Molecular evidence for a single common origin of chromalveolate plastids
Bibliographic record
Abstract
Plastids (photosynthetic organelles of plants and algae) are known to have spread between eukaryotic lineages by secondary endosymbiosis, or the uptake of a eukaryotic alga by another eukaryote, but the number of times this has taken place is controversial. This is particularly so in the case of eukaryotes with plastids derived from red algae, which are numerous and diverse. Despite their diversity, it has been suggested that all these eukaryotes share a recent common ancestor and that their plastids originated in a single endosymbiosis, the so‐called “chromalveolate hypothesis”. Here, we describe a novel molecular character that supports the chromalveolate hypothesis. Fructose‐1,6‐bisphosphate aldolase (FBA) is a glycolytic/Calvin cycle enzyme that exists as one of two non‐homologous types, class I and class II. Red algal plastid‐targeted FBA is a class I enzyme related to homologues from plants and green algae, and it would be predicted that the plastid‐targeted FBA from algae with red algal secondary endosymbionts should be related to this class I enzyme. However, we show that heterokonts, cryptomonads, haptophytes and dinoflagellates (all photosynthetic chromalveolates) encode two paralogous class II enzymes, one of which strongly supports a specific relationship between chromalveolates. Exactly where chromalveolates got their plastid‐targeted FBA genes is presently uncertain, but their common possession of this unexpected plastid characteristic is compelling evidence for their close relationship and a common origin for their plastids.
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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 | 0.000 |
| 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) | 0.001 | 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".