A DNA molecule is provided which comprises a sequence according to SEQ ID NO: 8 having an open reading frame from base pair 227 to base pair 1831 or having at least 50% homology to the above-indicated sequence, or hybridizing with the above-indicated sequence under stringent conditions, or comprising a sequence which has degenerated to the above-indicated DNA sequence because of the genetic code, the sequence coding for a plant protein having .beta.1,2-xylosyltransferase activity or being complementary thereto.