GENETIC AND PHYSICAL MAPPING IN BRASSICA DIPLOID SPECIES OF A GENE-CLUSTER DEFINED IN ARABIDOPSIS-THALIANA

We report the genetic and physical analysis by pulse field gel electro phoresis (PFGE) in three Brassica diploid genomes for a cluster of fiv e genes characterized in a selected segment of 15 kb on chromosome 3 o f Arabidopsis thaliana, encoding a Bradyrhizobium CycJ homologue (Atl) , a rat p67 translation factor homologue (At2), an Em-like (early meth ionine) protein (At3), chlorophyll synthase (At4) and a yeast Sad homo logue (A5). The Arabidopsis gene array was found to be conserved on a single linkage group in each of the Brassica genomes. However, partial complexes were found to be duplicated in other chromosome segments on the same or other linkage groups. Some of the At genes, which could n ot be genetically mapped because of lack of polymorphism, were assigne d to their respective linkage groups by physical mapping. The presence of multiple copies of the A. thaliana gene cluster in the three Brass ica genomes further establishes their complex nature, which results fr om extensive duplication and chromosomal rearrangement. In general, ge netic distances between the At genes agreed with values expected for t he physical distances determined in Brassica.