The complete plastid genome sequence of Viola selkirkii Pursh ex Goldie (Violaceae).
ABSTRACT: Viola selkirkii, belonging to the genus Viola, has heart-shaped leaves and pale purple flowers, and it is widely distributed in the Northern Hemisphere, including Europe, North America, and Asia. In this study, the plastid genome of V. selkirkii was sequenced and phylogenetic analysis was performed on 11 Viola plastid genomes. The length of the plastid genome length of V. selkirkii was 156,774 bp, and it was identified as having a typical quadripartite structure with a large single-copy region (85,930 bp), a small single-copy region (17,982 bp), and two inverted repeat regions (26,431 bp each). A phylogenetic analysis was conducted with 77 protein-coding genes from the complete plastid genomes of 11 Viola and nine Salicaceae species; the complete plastid genome of Erythroxylum novogranatense was used as an outgroup. Viola formed a monophyletic clade, and V. selkirkii was closely related to V. ulleungdoensis. These results contribute to the clear identification of the phylogenetic position of V. selkirkii in Viola.
Project description:We report the complete chloroplast genomes of four Viola species (V. mirabilis, V. phalacrocarpa, V. raddeana, and V. websteri) and the results of a comparative analysis between these species and the published plastid genome of the congeneric species V. seoulensis. The total genome length of the five Viola species, including the four species analyzed in this study and the species analyzed in the previous study, ranged from 156,507 (V. seoulensis) to 158,162 bp (V. mirabilis). The overall GC contents of the genomes were almost identical (36.2-36.3%). The five Viola plastomes each contained 111 unique genes comprising 77 protein-coding genes, 30 transfer RNA (tRNA) genes, and 4 ribosomal RNA (rRNA) genes. Among the annotated genes, 16 contained one or two introns. Based on the results of a chloroplast genome structure comparison using MAUVE, all five Viola plastomes were almost identical. Additionally, the large single copy (LSC), inverted repeat (IR), and small single copy (SSC) junction regions were conserved among the Viola species. A total of 259 exon, intron, and intergenic spacer (IGS) fragments were compared to verify the divergence hotspot regions. The nucleotide diversity (Pi) values ranged from 0 to 0.7544. The IR region was relatively more conserved than the LSC and SSC regions. The Pi values in ten noncoding regions were relatively high (>0.03). Among these regions, all but rps19-trnH, petG-trnW, rpl16-rps3, and rpl2-rpl23 represent useful molecular markers for phylogenetic studies and will be helpful to resolve the phylogenetic relationships of Viola. The phylogenetic tree, which used 76 protein-coding genes from 21 Malpighiales species and one outgroup species (Averrhoa carambola), revealed that Malpighiales is divided into five clades at the family level: Erythroxylaceae, Chrysobalanaceae, Euphorbiaceae, Salicaceae, and Violaceae. Additionally, Violaceae was monophyletic, with a bootstrap value of 100% and was divided into two subclades.
Project description:<i>Viola verecunda</i> is a perennial plant native to the mountainous areas of Northeast Asia. Here the complete chloroplast genome of <i>V. verecunda</i> and its phylogenetic relationships to other species within the genus <i>Viola</i> are reported. The complete chloroplast genome of <i>V. verecunda</i> is 157,843 bp in length and circular in structure with four regions: a large single-copy region (86,345 bp), a small single-copy region (17,292 bp), and a pair of inverted repeat regions (27,103 bp each). The chloroplast genome contains 111 unique genes comprising 77 protein-coding, 30 unique tRNA, and 4 unique rRNA genes. Based on the protein-coding gene sequences from eight <i>Viola</i> chloroplast genomes, with <i>Balanops balansae</i> designated as the outgroup, maximum likelihood tree analysis indicates that <i>V. verecunda</i> is more closely related to <i>V. raddeana</i> than to other <i>Viola</i> species. The complete chloroplast genome of <i>V. verecunda</i> contributes to a better understanding of the phylogenetic relationships among <i>Viola</i> species.
