Dataset Information

Taxonomic scheme of the order Chaetophorales (Chlorophyceae, Chlorophyta) based on chloroplast genomes.

ABSTRACT: BACKGROUND:Order Chaetophorales currently includes six families, namely Schizomeridaceae, Aphanochaetaceae, Barrancaceae, Uronemataceae, Fritschiellaceae, and Chaetophoraceae. The phylogenetic relationships of Chaetophorales have been inferred primarily based on short and less informative rDNA sequences. This study aimed to phylogenetically reconstruct order Chaetophorales and determine the taxonomic scheme, and to further understand the evolution of order Chaetophorales. RESULTS:In the present study, seven complete and five fragmentary chloroplast genomes were harvested. Phylogenomic and comparative genomic analysis were performed to determine the taxonomic scheme within Chaetophorales. Consequently, Oedogoniales was found to be a sister to a clade linking Chaetophorales and Chaetopeltidales. Schizomeriaceae, and Aphanochaetaceae clustered into a well-resolved basal clade in Chaetophorales, inconsistent with the results of phylogenetic analysis based on rDNA sequences. Comparative genomic analyses revealed that the chloroplast genomes of Schizomeriaceae and Aphanochaetaceae were highly conserved and homologous, highlighting the closest relationship in this order. Germination types of zoospores precisely correlated with the phylogenetic relationships. CONCLUSIONS:chloroplast genome structure analyses, synteny analyses, and zoospore germination analyses were concurrent with phylogenetic analyses based on the chloroplast genome, and all of them robustly determined the unique taxonomic scheme of Chaetophorales and the relationships of Oedogoniales, Chaetophorales, and Chaetopeltidales.

SUBMITTER: Liu B

PROVIDER: S-EPMC7320567 | biostudies-literature | 2020 Jun

REPOSITORIES: biostudies-literature

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Taxonomic scheme of the order Chaetophorales (Chlorophyceae, Chlorophyta) based on chloroplast genomes.

Liu Benwen B Hu Yuxin Y Hu Zhengyu Z Liu Guoxiang G Zhu Huan H

BMC genomics 20200626 1

<h4>Background</h4>Order Chaetophorales currently includes six families, namely Schizomeridaceae, Aphanochaetaceae, Barrancaceae, Uronemataceae, Fritschiellaceae, and Chaetophoraceae. The phylogenetic relationships of Chaetophorales have been inferred primarily based on short and less informative rDNA sequences. This study aimed to phylogenetically reconstruct order Chaetophorales and determine the taxonomic scheme, and to further understand the evolution of order Chaetophorales.<h4>Results</h4> ...[more]

PMID: 32590931

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Project description:BackgroundTo gain insight into the branching order of the five main lineages currently recognized in the green algal class Chlorophyceae and to expand our understanding of chloroplast genome evolution, we have undertaken the sequencing of chloroplast DNA (cpDNA) from representative taxa. The complete cpDNA sequences previously reported for Chlamydomonas (Chlamydomonadales), Scenedesmus (Sphaeropleales), and Stigeoclonium (Chaetophorales) revealed tremendous variability in their architecture, the retention of only few ancestral gene clusters, and derived clusters shared by Chlamydomonas and Scenedesmus. Unexpectedly, our recent phylogenies inferred from these cpDNAs and the partial sequences of three other chlorophycean cpDNAs disclosed two major clades, one uniting the Chlamydomonadales and Sphaeropleales (CS clade) and the other uniting the Oedogoniales, Chaetophorales and Chaetopeltidales (OCC clade). Although molecular signatures provided strong support for this dichotomy and for the branching of the Oedogoniales as the earliest-diverging lineage of the OCC clade, more data are required to validate these phylogenies. We describe here the complete cpDNA sequence of Oedogonium cardiacum (Oedogoniales).ResultsLike its three chlorophycean homologues, the 196,547-bp Oedogonium chloroplast genome displays a distinctive architecture. This genome is one of the most compact among photosynthetic chlorophytes. It has an atypical quadripartite structure, is intron-rich (17 group I and 4 group II introns), and displays 99 different conserved genes and four long open reading frames (ORFs), three of which are clustered in the spacious inverted repeat of 35,493 bp. Intriguingly, two of these ORFs (int and dpoB) revealed high similarities to genes not usually found in cpDNA. At the gene content and gene order levels, the Oedogonium genome most closely resembles its Stigeoclonium counterpart. Characters shared by these chlorophyceans but missing in members of the CS clade include the retention of psaM, rpl32 and trnL(caa), the loss of petA, the disruption of three ancestral clusters and the presence of five derived gene clusters.ConclusionThe Oedogonium chloroplast genome disclosed additional characters that bolster the evidence for a close alliance between the Oedogoniales and Chaetophorales. Our unprecedented finding of int and dpoB in this cpDNA provides a clear example that novel genes were acquired by the chloroplast genome through horizontal transfers, possibly from a mitochondrial genome donor.

