Functional Characterization Of Arabidopsis DNA Mismatch Repair Protein MSH5 During Meiosis

MSH is a group of MutS homolog protein. Homology-based search has revealed seven MutS homologs, designated AtMSH1-7, in eukaryotic cells. MSH5, a member of MutS homolog DNA mismatch repair protein family, has been demonstrated to be required for proper homologous chromosome recombination in diverse organisms such as mouse, budding yeast and C.elegans. In this study, we show that Arabidopsis atmsh5 mutants isolated from the SALK T-DNA insertion mutant collection exhibits normal vegetative growth but severe reduction in fertility. For example, the length of the atmsh5 mutant silique is only 50% of that in wild type; accordingly the seed-set of atmsh5 mutant is only 10% of that in wild type. The seed-set of atmsh5-2/atmsh5-2 and atmsh5-3/atmsh5-3 are about 4.8±1.0(n=62) and 4.9±0.9(n=56), respectively. The results of pollen staining with Alexander's solution and CLSM indicate that 55% of pollen grains are non-viable and 85% of embryo sacs are abnormal due to the disruption of AtMSH5 gene. Cytological analysis with DAPI revealed defects in the meiocytes of atmsh5 mutant. It's found that there are numerous univalents at diakinesis present in the mutant, in contrast to five bivalents during corresponding meiotic stages in the wild-type meiocytes. To confirm the causal relationship between the phenotypes observed and the disruption of AtMSH5 gene, we further complemented the atmsh5 mutant with the full-length of CDS of AtMSH gene under the control of CaMV 35S promoter. The results showed that both the silique length and the seed-set of the mutants are the same as that of wild type, indicating a successful complementation of the mutant phenotypes. Taken together, AtMSH5 is very important during the meiosis in Arabidopsis.