title: Silencing onion lachrymatory factor synthase causes a significant change in the sulfur secondary metabolite profile.
abstract: 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.
authors.affiliation: National Centre for Advanced Bio-Protection Technologies, Lincoln University, Christchurch 7647, New Zealand. eadyc@crop.cri.nz
authors.forename: Colin C
authors.initials: CC
authors.lastname: Eady
authors.forename: Takahiro
authors.initials: T
authors.lastname: Kamoi
authors.forename: Masahiro
authors.initials: M
authors.lastname: Kato
authors.forename: Noel G
authors.initials: NG
authors.lastname: Porter
authors.forename: Sheree
authors.initials: S
authors.lastname: Davis
authors.forename: Martin
authors.initials: M
authors.lastname: Shaw
authors.forename: Akiko
authors.initials: A
authors.lastname: Kamoi
authors.forename: Shinsuke
authors.initials: S
authors.lastname: Imai
mesh_terms: D013437:Carbon-Sulfur Lyases / Q000378:metabolism; D008969:Molecular Sequence Data; D019697:Onions / Q000201:enzymology / Q000235:genetics* / Q000378:metabolism; D010641:Phenotype; D010940:Plant Proteins / Q000235:genetics* / Q000378:metabolism; D011498:Protein Precursors / Q000235:genetics / Q000378:metabolism; D034622:RNA Interference; D012333:RNA, Messenger / Q000378:metabolism; D013441:Sulfinic Acids / Q000032:analysis / Q000737:chemistry; D013455:Sulfur / Q000737:chemistry / Q000378:metabolism*; D014170:Transformation, Genetic; D014835:Volatilization
chemical_list: D010940:Plant Proteins; D011498:Protein Precursors; D012333:RNA, Messenger; D013441:Sulfinic Acids; C467562:bis(1-propenyl)thiosulfinate; D013455:Sulfur; D013437:Carbon-Sulfur Lyases; C019243:alliin lyase