|Belknap, William - Bill|
Submitted to: Potato Association of America Proceedings
Publication Type: Abstract only
Publication Acceptance Date: 8/10/2003
Publication Date: 8/10/2003
Citation: MC CUE, K.F., SHEPARD, L.V., ALLEN, P.V., MACCREE, M.M., ROCKHOLD, D.R., DAVIES, H.V., BELKNAP, W.R. 2003. MODIFIED STEROIDALALKALOID BIOSYNTHESIS IN TRANSGENIC TUBERS CONTAINING AN ANTISENSE STEROL GLYCO TRANSFERASE (SGT) GENE ENCODING A NOVEL ALKALOID DIGLYCOSIDE RHAMNOSYL TRANSFERASE. POTATO ASSOCIATION OF AMERICA PROCEEDINGS. 80(4):32. Interpretive Summary:
Technical Abstract: Steroidal Glyco Alkaloids (SGAs) are undesirable naturally occurring secondary metabolites in potatoes. SGA levels are dependent upon both variety and growth/storage conditions. In an effort to control the accumulation of SGAs we have introduced antisense transgene constructs encoding enzymes of the biosynthetic pathway. Transcription of the antisense transgenes in directed from the Granule Bound Starch Synthase promoter, to alter accumulation in the tuber without affecting levels in the aerial portions of the plant. We report here the isolation and effects of a gene encoding an enzyme for the final step in the production of the two major SGAs of potato, a-solanine and a-chaconine, the addition of the 2-a-D rhamnosyl moiety of the triose sidechain. We have designated this gene SOLtu:Sgt3 and the enzyme is a novel E.C. 2.4.1.X Sterol Glycosyl Transferase (SGT) catalyzing b-solanine/ b-chaconine :UDP-rhamnose 1®2 rhamnosyltransferase, [UDP-rhamnose: 2-a-(3-b galactosyl 3-b glucosylpyranoside ) sterol rhamnosyltransferase and UDP-rhamnose: 2-a-(3-b glucosyl 4-a-rhamnosylpyranoside ) sterol rhamnosyltransferase]. Examination by HPLC and MS of alkaloids extracted from dried tuber slices identified transgenic lines with modified SGA profiles. The most dramatic effect in selected transgenic lines was a severe reduction in the accumulation of a-solanine and a-chaconine with a subsequent accumulation of b-solanine and b-chaconine the immediate precursors. These data provide evidence that a single or highly conserved enzyme is responsible for addition of the final rhamnosyl unit to the triose side chain of both of the major potato SGAs.