Salicylic acid biosynthesis via the PAL pathway requires benzaldehyde synthase and a benzyl salicylate-specific esterase
Bibliographic record
Abstract
Salicylic acid (SA) biosynthesis in plants occurs via the isochorismate synthase (ICS) and phenylalanine ammonia-lyase (PAL) pathways. The critical steps from benzyl-CoA to SA in the PAL-mediated pathway remain unknown. To probe benzenoid metabolism, we generated CRISPR/Cas9-mediated knockouts of benzaldehyde synthase in poplar. These plants produce less benzyl benzoate, benzyl salicylate and SA, yet accumulate more benzoic acid. We show that HSR203J encodes a carboxylesterase that specifically hydrolyzes benzyl salicylate. Virus-induced gene silencing (VIGS) of HSR203J in Nicotiana benthamiana led to reduced benzyl salicylate hydrolysis to SA. Based on these data, we propose a biosynthesis model and provide evidence that benzoyl-CoA is esterified to benzyl benzoate and converted to benzyl salicylate, which then releases SA. In addition, we identified a pathogen-induced cytochrome P450 encoded by HSR515 as a putative benzyl benzoate 2-hydroxylase. VIGS-mediated suppression of HSR515 in N. benthamiana reduced the conversion of benzyl benzoate to SA. Phylogenetic analyses indicated that Brassicaceae genomes do not contain HSR203J and HSR515 orthologs, whereas these genes are present in other vascular plants. These findings represent an important advance in our understanding of SA biosynthesis and identify missing steps in the PAL-mediated SA biosynthetic pathway.
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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".