Two Oxidosqualene Cyclases Responsible for Biosynthesis of Tomato Fruit Cuticular Triterpenoids
Bibliographic record
Abstract
The first committed step in triterpenoid biosynthesis is the cyclization of epoxysqualene into various triterpene alcohol isomers, a reaction catalyzed by oxidosqualene cyclases (OSCs). The different OSCs have characteristic product specificities, which are mainly due to differences in the numbers of high-energy intermediates the enzymes can stabilize. The goal of this investigation was to clone and characterize OSCs from tomato (Solanum lycopersicum), a species known to accumulate δ-amyrin in its fruit cuticular wax, in order to gain insights into the enzymatic formation of this particular triterpenoid. We used a homology-based approach to isolate two tomato OSCs and tested their biochemical properties by heterologous expression in yeast as well as overexpression in tomato. One of the enzymes was found to be a product-specific β-amyrin synthase, while the other one was a multifunctional OSC synthesizing 48% δ-amyrin and six other products. The product spectra of both OSCs together account for both the range and the relative amounts of the triterpenoids found in the fruit cuticle. Both enzymes were expressed exclusively in the epidermis of the tomato fruit, indicating that their major function is to form the cuticular triterpenoids. The relative expression levels of both OSC genes, determined by quantitative reverse transcription-polymerase chain reaction, were consistent with product profiles in fruit and leaves of the tomato cultivar MicroTom. However, the transcript ratios were only partially consistent with the differences in amounts of product triterpenoids between the tomato cultivars MicroTom, M82, and Ailsa Craig; thus, transcriptional control of the two OSCs alone cannot explain the fruit triterpenoid profiles of the cultivars.
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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 | 0.001 |
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".