Nucleic acid sequences from potato that encode the enzyme UDP-glucose:solanidine glucosyltransferase (SGT2) are disclosed. Recombinant DNA molecules containing the sequences, and use thereof, in particular, use of the sequences and antisense constructs to inhibit the production of SGT2 and thereby reduce the level of the more human-toxic of the two predominant steroidal glycoalkaloids .alpha.-chaconine and/or increase the level of the more insect-toxic .alpha.-solanine in Solanaceous plants such as potato are described.