Genome-wide variation of the somatic mutation frequency in transgenic plants

In order to analyse the frequency of point mutations in whole plants, sever al constructs containing single nonsense mutations in the beta-glucuronidas e (uidA) gene were used to generate transgenic Arabidopsis thaliana plants. Upon histochemical staining of transgenic plants, sectors indicative of tr ansgene reactivation appeared. Reversion frequencies were in the range of 1 0(-7)-10(-8) events per base pair, exceeding the previous estimates for oth er eukaryotes at least 100-fold. The frequency was dependent on the positio n of the mutation substrate within the transgene and the position of the tr ansgene within the Arabidopsis genome. An inverse relationship between the level of transgene transcription and mutation frequency was observed in sin gle-copy lines. DNA-damaging factors induced the mutation frequency by a fa ctor of up to 56 for UV-C, a factor of 3 for X-rays and a factor of 2 for m ethyl methanesulfonate. This novel plant mutation-monitoring system allowed us to measure the frequencies of point mutation in whole plants and may be used as an alternative or complement to study the mutagenicity of differen t environmental factors on the higher eukaryote's genome.