangbanna, China. For 150 trees of 66 species, we measured root morphology and tissue chemistry. Tree species identity was confirmed by sequencing rbcL, and root-associated fungal (RAF) communities were determined using high-throughput ITS2 sequencing. Using distance-based redundancy analysis and hierarchical variation partitioning, we quantified the relative importance of two soil variables (site average total phosphorus and available phosphorus), four root traits (dry matter content, tissue density, specific tip abundance, and forks), and three root tissue elemental concentrations (nitrogen, calcium, and manganese) on RAF community dissimilarity. The root and soil environment collectively explained 23% of RAF compositional variation. Soil phosphorus explained 76% of that variation. Twenty fungal taxa differentiated RAF communities among the three sites. Soil phosphorus most strongly affects RAF assemblages in this tropical forest. Variation in root calcium and manganese concentrations and root morphology among tree hosts, principally an architectural trade-off between dense, highly branched vs less-dense, herringbone-type root systems, are important secondary determinants.

Distinguishing features of Lycium L. species (family Solanaceae) distributed in Egypt based on their anatomical, metabolic, molecular, and ecological characteristics

Among the 70-80 species of the genus Lycium (family Solanaceae) disjunctly distributed around the world, only three are frequently distributed in different locations in Egypt. Due to the morphological similarities between these three species, there is a need for alternative tools to distinguish them. Thus, the objective of this study was to revise the taxonomic features of Lycium europaeum L., Lycium shawii Roem. & Schult., and Lycium schweinfurthii var. aschersonii (Dammer) Feinbrun in consideration of their anatomical, metabolic, molecular, and ecological characteristics. In addition to analysis of their anatomical and ecological features, DNA barcoding was performed for molecular characterization through internal transcribed spacer (ITS) sequencing and start codon targeted (SCoT) markers. Furthermore, metabolic profiling of the studied species was conducted based on gas chromatography-mass spectrometry (GC-MS). The observed anatomical features of the adaxial and abaxial epidermal layers, type of mesophyll, crystals, number of palisade and spongy layers, and the vascular system showed variations between the studied species. Beyond this, the anatomy of the leaves showed an isobilateral structure in the studied species, without distinct differences. Species were molecularly identified in terms of ITS sequences and SCoT markers. The ITS sequences were deposited in GenBank with accession numbers ON149839.1, OP597546.1, and ON521125.1 for L. europaeum L., L. shawii, and L. schweinfurthii var. aschersonii, respectively. The sequences showed variations in GC content between the studied species; this was 63.6% in L. europaeum, 61.53% in L. shawii, and 63.55% in L. schweinfurthii var. aschersonii. A total of 62 amplified fragments, including 44 polymorphic fragments with a ratio of 70.97%, were obtained in the SCoT analysis, as well as unique amplicons in L. europaeum L., shawii, and L. schweinfurthii var. aschersonii of 5, 11, and 4 fragments, respectively. Through GC-MS profiling, 38 compounds were identified with clear fluctuations in the extracts of each species. Of these, 23 were distinguishing chemicals that could help in chemical identification of the extracts of the studied species. The present study succeeds in identifying alternative clear and diverse characteristics that can be used to distinguish between L. europaeum, L. shawii, and L. schweinfurthii var. aschersonii.

Interspecific and intraspecific analysis of Selinum spp. collected from Indian Himalayas using DNA barcoding

BACKGROUND

DNA barcoding is a powerful method for phylogenetic mapping and species identification. However, recent research has come to a consistent conclusion about the universality of DNA barcoding. We used matK and rbcL markers to test the universality of twelve accessions from different locations belonging to two Selinum species, Selinum tenuifolium Wall. C. B. Clarke and Selinum vaginatum C. B. Clarke, keeping in mind their ability to identify species and establish phylogenetic relationships within and between the accessions.

