MADS-box genes encode a family of transcription factors which control diverse developmental processes in flowering plants ranging from root to flower and fruit development. A large screening for MIKC-type MADS-box gene cDNAs in maize yielded sequences for 31 different genes, 29 of which are of the MIKC-type. 15 of these MIKC-type genes were novel. Together with three published genes for which a cDNA did not appear in our screen 32 different MIKC-type genes have thus been identified in maize now. All of these genes are members of subfamilies known from eudicots. However, it appears that in many subfamilies there are more gene members in maize than in eudicot model plants such as Arabidopsis. Phylogeny reconstructions involving all published MADS-box genes identified two major reasons for this. First, after the establishment of the defined gene subfamilies in a common ancestor of eudicots and monocots, a number of gene duplications occurred in the lineage that led to extant monocots after the eudicots had branched off, but before the separation of the lineages that led to extant maize and rice. Based on our gene collection we could estimate that there must have been at least 20 different MIKC-type genes in the most recent common ancestor of maize and rice about 50-70 million years ago. In contrast, the same data set supports only the presence of at least 11 different genes in the last common ancestor of monocots and eudicots about 200 million years ago. Second, phylogenetic trees in line with chromosomal mapping data revealed that the event that gave rise to the ancient segmental allotetraploidy of the maize genome established typically two young paralogs for many orthologous rice MADS-box genes. By chromosomal mapping also candidate genes for some interesting maize developmental gene loci could be identified. The genes reported here are a rich ressource for further studies on the evolutionary dynamics of a complex gene family, the developmental genetics of maize, and a rational crop design employing developmental control genes as tools.
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|Published - 2002