engleski

LTR-retrotransposons as molecular tools for the study of homologous recombination in plants

After the establishment of the complete sequence of the genome of plant Arabidopsis thaliana a major effort was started to elucidate the biological function of all open reading frames of this organism. Methods for targeted gene replacement via homologous recombination (HR) would be ideal for this purpose. However, over the past years all attempts to establish an efficient gene targeting technique in flowering plants were in the end not successful mainly due to low frequency of HR in plant somatic cells. The study of HR is often based on artificial closely spaced direct repeats inserted intio the genome. In various experiments using different plants and conditions the frequency of HR between such repeats was in range form 10-4 to 10-7. Long Terminal Repeat (LTR) containing retrotransposons resebmle in overall structure substrates used for the study of HR. They contain one or two open reading frames flanked by direct repeats (LTRs). In our study of the activity of LTR-retrotransposon Tto1 in the plant A. thaliana Col-O all potentially active elements were destroyed via homologous recombination between LTRs of each element. In contrast, mutated retroelements can be stable maintained in the Arabidopsis Col-O genome. Nevertheless, the same experimental approach with the ecotype Wassilewskija did not lead to extremely high frequency of HR. The results suggest the existence of genotype-specific mechanism in A. thaliana Col-O involved in homologous recombination, which is activated by retrotransposons. The evaluation of factors responsible for elimination of active retrotransposons via HR might help to set up a general applicable technique for efficient gene targeting in plants.

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