Project description:<i>Viola philippica</i>, as a traditional Chinese medicine, has great value in treating various diseases. Here, we report the chloroplast genome of <i>V. philippica</i> and its phylogenetic feature. The complete chloroplast genome is 156,744 bp in length, assembled from 22,346,570 reads, and its GC contents ratio is 36.26%. Its long single-copy (LSC) region is 85,892 bp. The small single-copy (SSC) region covers 18,006 bp and inverted repeat (IR) is 26,423 bp. It encodes 77 genes, including 43 protein genes, 4 rRNA genes, and 30 tRNA genes. Moreover, according to the phylogenetic analysis for a total of 12 chloroplast sequences, <i>V. philippica</i> demonstrated close relationship within genus <i>Viola</i>.
Project description:<i>Viola prionantha</i> belongs to the family Violaceae. It has been widely used for a traditional Chinese herb in China. We determined the complete chloroplast genome sequence of <i>V. prionantha</i>. The whole chloroplast genome was 156,501 bp in length, consisting of a pair of inverted repeats (IR) of 26,404 bp, each, a large single-copy (LSC) region of 85,689 bp, and a small single-copy (SSC) region of 18,004 bp. We annotated 131 genes, including 84 coding sequences, 8 rRNA sequences, 37 tRNA sequences, and 2 pesudogenes. Among the annotated genes Phylogenetic analysis revealed that <i>V. prionantha</i> and <i>Viola seoulensis</i> clustered together as sisters.
Project description:<i>Viola Prionantha</i> belongs to the family Violaceae. It has been widely used for a traditional Chinese herb with antibacterial activity and is grown as an early spring ornamental species in China. In this study, we determined the complete chloroplast genome sequence of <i>V. prionantha</i> which forms a circular structure. The whole chloroplast genome was 156,501 bp in length, consisting of a pair of inverted repeats (IR) of 26,404 bp, a large single-copy (LSC) region of 85,689 bp, and a small single-copy (SSC) region of 18,004 bp. We annotated 131 genes, including 84 coding sequences, 8 rRNA sequences, 37 tRNA sequences and 2 pesudogenes. Among the annotated genes, 17 genes contained one or two introns. Furthermore, a phylogenetic analysis revealed that <i>V. prionantha</i> and <i>V. seoulensis</i> clustered together as sisters to other Violaceae species.
Project description:Functional gene transfer from organelles to the nucleus, known as intracellular gene transfer (IGT), is an ongoing process in flowering plants. The complete plastid genomes (plastomes) of two Ulleung island endemic violets, <i>Viola ulleungdoensis</i> and <i>V. woosanensis</i>, were characterized, revealing a lack of the plastid-encoded <i>infA</i>, <i>rpl32</i>, and <i>rps16</i> genes. In addition, functional replacement of the three plastid-encoded genes in the nucleus was confirmed within the genus <i>Viola</i> and the order Malpighiales. Three strategies for the acquisition of a novel transit peptide for successful IGT were identified in the genus <i>Viola</i>. Nuclear <i>INFA</i> acquired a novel transit peptide with very low identity between these proteins, whereas the nuclear <i>RPL32</i> gene acquired an existing transit peptide <i>via</i> fusion with the nuclear-encoded plastid-targeted <i>SOD</i> gene (Cu-Zn superoxide dismutase superfamily) as one exon, and translated both proteins in the cytosol using alternative mRNA splicing. Nuclear <i>RPS16</i> contains an internal transit peptide without an N-terminal extension. Gene loss or pseudogenization of the plastid-borne <i>rpl32</i> and <i>rps16</i> loci was inferred to occur in the common ancestor of the genus <i>Viola</i> based on an infrageneric phylogenetic framework in Korea. Although <i>infA</i> was lost in the common ancestor of the order Malpighiales, the <i>rpl32</i> and <i>rps16</i> genes were lost multiple times independently within the order. Our current study sheds additional light on plastid genome composition and IGT mechanisms in the violet genus and in the order Malpighiales.
