engleski

Mre11 IS REQUIRED FOR REPAIR BUT NOT FOR THE INDUCTION OF Spo11 DEPENDANT MEIOTIC DNA BREAKS IN ARABIDOPSIS

The Mre11/Rad50/Nsb1 complex is involved in several fundamental aspects of chromosome maintenance ; the DNA checkpoint, double-strand break (DSB) repair, telomere maintenance and meiosis. Its inactivation is lethal for vertebrate cells, but not for plants thus providing an opportunity to study the consequences of its defects in higher eucaryotes. To examine the role of Mre11 in meiosis we obtained two T-DNA insertion lines of Arabidopsis. Plants homozygous for a T-DNA insertion exhibited growth defects and were sterile. DNA gel-blot hybridization and sequence analysis of the junction between the MRE11 cDNA and T-DNA insertion site confirmed that mre11-3 line had disruption in the conserved 5' end of the MRE11 gene, whereas the mre11-4 line had disruption within the less conserved 3' end. Expression analysis of the MRE11 gene in by semiquantitative RT-PCR demonstrated absence of the full-length mRNA species in both mutants. Although morphological defects seemed to be less severe in mre11-4, both mutants had similar abnormalities in meiosis: absence of chromosome pairing in the initial stages of meiosis and massive genome fragmentation, which was evident immediatelly after the leptotene stage. In spite of that, meiosis in both mutants progressed till the end and resulted in the formation of polyads containing microspores with unequal amounts of DNA. The chromosome fragmentation was substantially supressed and partially rescued in double mre11spo11-1 mutants. In contrast to yeast, where Mre11 is required for both induction of the Spo11-dependant DSBs and their repair, our results indicate that in Arabidopis Mre 11 is required for repair but not for the induction of meiotic DNA breaks.

Mre11; MRX complex; meiosis; meiotic double strand breaks; DNA repair; homologous secombination

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