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SYSTEMS BIOLOGY, MOLECULAR BIOLOGY, AND GENE REGULATION

Silencing Onion Lachrymatory Factor Synthase Causes a Significant Change in the Sulfur Secondary Metabolite Profile^1,[W],[OA]

National Centre for Advanced Bio-Protection Technologies, Lincoln University, Christchurch 7647, New Zealand (C.C.E., T.K.); New Zealand Institute for Crop and Food Research Limited, Christchurch 8140, New Zealand (C.C.E., N.G.P., S.D., M.S.); and House Foods Corporation, Yotsukaido, Chiba 284–0033, Japan (T.K., M.K., A.K., S.I.)

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.

The author responsible for distribution of materials integral to the findings presented in this article in accordance with the policy described in the Instructions for Authors (www.plantphysiol.org) is: Colin C. Eady (eadyc{at}crop.cri.nz).

^[W] The online version of this article contains Web-only data.

^[OA] Open Access articles can be viewed online without a subscription.

www.plantphysiol.org/cgi/doi/10.1104/pp.108.123273

^* Corresponding author; e-mail eadyc{at}crop.cri.nz.

Received May 22, 2008; accepted June 10, 2008; published June 26, 2008.

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Plant Physiol. 2008 147: 1761-1762. [Full Text]