Structure and Expression of OsMREII in Rice

摘要

In yeast and human cells, the Mre11 complex, which consists of Mre1; 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 afull-length cDNA clone, pOsMre1; encoding a rice ortholog of the Mrell protein. Its predicted protein sequence (M_r = 79.2 kDa and pl value = 5.91) contains a metallo-phosphoesterase domain at its N-ter-minal 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, aswell 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 bythe latter. RNA gel blot analysis showed that the level of OsMREII mRNA remained unchanged during the 1- to 4-d incubation period with MMS. In contrast, OsMREH 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 OsMREII gene. Based on these results, we discuss the possible functions of the OsMrett protein in a mechanism by which the stability of rice chromosomes is maintained.