The Complete Mitochondrial DNA Sequence of the Green Alga Pseudendoclonium akinetum (Ulvophyceae) Highlights Distinctive Evolutionary Trends in the Chlorophyta and Suggests a Sister-Group Relationship Between the Ulvophyceae and Chlorophyceae
Bibliographic record
Abstract
The mitochondrial genome has undergone radical changes in both the Chlorophyta and Streptophyta, yet little is known about the dynamics of mtDNA evolution in either of these lineages. In the Chlorophyta, which comprises four of the five recognized classes of green algae (Prasinophyceae, Trebouxiophyceae, Ulvophyceae, and Chlorophyceae), the mitochondrial genome varies from 16 to 55 kb. This genome has retained a compact gene organization and a relatively complex gene repertoire ("ancestral" pattern) in the basal lineages represented by the Trebouxiophyceae and Prasinophyceae, whereas it has been reduced in size and gene complement and tends to evolve much more rapidly at the sequence level ("reduced-derived" pattern of evolution) in the Chlorophyceae and the lineage leading to the enigmatic chlorophyte Pedinomonas. To gain information about the evolutionary trends of mtDNA in the Ulvophyceae and also to gain insights into the phylogenetic relationships between ulvophytes and other chlorophytes, we have determined the mtDNA sequence of Pseudendoclonium akinetum. At 95,880 bp, Pseudendoclonium mtDNA is the largest green-algal mitochondrial genome sequenced to date and has the lowest gene density. These derived features are reminiscent of the "expanded" pattern exhibited by embryophyte mtDNAs, indicating that convergent evolution towards genome expansion has occurred independently in the Chlorophyta and Streptophyta. With 57 conserved genes, the gene repertoire of Pseudendoclonium mtDNA is slightly smaller than those of the prasinophyte Nephroselmis olivacea and the trebouxiophyte Prototheca wickerhamii. This ulvophyte mtDNA contains seven group I introns, four of which have homologs in green-algal mtDNAs displaying an "ancestral" or a "reduced-derived" pattern of evolution. Like its counterpart in the chlorophycean green alga Scenedesmus obliquus, it features numerous small, dispersed repeats in intergenic regions and introns. Its overall rate of sequence evolution appears to be accelerated to an intermediary level as compared with the rates observed in "ancestral" and "reduced-derived" mtDNAs. In agreement with the finding that Pseudendoclonium mtDNA exhibits features typical of both the "ancestral" and "reduced-derived" patterns of evolution, phylogenetic analyses of seven mtDNA-encoded proteins revealed a sister-group relationship between this ulvophyte and chlorophytes displaying "reduced-derived" mtDNAs.
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How this classification was reachedexpand
Full frame distilled prediction
Teacher imitationNot calibrated prevalence, not ground truth. Human validation pending. Learned from the 10,348 direct Codex labels and 10,348 direct Gemma labels. Candidate is the union of thresholded teacher heads; consensus is their intersection. These outputs are machine_predicted_unvalidated and are not human labels or direct frontier model labels.
Codex and Gemma teacher scores by category
| Category | Codex | Gemma |
|---|---|---|
| Metaresearch | 0.000 | 0.000 |
| Meta-epidemiology (narrow) | 0.000 | 0.000 |
| Meta-epidemiology (broad) | 0.000 | 0.000 |
| Bibliometrics | 0.000 | 0.000 |
| Science and technology studies | 0.001 | 0.001 |
| Scholarly communication | 0.000 | 0.000 |
| Open science | 0.000 | 0.000 |
| Research integrity | 0.000 | 0.000 |
| Insufficient payload (model declined to judge) | 0.000 | 0.000 |
Machine scores (provisional)
The two teacher heads of the student model, read on this work. A score orders the frame for review; it never asserts a category, and the validation status ships verbatim with every row.
Baseline scores from an immature model (maturity gate not passed, 7 training rounds). Scores rank; they never assert a category.
score_only:v0-immature-baseline · verbatim from the scoring run: score_only means the number may rank works, and no category label ships from itClassification
machine, unvalidatedMachine predicted; a candidate call from one teacher head, not a consensus.
How this classification was reached, model by model and score by score, is at the end of the page under "How this classification was reached".