engleski

The plant genomes: between stability and evolutionary changes

Genomes of all living organisms are exposed to toxic agents from environment and products of cellular metabolism, which may cause DNA damage thus posing a serious threat to genome integrity and cell viability. We studied the mechanisms of DNA repair and recombination important for the genome stability in the plant model organism Arabidopsis thaliana. We comparatively analyzed three different Arabidopsis mutants for the MRE11 gene with respect to plant morphology, mitosis, meiosis, cell cycle control and DNA repair. As one of the mutants (mre11-2) was fully fertile although its Mre1 1 protein lacks the last 150 amino acids, we concluded that it’s C-terminus is dispensable for meiosis. Unexpectedly, introgression of this mutation into the atm mutant plant rendered the double mutant infertile, a phenotype not observed in either parent line. This data indicate that MRE11 partially compensates for ATM deficiency in meiosis of Arabidopsis. Furthermore, the same mutants were compared by a new arabidopsis genotoxic assay for in situ evaluation of the genome integrity and DNA damage repair efficiency after double strand break (DSB) induction. All mutants tested exhibited hypersensitivity to the bleomycin-treatment, and showed a G2/M checkpoint abrogation. These mutants also failed to transcriptionally induce several DDR genes and had altered expression of the CYCB1 ; 1::GUS protein. Nevertheless, numerous chromosomal fusions in the mre11 mutants, observed after the DNA damage induction, suggest intensive, but aberrant DNA repair activities, thus confirming that the full-length MRE11 is essential for the activation of the cell cycle arrest, transcriptional regulation and the DNA repair upon the induction of DSBs in Arabidopsis. Polyploidy is frequent in plants and some estimates suggest that 30–80% of living plant species are polyploid. Recently we successfully reconstructed the parental origin of triploid onion Allium × cornutum, widespread in south Asia and Europe, and known in Croatia under the name ‘Ljutika’. The phylogenetic analysis of two types of ribosomal genes and their chromosome mapping in triploid hybrid and its wild relatives enabled the confirmation of its complex triparental origin and revealed the identity of all three putative parental species.

DNA repair; MRE11; genome stability; cell cycle; meiosis; polyploidy

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