Project description:Allopolyploidization accounts for a significant fraction of speciation events in many eukaryotic lineages. However, existing phylogenetic and dating methods require tree-like topologies and are unable to handle the network-like phylogenetic relationships of lineages containing allopolyploids. No explicit framework has so far been established for evaluating competing network topologies, and few attempts have been made to date phylogenetic networks. We used a four-step approach to generate a dated polyploid species network for the cosmopolitan angiosperm genus Viola L. (Violaceae Batch.). The genus contains ca 600 species and both recent (neo-) and more ancient (meso-) polyploid lineages distributed over 16 sections. First, we obtained DNA sequences of three low-copy nuclear genes and one chloroplast region, from 42 species representing all 16 sections. Second, we obtained fossil-calibrated chronograms for each nuclear gene marker. Third, we determined the most parsimonious multilabeled genome tree and its corresponding network, resolved at the section (not the species) level. Reconstructing the "correct" network for a set of polyploids depends on recovering all homoeologs, i.e., all subgenomes, in these polyploids. Assuming the presence of Viola subgenome lineages that were not detected by the nuclear gene phylogenies ("ghost subgenome lineages") significantly reduced the number of inferred polyploidization events. We identified the most parsimonious network topology from a set of five competing scenarios differing in the interpretation of homoeolog extinctions and lineage sorting, based on (i) fewest possible ghost subgenome lineages, (ii) fewest possible polyploidization events, and (iii) least possible deviation from expected ploidy as inferred from available chromosome counts of the involved polyploid taxa. Finally, we estimated the homoploid and polyploid speciation times of the most parsimonious network. Homoploid speciation times were estimated by coalescent analysis of gene tree node ages. Polyploid speciation times were estimated by comparing branch lengths and speciation rates of lineages with and without ploidy shifts. Our analyses recognize Viola as an old genus (crown age 31?Ma) whose evolutionary history has been profoundly affected by allopolyploidy. Between 16 and 21 allopolyploidizations are necessary to explain the diversification of the 16 major lineages (sections) of Viola, suggesting that allopolyploidy has accounted for a high percentage-between 67% and 88%-of the speciation events at this level. The theoretical and methodological approaches presented here for (i) constructing networks and (ii) dating speciation events within a network, have general applicability for phylogenetic studies of groups where allopolyploidization has occurred. They make explicit use of a hitherto underexplored source of ploidy information from chromosome counts to help resolve phylogenetic cases where incomplete sequence data hampers network inference. Importantly, the coalescent-based method used herein circumvents the assumption of tree-like evolution required by most techniques for dating speciation events.
Project description:BACKGROUND: DNA-dependent RNA polymerase IV and V (Pol IV and V) are multi-subunit enzymes occurring in plants. The origin of Pol V, specific to angiosperms, from Pol IV, which is present in all land plants, is linked to the duplication of the gene encoding the largest subunit and the subsequent subneofunctionalization of the two paralogs (NRPD1 and NRPE1). Additional duplication of the second-largest subunit, NRPD2/NRPE2, has happened independently in at least some eudicot lineages, but its paralogs are often subject to concerted evolution and gene death and little is known about their evolution nor their affinity with Pol IV and Pol V. RESULTS: We sequenced a approximately 1500 bp NRPD2/E2-like fragment from 18 Viola species, mostly paleopolyploids, and 6 non-Viola Violaceae species. Incongruence between the NRPD2/E2-like gene phylogeny and species phylogeny indicates a first duplication of NRPD2 relatively basally in Violaceae, with subsequent sorting of paralogs in the descendants, followed by a second duplication in the common ancestor of Viola and Allexis. In Viola, the mutation pattern suggested (sub-) neofunctionalization of the two NRPD2/E2-like paralogs, NRPD2/E2-a and NRPD2/E2-b. The dN/dS ratios indicated that a 54 bp region exerted strong positive selection for both paralogs immediately following duplication. This 54 bp region encodes a domain that is involved in the binding of the Nrpd2 subunit with other Pol IV/V subunits, and may be important for correct recognition of subunits specific to Pol IV and Pol V. Across all Viola taxa 73 NRPD2/E2-like sequences were obtained, of which 23 (32%) were putative pseudogenes - all occurring in polyploids. The NRPD2 duplication was conserved in all lineages except the diploid MELVIO clade, in which NRPD2/E2-b was lost, and its allopolyploid derivates from hybridization with the CHAM clade, section Viola and section Melanium, in which NRPD2/E2-a occurred in multiple copies while NRPD2/E2-b paralogs were either absent or pseudogenized. CONCLUSIONS: Following the relatively recent split of Pol IV and Pol V, our data indicate that these two multi-subunit enzymes are still in the process of specialization and each acquiring fully subfunctionalized copies of their subunit genes. Even after specialization, the NRPD2/E2-like paralogs are prone to pseudogenization and gene conversion and NRPD2 and NRPE2 copy number is a highly dynamic process modulated by allopolyploidy and gene death.