RESULTS

The success rates of PCR amplification using matK and rbcL were 75.26% ± 3.65% and 57.24% ± 4.42%, and the rate of DNA sequencing was 63.84% ± 4.32% and 50.82% ± 4.36%, respectively, suggesting that success rates of species identification of the two fragments were higher than 41.00% (matK, 41.50% ± 2.81%; rbcL, 42.88% ± 2.59%), proving that these fragments might be used to identify species. The best evolutionary tree with good supporting values was produced utilizing combinations of matK + rbcL markers when phylogenetic relationships were built with random fragment combinations. The twelve accessions of Selinum collected from different locations and their molecular sequences of matK and rbcL markers were blasted with other genera of Apiaceae family, and it was found that Selinum is most closely related to Angelica species of Apiaceae family.

CONCLUSION

The present study has grouped twelve accessions of Selinum species using molecular markers into phylogenies, which is first-of-its-kind report that established interrelationships within different species of Apiaceae with respect to Selinum.

Molecular phylogeny of the Ficus virens complex (Moraceae)

The closely related species present in the subgenera of Urostigma are challenging to classify due to the existence of overlapping morphological characteristics, which makes identification habitually problematic. It is still unresolved whether the species of the Ficus virens complex, which includes F. virens, F. middletonii, F. caulocarpa, F. concinna, and F. superba, are the same or distinct species due to the complexities in classification. To clarify the circumscription between the species and re-evaluate the taxonomical status, morphological characteristics were extensively examined; further, a phylogenetic reconstruction based on two DNA markers (ITS2 and trnH-psbA) in combination with morphological traits was carried out. The phylogenetic tree constructed using the combined morphology and DNA markers revealed that the five species should be demarcated as independent species. This study supports the importance of using both molecular and morphological data for efficient discrimination of species having high similarities. Further investigation into the species present in the subgenera Urostigma may provide additional information regarding the ancestral traits and its evolutionary history.

Application of Molecular Methods in the Identification of Ingredients in Chinese Herbal Medicines

There are several kinds of Chinese herbal medicines originating from diverse sources. However, the rapid taxonomic identification of large quantities of Chinese herbal medicines is difficult using traditional methods, and the process of identification itself is prone to error. Therefore, the traditional methods of Chinese herbal medicine identification must meet higher standards of accuracy. With the rapid development of bioinformatics, methods relying on bioinformatics strategies offer advantages with respect to the speed and accuracy of the identification of Chinese herbal medicine ingredients. This article reviews the applicability and limitations of biochip and DNA barcoding technology in the identification of Chinese herbal medicines. Furthermore, the future development of the two technologies of interest is discussed.

DNA barcoding of vouchered xylarium wood specimens of nine endangered Dalbergia species

ITS2+ trnH - psbA was the best combination of DNA barcode to resolve the Dalbergia wood species studied. We demonstrate the feasibility of building a DNA barcode reference database using xylarium wood specimens. The increase in illegal logging and timber trade of CITES-listed tropical species necessitates the development of unambiguous identification methods at the species level. For these methods to be fully functional and deployable for law enforcement, they must work using wood or wood products. DNA barcoding of wood has been promoted as a promising tool for species identification; however, the main barrier to extensive application of DNA barcoding to wood is the lack of a comprehensive and reliable DNA reference library of barcodes from wood. In this study, xylarium wood specimens of nine Dalbergia species were selected from the Wood Collection of the Chinese Academy of Forestry and DNA was then extracted from them for further PCR amplification of eight potential DNA barcode sequences (ITS2, matK, trnL, trnH-psbA, trnV-trnM1, trnV-trnM2, trnC-petN, and trnS-trnG). The barcodes were tested singly and in combination for species-level discrimination ability by tree-based [neighbor-joining (NJ)] and distance-based (TaxonDNA) methods. We found that the discrimination ability of DNA barcodes in combination was higher than any single DNA marker among the Dalbergia species studied, with the best two-marker combination of ITS2+trnH-psbA analyzed with NJ trees performing the best (100% accuracy). These barcodes are relatively short regions (<350 bp) and amplification reactions were performed with high success (≥90%) using wood as the source material, a necessary factor to apply DNA barcoding to timber trade. The present results demonstrate the feasibility of using vouchered xylarium specimens to build DNA barcoding reference databases.

