Research Article |
Corresponding author: Yu-Min Shui ( ymshui@mail.kib.ac.cn ) Academic editor: Fang Wen
© 2020 Wen-Hong Chen, Ya-Mei Zhang, Shi-Wei Guo, Zhi-Rong Zhang, Li Chen, Yu-Min Shui.
This is an open access article distributed under the terms of the Creative Commons Attribution License (CC BY 4.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited.
Citation:
Chen W-H, Zhang Y-M, Guo S-W, Zhang Z-R, Chen L, Shui Y-M (2020) Reassessment of Bournea Oliver (Gesneriaceae) based on molecular and palynological evidence. In: Shui Y-M, Chen W-H, Ren M-X, Wen F, Hong X, Qiu Z-J, Wei Y-G, Kang M (Eds) Taxonomy of Gesneriaceae in China and Vietnam. PhytoKeys 157: 27-41. https://doi.org/10.3897/phytokeys.157.55254
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The former genus Bournea is endemic to China, including two species, has been under consideration for incorporation into the expanded genus Oreocharis s.l. in Gesneriaceae. The phylogenetic tree inferred from two DNA sequences (trnL-F and ITS) showed that this genus is deeply nested into Oreocharis s.l. However, the new tree from seven ones (atpB-rbcL, ndhH-rps15-ycf1, rpl132, trnC-trnD, trnL-F, trnT-trnL of chloroplast DNA and ITS regions) revealed that Bournea is the sister group of other of Oreocharis s.l. Furthermore, Bournea is morphologically different from other Oreocharis based on existing data. We suggest keeping Bournea as an independent genus in Gesneriaceae.
Bournea, morphological characters of flowers, Oreocharis, phylogeny, pollen grains
The genus Bournea Oliver was established in 1893 based on the type species Bournea sinensis Oliv., which was endemic to Guangdong province, Southeast China (
The morphology of Bournea sinensis Oliv. (A–E) and B. leiophylla (W. T. Wang) W. T. Wang (F–J). A plant B inflorescence C calyx and disc D stigma E front view of corolla showing the anthers and the style and stamens F plant G inflorescence H pistil and disc I stigma J front view of corolla showing the anthers.
The preliminary phylogenetic analysis revealed that Bournea ought to be combined into the expanded genus Oreocharis s.l. in Gesneriaceae.
Our recent study based on six chloroplast sequences has revealed a more well-resolved relationship of Bournea with the expanded genus. In fact, the low resolution from the above two DNA regions within the expanded Oreocharis s.l. has been troubling us. Here, we adopted more DNA sequences to explore the precise phylogenetic position of the former Bournea within the expanded genus to reassess the necessity of the taxonomic combination made by
Molecular materials. First, we sampled 52 samples of 46 species in the expanded Oreocharis and two outgroup taxa (Suppl. material
DNA extraction and sequence assembly of the complete cp DNA. Total genomic DNA of Oreocharis using a modified CTAB (
Abstract of the cp DNA markers and matric preparation. First, we produced individual gene trees of the six cp DNA markers and ITS. Then, we compared the similarity of these gene trees and further decided which sequences can be combined or not. Next, we compared the different combinations of cp DNA markers and ITS. We confirmed that five sequences atpB-rbcL, ndhH-rps15-ycf1, rpl132, trnL-F, trnT-trnL, and ITS seem to provide strong support to resolve the relationship of Bournea within the expanded Oreocharis. Furthermore, six cp DNA markers with additional cp DNA marker trnC-trnD can provide more robust support than the above five cp DNA markers. The above sequences were abstracted separately under the Geneious v10.2.3 (
Methods of phylogenetic analysis. The best-fitting models (GTR) of molecular evolution for Bayes inference (BI) and the model of the Maximum Likelihood (ML) were determined by the Akaike Information Criterion (AIC) in MrModelTest within MrMTgui (https://www.softpedia.com/get/Science-CAD/MrMTgui.shtml). Bayes Inference (BI) analyses were conducted with MrBayes v3.2.3 on Windows 7 (
The methods on SEM for pollen grains followed
Six plastid markers are enough to resolve the relationship of Bournea within Oreocheris s.l. The expanded genus Oreocharis s.l. can be divided into two clades in Bayes tree (100% posterior probability value, PPV=100%) and Raxmil tree (92% bootstrap value, BTV=92%) based on the six cp DNA markers (atpB-rbcL, ndhH-rps15-ycf1, rpl132, trnC-trnD, trnL-F, trnT-trnL) (Fig.
