CHARACTERIZATION OF THREE MISMATCH REPAIR GENES IN ARABIDOPSIS

Pavillon Charles-Eugene Marchand, Universite Laval, Quebec, Canada, G1K 7P4

Wild germplasm represents a rich reservoir of useful genes which can be introgressed into cultivated species through traditional plant breeding methods. These efforts are, however, frequently impaired by the low rate of recombination encountered in wide crosses. It has been proposed that the cellular DNA mismatch repair (MMR) system intervenes and interrupts recombination events involving homeologous chromosomes when sequence divergence leads to mismatched bases. We have recently cloned three key mismatch repair genes in Arabidopsis thaliana: AtMSH2, AtMLH1 and AtPMS1. All three show extensive sequence homology with their eukaryotic counterparts, thus suggesting a similarity in function. In view of facilitating interspecific exchanges, we have initiated a research program aimed at deciphering the role of these genes in DNA mismatch repair, recombination and genome stability. Both biochemical and genetic studies are being carried out to assess the function of these genes. We find that the AtMSH2 protein (overexpressed in E.coli) shows a 10X greater affinity for DNA containing a mismatch, an observation consistent with its presumed role in DNA mismatch repair. Genetic analyses have focused on the isolation of insertional mutants (see also poster by Pelletier et al., this meeting) and the production of antisense calli/plants to probe the functions of these genes. The calli and plants analysed so far have failed to show microsatellite instability, a phenotype expected in MMR-deficient lines. More detailed analyses of these and other lines are currently in progress.