SATURATING THE GENETIC-MAP OF ARABIDOPSIS-THALIANA WITH EMBRYONIC MUTATIONS

One goal of the Arabidopsis genome project is to identify every gene with an essential function in growth and development. Towards that end, the results are reported here of a mapping project designed to enhance the linkage map of Arabidopsis and establish a valuable resource of mutations in essential genes with known map locations. Embryo-defective (emb) mutations were chosen because they represent the most common heritable defect identified following mutagenesis in Arabidopsis. Multiple marker lines with easily scored phenotypes were con structed to facilitate mapping efforts. Recombination data were obtained for 169 mutants defective in embryogenesis. The chromosomal locations of 110 emb genes are presented in this report. Twenty-six of these genes are tagged with T-DNA. Nine other mutants isolated following seed transformation appear to contain chromosomal translocations. Another 31 mutant genes in the collection have been assigned to a linkage group but not yet placed on the map. Nineteen examples of duplicate alleles have also been found. This is consistent with the estimate that approximately 500 genes readily mutate to give an embryo defective phenotype in Arabidopsis. With continued progress, it may therefore be possible to approach saturation for this important class of mutations. Molecular cloning of these genes should be facilitated by identifying cDNAs and genomic sequences that map to similar locations.