The Bayes inference (BI) and Maximum likelihood (ML) tree inferred from six cp DNA markers (atpB-rbcL, ndhH-rps15-ycf1, rpl132, trnC-trnD, trnL-F, trnT-trnL) of the expanded genus Oreocharis s.l. in Gesneriaceae. Note 1) the red clade indicates the position of Bournea in phylogenetic trees; 2) the number of the node respectively indicates posterior probability values in BI and bootstrap values in ML, ※ indicates < 50%.
Six plastid markers together with one nuclear marker (ITS) are enough to resolve the relationship of Bournea within Oreocharis s.l. Within the combined analysis of six plastid markers (atpB-rbcL, ndhH-rps15-ycf1, rpl132, trnC-trnD, trnL-F, trnT-trnL) and one nuclear marker (ITS), all the two species in Bournea form a monophyletic group, and the genus Bournea becomes a sister clade to the other Oreocharis s.l. (Fig.
However, five plastid markers and its combination with one nuclear marker (ITS) cannot completely resolve the relationship of Bournea within Oreocheris s.l. As to five cp DNA markers (atpB-rbcL, ndhH-rps15-ycf1, rpl132, trnL-F, trnT-trnL), the relationship of Bournea seems to be resolved (PPV=100, BSV=100). As to the combination of 5 cp DNA markers and ITS, the relationship of Bournea is not completely resolved (PPV=100%, BSV=65%). At the above second clade sister to the Bournea clade, the groups have been resolved with weak support (BSV<50%). Nevertheless, the yellow-flowered group and the former genus Thamnocharis with now Oreocharis espuirolii show the same case as the above phylogenetic result inferred from the above more markers (Figs
The Bayes inference (BI) and Maximum likelihood (ML) tree inferred from six cp DNA markers (atpB-rbcL, ndhH-rps15-ycf1, rpl132, trnC-trnD, trnL-F, trnT-trnL) and ITS of the expanded genus Oreocharis s.l. in Gesneriaceae. Note 1) the red clade indicates the position of Bournea in phylogenetic trees; 2) the number of the node respectively indicates posterior probability values in BI and bootstrap values in ML, ※ indicates < 50%.
The two species in the genus show almost the same characteristics. In the two species, the pollen grains single-grained, isopolar, radial symmetry, prolate, amb circular, tricolporate, aperture membrane granulum, exine verrucate, tectum verrucate, supratectal elements granulum (Fig.
The morphology of pollen grains of Bournea sinensis Oliv. (A–D) and B. leiophylla (W. T. Wang) W. T. Wang (E–H) by SEM. A polar view showing pollen grain with three equatorial, colporus apertures B equatorial view showing single free, prolate pollen grain C equatorial view show apertures and granular aperture membrane D detail showing verrucate tectum with granular E polar view showing pollen grain with three equatorial, colporus apertures F equatorial view showing single free, oblate pollen grain G equatorial view show apertures and granular aperture membrane H detail showing verrucate tectum with granular.
The phylogenetic position of Bournea inferred from chloroplast genes seems to be more convincing than those from the combination of chloroplast and nuclear gene (ITS). The relationship of Bournea has been completely resolved by the phylogenetic tree inferred from six cp DNA markers (Fig.
It is pending that floral actinomorphy can be considered as one of the diagnostic characteristics between Bournea and Thamnocharis within Oreocharis s.l. In the expanded genus, both of the two species of Bournea are morphologically very similar to the monotypic genus Thamnocharis Burtt in actinomorphic corolla (
More chloroplast markers provide useful data to resolve the phylogenetic relationship within the expanded genus Oreocharis s.l. The two DNA markers (trnL-F and ITS) cannot resolve any above relationship (
The verrucate exine of pollen grains can differentiate the former Bournea from other of the Oreocharis s.l. The case seems to match the above relationship inferred from the more chloroplast markers. At present, Bournea can be diagnosed by the verrucate exine of pollen grains within the expanded genus. However, only one more than 40% (50 out of 130) species of the expanded genus have been sampled to explore their pollen grains in the expanded genus. It is pending if the unique characteristics of the pollen grains happen to some un-sampled species. So, more palynological evidence may be necessary to the taxonomic treatment within the expanded genus.
