Submitted to: American Journal of Potato Research
Publication Type: Abstract Only
Publication Acceptance Date: 3/11/2005
Publication Date: 4/10/2005
Citation: Mc Cue, K.F., Allen, P.V., Shepherd, L., Blake, A., Whitworth, J.L., Rockhold, D.R., Stewart, D., Davies, H., Belknap, W.R. 2005. Identification and characterization of a novel udp-glucose: solanidine glucosyl transferase at the committed step in steroidal glycoalkaloid biosynthesis in potatoes. American Journal of Potato Research. 83 (1): 123 Interpretive Summary: We are exploring methods using naturally occurring genes from potato to reduce the accumulation of the steroidal glycoalkaloids (SGAs), undesirable natural metabolites that accumulate in and under the skin of potatoes. Transgenic potato plants expressing a copy of the sterolalkaloid glycosyl transferase gene (Sgt2) in the backwards orientation shows inhibition of the most abundant and least desirable end product alpha-chaconine. Studies using purified protein produced in yeast cells has confirmed the biochemical function of the SGT2 protein in SGA production as the UDP-glucose:solanidine glucosyl transferase.
Technical Abstract: Steroidal glycoalkaloids (SGAs) are undesirable secondary metabolites in the Solanaceous plants potato and tomato. Two tri-glycosylated alkaloids, alpha-chaconine and alpha-solanine accumulate in potato tubers. A new sterol alkaloid glycosyltransferase (Sgt) gene has been identifed. The Sgt2 nucleic acid sequence is 68% identical to Sgt1 a UDP-galactose:solanidine galactosyl transferase. The predicted SGT2 sequence shows 63% amino acid identity and 80% similarity with the SGT1 protein. Sgt2 and Sgt1 have similar wound-induced expression of RNA in tubers with transcripts accumulating to a maximum within the first 16 hours after wounding and then rapidly declining. Analysis of genomic DNA shows a simple pattern for Sgt2 indicative of low copy number. An amino terminal fragment of Sgt2 was used to create an antisense transgene under control the Gbss6 promoter and the Ubi3 polyadenylation signal. Analysis of total SGAs in glass house tubers of cv. Desiree and field grown tubers of cv. Lenape showed differences attrributable to somaclonal variation. However, the profiles of component SGAs were altered in some of the antisense lines showing large reductions in alpha-chaconine usually compensated by an increase alpha-solanine. Analysis of recombinant SGT2 protein purified from yeast cultures deomonsrated the specifiicity of SGT2 for UDP-glucose confiriming its function as a UDP-glucose:solanidine glucosyl transferase.