DNA barcoding analysis and phylogenetic relationships of tree species in tropical cloud forests

DNA barcoding is a useful tool for species identification and phylogenetic construction. But present studies have far reached a consistent result on the universality of DNA barcoding. We tested the universality of tree species DNA barcodes including rbcL, matK, trnH-psbA and ITS, and examined their abilities of species identification and phylogenetic construction in three tropical cloud forests. Results showed that the success rates of PCR amplification of rbcL, matK, trnH-psbA and ITS were 75.26% ± 3.65%, 57.24% ± 4.42%, 79.28% ± 7.08%, 50.31% ± 6.64%, and the rates of DNA sequencing were 63.84% ± 4.32%, 50.82% ± 4.36%, 72.87% ± 11.37%, 45.15% ± 8.91% respectively, suggesting that both rbcL and trnH-psbA are universal for tree species in the tropical cloud forests. The success rates of species identification of the four fragments were higher than 41.00% (rbcL: 41.50% ± 2.81%, matK: 42.88% ± 2.59%, trnH-psbA: 46.16% ± 5.11% and ITS: 47.20% ± 5.76%), demonstrating that these fragments have potentiality in species identification. When the phylogenetic relationships were built with random fragment combinations, optimal evolutionary tree with high supporting values were established using the combinations of rbcL + matK + trnH-psbA in tropical cloud forests.

DNA barcoding evaluation and implications for phylogenetic relationships in Lauraceae from China

Lauraceae are an important component of tropical and subtropical forests and have major ecological and economic significance. Owing to lack of clear-cut morphological differences between genera and species, this family is an ideal case for testing the efficacy of DNA barcoding in the identification and discrimination of species and genera. In this study, we evaluated five widely recommended plant DNA barcode loci matK, rbcL, trnH–psbA, ITS2 and the entire ITS region for 409 individuals representing 133 species, 12 genera from China. We tested the ability of DNA barcoding to distinguish species and as an alternative tool for correcting species misidentification. We also used the rbcL+matK+trnH–psbA+ITS loci to investigate the phylogenetic relationships of the species examined. Among the gene regions and their combinations, ITS was the most efficient for identifying species (57.5%) and genera (70%). DNA barcoding also had a positive role for correcting species misidentification (10.8%). Furthermore, based on the results of the phylogenetic analyses, Chinese Lauraceae species formed three supported monophyletic clades, with the Cryptocarya group strongly supported (PP = 1.00, BS = 100%) and the clade including the Persea group, Laureae and Cinnamomum also receiving strong support (PP = 1.00, BS = 98%), whereas the Caryodaphnopsis–Neocinnamomum received only moderate support (PP = 1.00 and BS = 85%). This study indicates that molecular barcoding can assist in screening difficult to identify families like Lauraceae, detecting errors of species identification, as well as helping to reconstruct phylogenetic relationships. DNA barcoding can thus help with large-scale biodiversity inventories and rare species conservation by improving accuracy, as well as reducing time and costs associated with species identification.

Replacing Sanger with Next Generation Sequencing to improve coverage and quality of reference DNA barcodes for plants

We estimate the global BOLD Systems database holds core DNA barcodes (rbcL + matK) for about 15% of land plant species and that comprehensive species coverage is still many decades away. Interim performance of the resource is compromised by variable sequence overlap and modest information content within each barcode. Our model predicts that the proportion of species-unique barcodes reduces as the database grows and that 'false' species-unique barcodes remain >5% until the database is almost complete. We conclude the current rbcL + matK barcode is unfit for purpose. Genome skimming and supplementary barcodes could improve diagnostic power but would slow new barcode acquisition. We therefore present two novel Next Generation Sequencing protocols (with freeware) capable of accurate, massively parallel de novo assembly of high quality DNA barcodes of >1400 bp. We explore how these capabilities could enhance species diagnosis in the coming decades.