We gratefully acknowledge Dr. Liang Zhang of the Kunming Institute of Botany, Chinese Academy of Sciences, and Dr. Michael Möller of Royal Botanic Gardens, Edinburgh, for providing constructive suggestions regarding the analysis and contents. We thank Prof, Wen-Bo Liao and Dr. Qiang Fan of Sun Yat-sen University, and Mr. Jian-Qin Wu of Tian-Bao-Yan National Nature Reserve in Fujian Province for providing help in surveys. Dr. Ming Kang and Dr. Li-Hua Yang provided some molecular sequences for our phylogenetic analysis. We would also like to thank Stephen Maciejewski, The Gesneriad Society, and Michael LoFurno, Adjunct Professor, Temple University, Philadelphia PA, USA, for their editorial assistance. This work was supported by the National Natural Science Foundation of China (Grant no. 31470306, 31000258).
Tables S1, S2
Data type: dataset
Explanation note: Table S1. Sample list of the species and their ITS sequences in the expanded genus Oreocharis in Gesneriaceae. Table S2. Sample list of the species and their chloroplast sequences in the expanded genus Oreocharis in Gesneriaceae..
Figure S1
Data type: phylogenetic tree
Explanation note: The Bayes inference (BI) and Maximum likelihood (ML) tree inferred from 5 cp DNA markers (atpB-rbcL, ndhH-rps15-ycf1, rpl132, trnL-F, trnT-trnL) of the expanded genus Oreocharis s.l. in Gesneriaceae. Note 1) the red clade indicates the position of Bournea in phylogenetic trees; 2) the number of the node respectively indicates posterior probability values in BI and bootstrap values in ML, ※ indicates < 50%.
Figure S2
Data type: phylogenetic tree
Explanation note: The Bayes inference (BI) and Maximum likelihood (ML) tree inferred from 5 cp DNA markers (atpB-rbcL, ndhH-rps15-ycf1, rpl132, trnL-F, trnT-trnL) and ITS of the expanded genus Oreocharis s.l. in Gesneriaceae. Note 1) the red clade indicates the position of Bournea in phylogenetic trees; 2) the number of the node respectively indicates posterior probability values in BI and bootstrap values in ML, ※ indicates < 50%..
Supporting materials
Data type: phylogenetic
Explanation note: Data 1 DNA sequences of 6 cp genes + ITS from 52 samples and 48 species of Oreocharis in Gesneriaceae. https://figshare.com/s/23027089ad5af90fc3b3
Data 2 DNA sequences of 6 cp genes from 52 samples and 48 species of Oreocharis in Gesneriaceae. https://figshare.com/s/455c93000b474faee7d2
Data 3 DNA sequences of 5 cp genes + ITS from 52 samples and 48 species of Oreocharis in Gesneriaceae. https://figshare.com/s/3a8fe0f8923ccc120c68
Data 4 DNA sequences of 5 cp genes from 52 samples and 48 species of Oreocharis in Gesneriaceae. https://figshare.com/s/76c56fd0ff6fcaa26485
Data 5 DNA sequences of ITS-from 52 samples and 48 species of Oreocharis in Gesneriaceae. https://figshare.com/s/8c045c93b02389fd6777
Data 6 DNA sequences of atpB-rbcL from 52 samples and 48 species of Oreocharis in Gesneriaceae. https://figshare.com/s/b177b05cbcc08d22d9c3
Data 7 DNA sequences of rpl132 from 52 samples and 48 species of Oreocharis in Gesneriaceae. https://figshare.com/s/a2930a767a1411dc49c2
Data 8 DNA sequences of ndhH-rps15-ycf1 from 52 samples and 48 species of Oreocharis in Gesneriaceae. https://figshare.com/s/8ed14b5f7de0552107cc
Data 9 DNA sequences of trnC-trnD from 52 samples and 48 species of Oreocharis in Gesneriaceae. https://figshare.com/s/93609c5db11bc52b7d80
Data 10 DNA sequences of trnL-F from 52 samples and 48 species of Oreocharis in Gesneriaceae. https://figshare.com/s/ee47f235d59d00f3e89a
Data 11 DNA sequences of trnT-trnL from 52 samples and 48 species of Oreocharis in Gesneriaceae. https://figshare.com/s/b55363c06cfd1235e435.