Project description:BackgroundSpecies of Bryopsidales form ecologically important components of seaweed communities worldwide. These siphonous macroalgae are composed of a single giant tubular cell containing millions of nuclei and chloroplasts, and harbor diverse bacterial communities. Little is known about the diversity of chloroplast genomes (cpDNAs) in this group, and about the possible consequences of intracellular bacteria on genome composition of the host. We present the complete cpDNAs of Bryopsis plumosa and Tydemania expeditiones, as well as a re-annotated cpDNA of B. hypnoides, which was shown to contain a higher number of genes than originally published. Chloroplast genomic data were also used to evaluate phylogenetic hypotheses in the Chlorophyta, such as monophyly of the Ulvophyceae (the class in which the order Bryopsidales is currently classified).ResultsBoth DNAs are circular and lack a large inverted repeat. The cpDNA of B. plumosa is 106,859 bp long and contains 115 unique genes. A 13 kb region was identified with several freestanding open reading frames (ORFs) of putative bacterial origin, including a large ORF (>8 kb) closely related to bacterial rhs-family genes. The cpDNA of T. expeditiones is 105,200 bp long and contains 125 unique genes. As in B. plumosa, several regions were identified with ORFs of possible bacterial origin, including genes involved in mobile functions (transposases, integrases, phage/plasmid DNA primases), and ORFs showing close similarity with bacterial DNA methyltransferases. The cpDNA of B. hypnoides differs from that of B. plumosa mainly in the presence of long intergenic spacers, and a large tRNA region. Chloroplast phylogenomic analyses were largely inconclusive with respect to monophyly of the Ulvophyceae, and the relationship of the Bryopsidales within the Chlorophyta.ConclusionsThe cpDNAs of B. plumosa and T. expeditiones are amongst the smallest and most gene dense chloroplast genomes in the core Chlorophyta. The presence of bacterial genes, including genes typically found in mobile elements, suggest that these have been acquired through horizontal gene transfer, which may have been facilitated by the occurrence of obligate intracellular bacteria in these siphonous algae.

Project description:BackgroundChlorophyceae is one of three most species-rich green algal classes and also the only class in core Chlorophyta whose monophyly remains uncontested as gene and taxon sampling improves. However, some key relationships within Chlorophyceae are less clear-cut and warrant further investigation. The present study combined genome-scale chloroplast data and rich sampling in an attempt to resolve the ordinal classification in Chlorophyceae. The traditional division into Sphaeropleales and Volvocales (SV), and a clade containing Oedogoniales, Chaetopeltidales, and Chaetophorales (OCC) was of particular interest with the addition of deeply branching members of these groups, as well as the placement of several incertae sedis taxa.MethodsWe sequenced 18 chloroplast genomes across Chlorophyceae to compile a data set of 58 protein-coding genes of a total of 68 chlorophycean taxa. We analyzed the concatenated nucleotide and amino acid datasets in the Bayesian and Maximum Likelihood frameworks, supplemented by analyses to examine potential discordant signal among genes. We also examined gene presence and absence data across Chlorophyceae.ResultsConcatenated analyses yielded at least two well-supported phylogenies: nucleotide data supported the traditional classification with the inclusion of the enigmatic Treubarinia into Sphaeropleales sensu lato. However, amino acid data yielded equally strong support for Sphaeropleaceae as sister to Volvocales, with the rest of the taxa traditionally classified in Sphaeropleales in a separate clade, and Treubarinia as sister to all of the above. Single-gene and other supplementary analyses indicated that the data have low phylogenetic signal at these critical nodes. Major clades were supported by genomic structural features such as gene losses and trans-spliced intron insertions in the plastome.DiscussionWhile the sequence and gene order data support the deep split between the SV and OCC lineages, multiple phylogenetic hypotheses are possible for Sphaeropleales s.l. Given this uncertainty as well as the higher-taxonomic disorder seen in other algal groups, dwelling on well-defined, strongly supported Linnaean orders is not currently practical in Chlorophyceae and a less formal clade system may be more useful in the foreseeable future. For example, we identify two strongly and unequivocally supported clades: Treubarinia and Scenedesminia, as well as other smaller groups that could serve a practical purpose as named clades. This system does not preclude future establishment of new orders, or emendment of the current ordinal classification if new data support such conclusions.

Dataset Information

Taxonomic scheme of the order Chaetophorales (Chlorophyceae, Chlorophyta) based on chloroplast genomes.

Publications

Taxonomic scheme of the order Chaetophorales (Chlorophyceae, Chlorophyta) based on chloroplast genomes.

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