MANIPULATION AND COMPENSATION OF STEROIDAL GLYCOALKALOID BIOSYNTHESIS IN POTATOES

Steroidal glycoalkaloids (SGAs) are undesirable secondary metabolites produced in solanaceous plants including potato, tomato and eggplant. Two tri-glycosylated alkaloids, α-chaconine and α-solanine, occur naturally in potato tubers and can accumulate to excessive levels due to mechanical, environmental, and genetic perturbations. We have identified members of the steroidal-alkaloid glycosyl transferasese (Sgt) gene family coding the UDP-galactose: solanidine galactosyltransferase (Sgt1), the UDP-glucose:solanidine glucosyltransferase (Sgt2), and the UDP-rhamnose:β-solanine/β-chaconine rhamnosyltransferase (Sgt3). Reverse genetic manipulation of the Sgt gene family members using transgenic lines expressing active antisense gene constructs results in a shift of SGA pathway flux, in turn resulting in compensation by other pathway intermediates and products. New Sgt gene family members are being studied to verify the substrate specificity and biosynthetic sequence. Additional studies are underway to use the members of this gene family to completely block accumulation of SGAs in tubers.