Glucosyltransferases were isolated and characterised from many plant sources. The enzymes show middle amino acid similarity and broad substrate specificity. The promoter of the potato 5-UGT gene reveals strong environmental induction. The activation of the gene expression by UV radiation, ABA and cold treatments was detected. Overexpression of 5-UGT resulted in the accumulation of the diglucoside derivative of petunidin in transgenic tubers; the latter is most probably the reason for plant resistance to pathogen infection. Overexpressing plants produced more tubers, and the overall yield was higher when compared to nontransformants.