Structure and expression of OsMRE11 in rice

In yeast and human cells, the Mre11 complex, which consists of Mre11, Rad50, and Xrs2/Nbs1 proteins, participates in basic aspects of chromosome metabolism, such as the repair of meiotic DNA breaks and telomere maintenance. In this study, we isolated a full-length cDNA clone, pOsMre11, encoding a rice ortholog of the Mre11 protein. Its predicted protein sequence (M_r = 79.2 kDa and pl value = 5.91) contains a metallo-phosphoesterase domain at its N-terminal region, and a single putative DNA binding domain in the central region of the protein, with significant homology to corresponding motifs in human and yeast Mre11 proteins. The OsMRE11 gene is constitutively expressed in all tissues examined here, including leaves, roots, tillers, and meristems, as well as in undifferentiated callus cells. When 10-d-old rice seedlings were treated with 0.025% methyl methanesulfonate (MMS) or 30 watts of UV-C light, they were apparently damaged by those genotoxic agents, with plants being more seriously injured by the latter. RNA gel blot analysis showed that the level of OsMRE11 mRNA remained unchanged during the 1- to 4-d incubation period with MMS. In contrast, OsMRE11 expression appeared to increase after 3 d of irradiation. In addition, treatments with salicylic acid and jasmonic acid, two important defense-related hormones, significantly activated the OsMRE11 gene. Based on these results, we discuss the possible functions of the OsMre11 protein in a mechanism by which the stability of rice chromosomes is maintained.