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The question

Could we genetically engineer a no-cry onion that tastes exactly like a regular onion? Work out the mechanism behind onion tears, what happens to the flavor chemistry when that pathway is blocked, what has actually been tried, and propose the one experiment that would settle whether flavor survives.

Asked in Omic Discover on 8 September 2026. No edits to the question, no retries. The recording above walks through the finished run: the question, the plan, the 25 references, the hypothesis tournament, the answer and the knowledge gap. The live run took about eleven minutes.

What Omic did

  1. Planned four stages: literature search, source retrieval, hypothesis generation, synthesis.
  2. Searched six sources (Google Scholar, PubMed Central, OpenAlex, CrossRef, others, and its own paper index): 842 raw results, deduplicated and ranked to 25.
  3. Read the primary sources it could reach: full sections from nine papers, abstracts from five.
  4. Generated and scored three mechanistic hypotheses for what happens to flavor when lachrymatory factor synthase (LFS) is silenced, each judged on novelty, testability, plausibility and falsifiability.
  5. Synthesized one answer with numbered citations, an explicit knowledge gap, and the experiment that would close it.

What it found

  • The tear mechanism is settled science: alliinase produces 1-propenesulfenic acid, and LFS converts it to the lachrymatory factor. Silencing LFS (RNAi, and more recently CRISPR/Cas9) removes the tears.
  • Blocking LFS reroutes the sulfur chemistry toward thiosulfinates, shifting the volatile profile toward sweeter, more garlic-like notes.
  • The knowledge gap: no published sensory study compares LFS-silenced onions with conventional ones. Claims that they taste the same are inferences from chemistry, not from panels.
  • The experiment: grow LFS-silenced and wild-type onions under identical conditions, quantify the lachrymatory factor and rerouted volatiles after standardized wounding, and run triangle tests with a trained panel on raw and cooked preparations.

The answer, as Omic wrote it

Reproduced from the run without edits, other than formatting. Bracketed numbers are Omic’s own citation markers; the sources are listed below.

Key finding. Engineering ‘no-cry’ onions by silencing Lachrymatory Factor Synthase (LFS) effectively eliminates tear production but significantly alters sulfur volatile chemistry, making sensory equivalence to conventional onions unlikely without empirical testing.

The tear pathway is among the best-established pieces of onion biochemistry. The precursor trans-S-1-propenyl-L-cysteine sulfoxide (isoalliin, 1-PRENCSO) sits in the cytoplasm, while alliinase is sequestered in the vacuole; tissue damage brings them together. Alliinase (a C–S lyase) cleaves isoalliin into highly reactive 1-propenesulfenic acid plus aminoacrylic acid. A dedicated enzyme, lachrymatory factor synthase (LFS), converts 1-propenesulfenic acid into (Z)-propanethial S-oxide; alliinase alone generates “a plethora of downstream organosulfur compounds” but no lachrymatory factor. Silvaroli et al. solved the LFS crystal structure, showing a helix-grip fold of the plant START-domain superfamily, most similar to abscisic-acid receptors of the PYL family. The internal cavity is shrunken to ~216 ų and made more hydrophobic, tailored to the small 1-propenesulfenic acid substrate [1, 7].

Two independent RNAi efforts established that LFS suppression does not just delete a compound; it reroutes the whole downstream sulfur cascade. Eady et al. silenced LFS in six transformed onion plants, cutting LFS activity by up to 1,544-fold, with significantly reduced lachrymatory factor production on wounding. A colorimetric assay showed the breakdown of isoalliin was shifted so that more 1-propenyl sulfenic acid became di-1-propenyl thiosulfinate, with marked increases in a zwiebelane isomer, di-1-propenyl disulfide, and 2-mercapto-3,4-dimethyl-2,3-dihydrothiophene, compounds previously found only in trace amounts or never in onion. Kamata et al., using an autofluorescence-based selection of transformable calli, recovered four independent transgenic lines with LFS transcript at 3.2–11.0% of wild-type, LFS protein at 0.09–20.7%, and enzyme activity at 0.3–10.1%; their thiosulfinate assay indicated a significant increase in thiosulfinate formation specifically when LFS activity fell to roughly 1% or below wild-type. In a normal onion, di-1-propenyl thiosulfinate has never been reported; instead LF, 1-propenyl methane thiosulfinate, and dipropyl disulfide dominate, and it has long been hypothesized that LF production actively suppresses the other predicted volatiles. In other words, LFS is the branch point that makes onion “onion” rather than “garlic-like”: garlic’s major sulfoxide (alliin) yields thiosulfinates, whereas onion’s major sulfoxide (isoalliin) is diverted into LF. A modern analytical method confirms LF is a minority species even in normal onion headspace, about 4.5% of total sulfur-compound area versus 19.4% for 2,4-dimethyl-thiophene, underscoring that the tear gas is one flavor-relevant volatile among many. The likely sensory consequence is a shift from lachrymatory pungency toward the sweet, garlic-like notes of thiosulfinate chemistry. But flavor is multimodal (taste, aroma and trigeminal irritation), so removing the irritant component changes the percept even if every volatile matched [2, 3, 14].

