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Comparative analysis of a large dataset indicates that internal transcribed spacer (ITS) should be incorporated into the core barcode for seed plants.

ABSTRACT: A two-marker combination of plastid rbcL and matK has previously been recommended as the core plant barcode, to be supplemented with additional markers such as plastid trnH-psbA and nuclear ribosomal internal transcribed spacer (ITS). To assess the effectiveness and universality of these barcode markers in seed plants, we sampled 6,286 individuals representing 1,757 species in 141 genera of 75 families (42 orders) by using four different methods of data analysis. These analyses indicate that (i) the three plastid markers showed high levels of universality (87.1-92.7%), whereas ITS performed relatively well (79%) in angiosperms but not so well in gymnosperms; (ii) in taxonomic groups for which direct sequencing of the marker is possible, ITS showed the highest discriminatory power of the four markers, and a combination of ITS and any plastid DNA marker was able to discriminate 69.9-79.1% of species, compared with only 49.7% with rbcL + matK; and (iii) where multiple individuals of a single species were tested, ascriptions based on ITS and plastid DNA barcodes were incongruent in some samples for 45.2% of the sampled genera (for genera with more than one species sampled). This finding highlights the importance of both sampling multiple individuals and using markers with different modes of inheritance. In cases where it is difficult to amplify and directly sequence ITS in its entirety, just using ITS2 is a useful backup because it is easier to amplify and sequence this subset of the marker. We therefore propose that ITS/ITS2 should be incorporated into the core barcode for seed plants.

SUBMITTER: China Plant BOL Group

PROVIDER: S-EPMC3241788 | biostudies-literature | 2011 Dec

REPOSITORIES: biostudies-literature

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Comparative analysis of a large dataset indicates that internal transcribed spacer (ITS) should be incorporated into the core barcode for seed plants.

Li De-Zhu DZ Gao Lian-Ming LM Li Hong-Tao HT Wang Hong H Ge Xue-Jun XJ Liu Jian-Quan JQ Chen Zhi-Duan ZD Zhou Shi-Liang SL Chen Shi-Lin SL Yang Jun-Bo JB Fu Cheng-Xin CX Zeng Chun-Xia CX Yan Hai-Fei HF Zhu Ying-Jie YJ Sun Yong-Shuai YS Chen Si-Yun SY Zhao Lei L Wang Kun K Yang Tuo T Duan Guang-Wen GW

Proceedings of the National Academy of Sciences of the United States of America 20111118 49

A two-marker combination of plastid rbcL and matK has previously been recommended as the core plant barcode, to be supplemented with additional markers such as plastid trnH-psbA and nuclear ribosomal internal transcribed spacer (ITS). To assess the effectiveness and universality of these barcode markers in seed plants, we sampled 6,286 individuals representing 1,757 species in 141 genera of 75 families (42 orders) by using four different methods of data analysis. These analyses indicate that (i) ...[more]

PMID: 22100737

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Project description:BackgroundDNA barcoding offers an efficient way to determine species identification and to measure biodiversity. For dinoflagellates, an ancient alveolate group of about 2000 described extant species, DNA barcoding studies have revealed large amounts of unrecognized species diversity, most of which is not represented in culture collections. To date, two mitochondrial gene markers, Cytochrome Oxidase I (COI) and Cytochrome b oxidase (COB), have been used to assess DNA barcoding in dinoflagellates, and both failed to amplify all taxa and suffered from low resolution. Nevertheless, both genes yielded many examples of morphospecies showing cryptic speciation and morphologically distinct named species being genetically similar, highlighting the need for a common marker. For example, a large number of cultured Symbiodinium strains have neither taxonomic identification, nor a common measure of diversity that can be used to compare this genus to other dinoflagellates.Methodology/principal findingsThe purpose of this study was to evaluate the Internal Transcribed Spacer units 1 and 2 (ITS) of the rDNA operon, as a high resolution marker for distinguishing species dinoflagellates in culture. In our study, from 78 different species, the ITS barcode clearly differentiated species from genera and could identify 96% of strains to a known species or sub-genus grouping. 8.3% showed evidence of being cryptic species. A quarter of strains identified had no previous species identification. The greatest levels of hidden biodiversity came from Scrippsiella and the Pfiesteriaceae family, whilst Heterocapsa strains showed a high level of mismatch to their given species name.Conclusions/significanceThe ITS marker was successful in confirming species, revealing hidden diversity in culture collections. This marker, however, may have limited use for environmental barcoding due to paralogues, the potential for unidentifiable chimaeras and priming across taxa. In these cases ITS would serve well in combination with other markers or for specific taxon studies.

Project description:Molecular-based taxonomy, specifically DNA barcoding, has streamlined organism identification. For land plants, the recommended 2-locus barcode of rbcL and matK is not suitable for all groups, thus the second subunit of the nuclear internal transcribed spacer (ITS2) has received attention as a possible alternative. To date, evaluations of ITS2 have mostly been limited in scope to specific plant orders/families and single source material. Prior to using ITS2 to routinely characterize land plants present in environmental samples (i.e., DNA metabarcoding), a wet lab protocol optimized for bulk sample types is needed. To address this gap, in this study we determined the broad recoverability across land plants when using published ITS2 primer pairs, and subsequently optimized the PCR reaction constituents and cycling conditions for the best two performing primer pairs (ITS2F/ITSp4 and ITSp3/ITSu4). Using these conditions, both primer pairs were used to characterize land plants present in 17 diverse soils collected from across the US. The resulting PCR amplicons were prepared into libraries and pooled for sequencing on an Illumina® MiniSeq. Our existing bioinformatics workflow was used to process raw sequencing data and taxonomically assign unique ITS2 plant sequences by comparison to GenBank. Given strict quality criteria were imposed on sequences for inclusion in data analysis, only 43.6% and 7.5% of sequences from ITS2F/ITSp4 and ITSp3/ITSu4 respectively remained for taxonomic comparisons; ~7-11% of sequences originated from fungal co-amplification. The number of orders and families recovered did differ between primer pairs, with ITS2F/ITSp4 consistently outperforming ITSp3/ITSu4 by >15%. Primer pair bias was observed in the recovery of certain taxonomic groups; ITS2F/ITSp4 preferentially recovered flowering plants and grasses, whereas ITSp3/ITSu4 recovered more moss taxa. To maximize data recovery and reduce potential bias, we advocate that studies using ITS2 to characterize land plants from environmental samples such as soil use a multiple primer pair approach.

Dataset Information

Comparative analysis of a large dataset indicates that internal transcribed spacer (ITS) should be incorporated into the core barcode for seed plants.

Publications

Comparative analysis of a large dataset indicates that internal transcribed spacer (ITS) should be incorporated into the core barcode for seed plants.

Similar Datasets

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