Disruption of the Arabidopsis RAD50 gene leads to plant sterility and MMS sensitivity

The Rad50 protein is involved in the cellular response to DNA-double strand breaks (DSBs), including the detection of damage, activation of cell-cycle checkpoints, and DSB repair via recombination. It is essential for meiosis in yeast, is involved in telomere maintenance, and is essential for cellul ar viability in mice. Here we present the isolation, sequence and character ization of the Arabidopsis thaliana RAD50 homologue (AtRAD50) and an Arabid opsis mutant of this gene. A single copy of this gene is present in the Ara bidopsis genome, located on chromosome II. Northern analysis shows a single 4.3 Kb mRNA species in all plant tissues tested, which is strongly enriche d in flowers and other tissues with many dividing cells. The predicted prot ein presents strong conservation with the other known Rad50 homologues of t he amino- and carboxy-terminal regions. Mutant plants present a sterility p henotype which co-segregates with the T-DNA insertion. Molecular analysis o f the mutant plants shows that the sterility phenotype is present only in t he plants homozygous for the T-DNA insertion. An in vitro mutant cell line, derived from the mutant plant, shows a clear hypersensitivity to the DNA-d amaging agent methylmethane sulphonate, suggesting a role of RAD50 in doubl e-strand break repair in plant cells. This is the first report of a plant m utated in a protein of the Rad50-Mre11-Xrs2 complex, as well as the first d ata suggesting the involvement of the Rad50 homologue protein in meiosis an d DNA repair in plants.