Soil phosphorus heterogeneity promotes tree species diversity and phylogenetic clustering in a tropical seasonal rainforest

The niche theory predicts that environmental heterogeneity and species diversity are positively correlated in tropical forests, whereas the neutral theory suggests that stochastic processes are more important in determining species diversity. This study sought to investigate the effects of soil nutrient (nitrogen and phosphorus) heterogeneity on tree species diversity in the Xishuangbanna tropical seasonal rainforest in southwestern China. Thirty-nine plots of 400 m2 (20 × 20 m) were randomly located in the Xishuangbanna tropical seasonal rainforest. Within each plot, soil nutrient (nitrogen and phosphorus) availability and heterogeneity, tree species diversity, and community phylogenetic structure were measured. Soil phosphorus heterogeneity and tree species diversity in each plot were positively correlated, while phosphorus availability and tree species diversity were not. The trees in plots with low soil phosphorus heterogeneity were phylogenetically overdispersed, while the phylogenetic structure of trees within the plots became clustered as heterogeneity increased. Neither nitrogen availability nor its heterogeneity was correlated to tree species diversity or the phylogenetic structure of trees within the plots. The interspecific competition in the forest plots with low soil phosphorus heterogeneity could lead to an overdispersed community. However, as heterogeneity increase, more closely related species may be able to coexist together and lead to a clustered community. Our results indicate that soil phosphorus heterogeneity significantly affects tree diversity in the Xishuangbanna tropical seasonal rainforest, suggesting that deterministic processes are dominant in this tropical forest assembly.

Development of Molecular Markers for Determining Continental Origin of Wood from White Oaks (Quercus L. sect. Quercus)

To detect and avoid illegal logging of valuable tree species, identification methods for the origin of timber are necessary. We used next-generation sequencing to identify chloroplast genome regions that differentiate the origin of white oaks from the three continents; Asia, Europe, and North America. By using the chloroplast genome of Asian Q. mongolica as a reference, we identified 861 variant sites (672 single nucleotide polymorphisms (SNPs); 189 insertion/deletion (indel) polymorphism) from representative species of three continents (Q. mongolica from Asia; Q. petraea and Q. robur from Europe; Q. alba from North America), and we identified additional chloroplast polymorphisms in pools of 20 individuals each from Q. mongolica (789 variant sites) and Q. robur (346 variant sites). Genome sequences were screened for indels to develop markers that identify continental origin of oak species, and that can be easily evaluated using a variety of detection methods. We identified five indels and one SNP that reliably identify continent-of-origin, based on evaluations of up to 1078 individuals representing 13 white oak species and three continents. Due to the size of length polymorphisms revealed, this marker set can be visualized using capillary electrophoresis or high resolution gel (acrylamide or agarose) electrophoresis. With these markers, we provide the wood trading market with an instrument to comply with the U.S. and European laws that require timber companies to avoid the trade of illegally harvested timber.

Closely-related taxa influence woody species discrimination via DNA barcoding: evidence from global forest dynamics plots

To determine how well DNA barcodes from the chloroplast region perform in forest dynamics plots (FDPs) from global CTFS-ForestGEO network, we analyzed DNA barcoding sequences of 1277 plant species from a wide phylogenetic range (3 FDPs in tropics, 5 in subtropics and 5 in temperate zone) and compared the rates of species discrimination (RSD). We quantified RSD by two DNA barcode combinations (rbcL + matK and rbcL + matK + trnH-psbA) using a monophyly-based method (GARLI). We defined two indexes of closely-related taxa (Gm/Gt and S/G ratios) and correlated these ratios with RSD. The combination of rbcL + matK averagely discriminated 88.65%, 83.84% and 72.51% at the local, regional and global scales, respectively. An additional locus trnH-psbA increased RSD by 2.87%, 1.49% and 3.58% correspondingly. RSD varied along a latitudinal gradient and were negatively correlated with ratios of closely-related taxa. Successes of species discrimination generally depend on scales in global FDPs. We suggested that the combination of rbcL + matK + trnH-psbA is currently applicable for DNA barcoding-based phylogenetic studies on forest communities.