The Chloroplast Genome Sequence of the Green Alga Pseudendoclonium akinetum (Ulvophyceae) Reveals Unusual Structural Features and New Insights into the Branching Order of Chlorophyte Lineages
Bibliographic record
Abstract
One major lineage of green plants, the Chlorophyta, is represented by the green algal classes Prasinophyceae, Ulvophyceae, Trebouxiophyceae, and Chlorophyceae. The Prasinophyceae occupies the most basal position in the Chlorophyta, but the branching order of the Ulvophyceae, Trebouxiophyceae, and Chlorophyceae remains unresolved. The chloroplast genome sequences currently available for representatives of three chlorophyte classes have revealed that this genome is highly plastic, with Chlamydomonas (Chlorophyceae) and Chlorella (Trebouxiophyceae) showing fewer ancestral features than Nephroselmis (Prasinophyceae). We report the 195,867-bp chloroplast DNA (cpDNA) sequence of Pseudendoclonium akinetum (Ulvophyceae), a member of the class that has not been previously examined for detailed cpDNA analysis. This genome shares common evolutionary trends with its Chlorella and Chlamydomonas homologs. The gene content, number of ancestral gene clusters, and abundance of short dispersed repeats in Pseudendoclonium cpDNA are intermediate between those observed for Chlorella and Chlamydomonas cpDNAs. Although Pseudendoclonium cpDNA features a large inverted repeat, its quadripartite structure is unusual in displaying an rRNA operon transcribed toward the large single-copy (LSC) region and a small single-copy region containing 14 genes that are normally found in the LSC region. Twenty-seven group I introns lie in nine genes and fall within four subgroups (IA1, IA2, IA3, and IB); 19 encode putative homing endonucleases, and 7 have homologs at identical insertion sites in other chlorophyte or streptophyte organelle genomes. The high similarity observed among the 14 IA1 and 7 IA2 introns and their encoded endonucleases suggests that many introns arose from intragenomic proliferation of a few founding introns in the lineage leading to Pseudendoclonium. Interestingly, one intron (in atpA) and some of the dispersed repeats also reside in Pseudendoclonium mitochondria, providing strong evidence for interorganellar lateral transfer of these genetic elements. Phylogenetic analyses of 58 cpDNA-encoded proteins and genes support the hypothesis that the Ulvophyceae is sister to the Trebouxiophyceae but cannot eliminate the hypothesis that the Ulvophyceae is sister to the Chlorophyceae. We favor the latter hypothesis because it is strongly supported by phylogenetic analyses of gene order data and by independent structural evidence based on shared gene losses and rearrangement break points within ancestrally conserved gene clusters.
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How this classification was reachedexpand
Full frame machine prediction
Teacher imitationNot calibrated prevalence, not ground truth. Human validation pending. The Gemma side is a direct model label for every work in the frame, read from the title-only record. The Codex side is a classifier learned from the 10,348 direct Codex labels and calibrated to design-weighted sample rates; fields without enough sample support carry no Codex call. Candidate is the union of the two sides; consensus is their intersection. These outputs are machine_predicted_unvalidated and are not human labels.
Distilled classifier scores by category (both heads)
| 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 | 0.001 |
| Science and technology studies | 0.000 | 0.000 |
| 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 source (direct Gemma or distilled Codex), 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".