Nucleic acid sequences from potato that encode the enzyme .beta.-solanine/.beta.-chaconine rhamnosyltransferase (SGT3) 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 SGT3 and thereby reduce levels of the predominant steroidal glycoalkaloids .alpha.-chaconine and .alpha.-solanine in Solanaceous plants such as potato are described.