Growth and development of AtMSH7 mutants in Arabidopsis thaliana

DNA mismatch repair (MMR) is a highly conserved biological pathway that improves the fidelity of DNA replication and recombination. MMR is initiated when MutS proteins recognize mismatches and small loops of unpaired nucleotides. Arabidopsis thaliana and other plants encode MutS protein homologs (MSH) conserved among other eukaryotic organisms, but also encode an extra MSH polypeptide (MSH7). In order to better understand the role of MSH7 in vivo, a full set of phenotypic parameters that covered the development of the plant from seed imbibition to flowering and seed maturation was analyzed in A. thaliana harboring two different msh7 alleles. Plants deficient in MSH7 show statistically significant faster germination rates, longer primary roots during the juvenile vegetative phase, and higher cauline leaf and axillary and lateral inflorescence numbers compared with wild type. We also quantified number, length and area of siliques and seed number per silique. Disruption of MSH7 resulted in a higher number of smaller siliques than wild type. There were no differences in seed number per silique between genotypes. These findings suggest that mutant plant growth appears to be caused by an impaired cell cycle checkpoint that allows cell division without adequate DNA repair. This increase in proliferation activity demonstrates a functional and temporal link between DNA repair and cell cycle regulation.