Knowledge gap. Crucially, no published sensory studies directly compare the flavor profiles of LFS-suppressed onions with their conventional counterparts. Claims of “tasting exactly like a regular onion” are inferences based on volatile chemistry rather than empirical sensory data. The impact of removing the lachrymatory factor, which contributes to pungency and overall flavor, on perceived taste and aroma remains largely unquantified by trained sensory panels.

Current commercial tearless-type cultivars such as Vidalia achieve mildness through deficient sulfur uptake or sulfur-poor soils, but in doing so they accumulate fewer secondary sulfur compounds, “reducing their sensory and health qualities compared with more pungent high-sulfur cultivars.” The New Zealand and Japanese team produced LFS-silenced onions via Agrobacterium-mediated transformation, recovering four independent transgenic lines with quantitative knockdowns. A 2026 bioRxiv preprint reports the first CRISPR/Cas9 editing of the onion LFS gene; mutations were confirmed, and regenerated plants had lower LFS enzyme activity. However, the edited plants exhibited severe growth abnormalities and failed to set seed, possibly due to the long-term culture needed to maintain the elite callus line. LFS suppression is expected to raise thiosulfinates and their derivatives, compounds “associated with the characteristic flavor and various health effects,” and onion sulfur compounds such as onionin A have reported antitumor activity in mouse models [3, 5, 9].

The definitive experiment to assess flavor equivalence has not yet been performed. It would require growing LFS-silenced and wild-type onions under identical conditions, then performing time-resolved quantification of both the lachrymatory factor and the rerouted sulfur volatiles (thiosulfinates, disulfides, dihydrothiophenes) after standardized wounding. Crucially, this chemical data must be paired with sensory analysis from a trained panel using triangle tests on both raw and cooked preparations. If panelists cannot distinguish the edited onions from wild-type in overall flavor, despite documented chemical differences, then flavor survival would be empirically demonstrated.

Emerging trend. CRISPR/Cas9 genome editing for LFS suppression is a newer, more precise approach than RNAi. Early results show the gene can be edited, but the reported growth abnormalities and failure to set seed highlight the gap between a precise edit and an agronomically viable crop.

Where Omic suggested going next. The quantitative volatile difference between LFS-silenced and wild-type onions, raw and cooked. Whether trained panels can tell them apart, and on what. And what causes the growth and seed-set failures in the CRISPR-edited lines.

Sources cited in the answer

  1. Silvaroli, J. A. et al. (2017). Enzyme That Makes You Cry: Crystal Structure of Lachrymatory Factor Synthase from Allium cepa. ACS Chemical Biology.
  2. Kamata, Y. et al. (2011). A novel autofluorescence-based selection of calli amenable to Agrobacterium-mediated transformation in onion (Allium cepa L.). Plant Biotechnology.
  3. Eady, C. C. et al. (2008). Silencing onion lachrymatory factor synthase causes a significant change in the sulfur secondary metabolite profile. Plant Physiology.
  4. Tamaru, S. et al. (2026). Generation of lachrymatory factor synthase-suppressed onion (Allium cepa L.) by Agrobacterium-mediated gene transfer for CRISPR/Cas9 genome editing. bioRxiv preprint.
  5. He, Q. et al. (2011). First insights into the mode of action of a “lachrymatory factor synthase”: implications for the mechanism of lachrymator formation in Petiveria alliacea, Allium cepa and Nectaroscordum species. Phytochemistry.
  6. Nohara, T. & Fujiwara, Y. (2017). Antitumor Sulfur Compounds from Allium Species (Onion, Welsh Onion, and Garlic). Natural Product Communications.
  7. Application of Direct Thermal Desorption–Gas Chromatography–Mass Spectrometry for Determination of Volatile and Semi-Volatile Organosulfur Compounds in Onions (2023).

Omic ranked 25 references in total; the seven above are the ones the answer cites.

What this does and does not show

It shows a real, unedited Omic investigation on a question with no internal data attached. It does not show an organizational fabric at work: there were no company notebooks or prior results for this question, so the answer comes from the literature alone. It is a literature-based investigation and proposal, not an experimental result.