The almost complete sequence from the Arabidopsis genome has been available for the last few months. We investigated the position of a number of members of multigene families and observed that the Arabidopsis genome is made of a patchwork of large duplicated chromosomal fragments. This raised the question of a possible polyploid origin of this suposedly simple genome. Comparing the sequence of duplicated genes in Arabidopsis with their Brassica orthologues suggested that the major duplications predate the differenciation of Arabidopsis from Brassica and occured about 30-35 MY ago.
Among the genes which were investigated are the ribosomal protein genes. We identified the whole set of 249 genes or pseudo genes coding for 80 proteins. We found that most of them are transcribed and expressed, but usually differentially, depending on the developmental stage. We also investigate the presence of snoRNA genes which are involved in the processing of rRNA precursors and found several situations in which these genes are encoded into introns of ribosomal proteins or other proteins involved in nucleolar morphogenesis . The observation of a number of duplications in Arabidopsis led us, with several colleagues belonging to the EuDicotMap European consortium, to investigate their occurrence in other major crops. Large duplications, some of which correspond to those in Arabidopsis, were observed in sugar beet, potato, sunflower and prunus. The evolutionary implications of these findings will be discussed.