Dissimilar mutation and recombination rates in Arabidopsis and tobacco

Previous studies have shown that genome evolution was accompanied by the number of various genome rearrangements. Large deletions, insertions and gene duplications are the major cause of genome reshuffling, however, high sequence polymorphism between closely related species suggests that point mutations are the most frequent outcome of repair malfunction. Recent data suggests that Arabidopsis and tobacco plants repair double strand breaks (DSB) with different precision. To analyze the possible contribution of DNA repair mechanisms to the maintenance of the genome size, we compared the mutation and recombination rate between Arabidopsis and tobacco plants-both dicot species with differing genome size. The mutation rate was analyzed in several tobacco and Arabidopsis lines transgenic for a stop-codon-inactivated beta-glucuronidase gene. We found 5.4-fold higher spontaneous and 2.9-fold higher ultraviolet C (UVC)-induced mutation rates in tobacco. The homologous recombination (HR) was analyzed in Arabidopsis and tobacco lines which carried luciferase-based recombination substrate. The estimated recombination rate was as many as 75-fold higher in tobacco. Our data suggest that tobacco employ the homologous recombination pathway for the repair of breaks more frequently than Arabidopsis. Combining this data with previous findings it is possible to suggest that the difference in the ratio between homologous recombination and non-homologous end-joining (NHEJ) influences genome size of the analyzed plants. (C) 2003 Elsevier Ireland Ltd. All rights reserved.