SOMATIC INTRACHROMOSOMAL HOMOLOGOUS RECOMBINATION EVENTS IN POPULATIONS OF PLANT SIBLINGS

Intrachromosomal homologous recombination in whole tobacco plants was analyzed using beta-glucuronidase as non-selectable marker. We found t hat recombination frequencies were additive for transgenes in allelic positions and could be enhanced by treatment of plants with DNA-damagi ng agents. We compared the patterns of distribution of recombination e vents of different transgenic lines of tobacco and Arabidopsis with th e respective Poisson distributions. Some lines showed Poisson-like dis tributions, indicating that recombination at the transgene locus was o ccurring in a random fashion in the plant population. In other cases, however, the distributions deviated significantly from Poisson distrib utions indicating that for specific transgene loci and/or configuratio ns recombination events are not randomly distributed in the population . This was due to overrepresentation of plants with especially many as well as especially few recombination events. Analysis of one tobacco line indicated furthermore that the distribution of recombination even ts could be influenced by treating the seedlings with external factors . Our results suggest that different plant individuals, or parts of th em, might exhibit different transient 'states' of recombination compet ence. A possible model relating 'recombination silencing' and transcri ption silencing to heterochromatization of the transgene locus is disc ussed.