Silencing onion lachrymatory factor synthase causes a significant change in the sulfur secondary metabolite profile

Plant Physiol. 2008 Aug;147(4):2096-106. doi: 10.1104/pp.108.123273. Epub 2008 Jun 26.


Through a single genetic transformation in onion (Allium cepa), a crop recalcitrant to genetic transformation, we suppressed the lachrymatory factor synthase gene using RNA interference silencing in six plants. This reduced lachrymatory synthase activity by up to 1,544-fold, so that when wounded the onions produced significantly reduced levels of tear-inducing lachrymatory factor. We then confirmed, through a novel colorimetric assay, that this silencing had shifted the trans-S-1-propenyl-l-cysteine sulfoxide breakdown pathway so that more 1-propenyl sulfenic acid was converted into di-1-propenyl thiosulfinate. A consequence of this raised thiosulfinate level was a marked increase in the downstream production of a nonenzymatically produced zwiebelane isomer and other volatile sulfur compounds, di-1-propenyl disulfide and 2-mercapto-3,4-dimethyl-2,3-dihydrothiophene, which had previously been reported in trace amounts or had not been detected in onion. The consequences of this dramatic simultaneous down- and up-regulation of secondary sulfur products on the health and flavor attributes of the onion are discussed.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Carbon-Sulfur Lyases / metabolism
  • Molecular Sequence Data
  • Onions / enzymology
  • Onions / genetics*
  • Onions / metabolism
  • Phenotype
  • Plant Proteins / genetics*
  • Plant Proteins / metabolism
  • Protein Precursors / genetics
  • Protein Precursors / metabolism
  • RNA Interference*
  • RNA, Messenger / metabolism
  • Sulfinic Acids / analysis
  • Sulfinic Acids / chemistry
  • Sulfur / chemistry
  • Sulfur / metabolism*
  • Transformation, Genetic
  • Volatilization


  • Plant Proteins
  • Protein Precursors
  • RNA, Messenger
  • Sulfinic Acids
  • bis(1-propenyl)thiosulfinate
  • Sulfur
  • Carbon-Sulfur Lyases
  • alliin lyase

Associated data

  • GENBANK/AB089203