Project description:The phylogenies of allopolyploids take the shape of networks and cannot be adequately represented as bifurcating trees. Especially for high polyploids (i.e., organisms with more than six sets of nuclear chromosomes), the signatures of gene homoeolog loss, deep coalescence, and polyploidy may become confounded, with the result that gene trees may be congruent with more than one species network. Herein, we obtained the most parsimonious species network by objective comparison of competing scenarios involving polyploidization and homoeolog loss in a high-polyploid lineage of violets (Viola, Violaceae) mostly or entirely restricted to North America, Central America, or Hawaii. We amplified homoeologs of the low-copy nuclear gene, glucose-6-phosphate isomerase (GPI), by single-molecule polymerase chain reaction (PCR) and the chloroplast trnL-F region by conventional PCR for 51 species and subspecies. Topological incongruence among GPI homoeolog subclades, owing to deep coalescence and two instances of putative loss (or lack of detection) of homoeologs, were reconciled by applying the maximum tree topology for each subclade. The most parsimonious species network and the fossil-based calibration of the homoeolog tree favored monophyly of the high polyploids, which has resulted from allodecaploidization 9-14 Ma, involving sympatric ancestors from the extant Viola sections Chamaemelanium (diploid), Plagiostigma (paleotetraploid), and Viola (paleotetraploid). Although two of the high-polyploid lineages (Boreali-Americanae, Pedatae) remained decaploid, recurrent polyploidization with tetraploids of section Plagiostigma within the last 5 Ma has resulted in two 14-ploid lineages (Mexicanae, Nosphinium) and one 18-ploid lineage (Langsdorffianae). This implies a more complex phylogenetic and biogeographic origin of the Hawaiian violets (Nosphinium) than that previously inferred from rDNA data and illustrates the necessity of considering polyploidy in phylogenetic and biogeographic reconstruction.
Project description:The Hawaiian endemic Viola kauaensis A. Gray has a broad distribution in bogs of Kaua`i and a limited distribution on mesic ridges in the Ko`olau Mountains of O`ahu. Based on differences in scale, the O`ahu populations of Viola kauaensis had previously been described as a distinct taxon. The taxonomic status of the O`ahu populations was reevaluated through a morphometric analysis of all varieties of Viola kauaensis and the morphologically similar Viola vanroyenii. Morphological features of historic and freshly collected specimens of all varieties of Viola kauaensis were analyzed with a principal components analysis. Populations from O`ahu represent a distinct cluster that slightly overlaps with Viola kauaensis var. kauaensis. Lamina width, apex angle, and base angles contribute to the separation of the O`ahu populations from other varieties of Viola kauaensis. Due to differences in scale, the O`ahu populations are described as Viola kauaensis var. hosakae, a new critically endangered taxon.