MADS-box gene evolution-structure and transcription patterns

This study presents a phylogenetic analysis of 198 MADS-box genes based on 420 parsimony-informative characters. The analysis includes only MIKC genes; therefore several genes from gymnosperms and pteridophytes are excluded. The strict consensus tree identifies all major monophyletic groups known from earlier analyses, and all major monophyletic groups are further supported by a common gene structure in exons 1-6 and by conserved C-terminal motifs. Transcription patterns are mapped on the tree to obtain an overview of MIKC gene transcription. Genes that are transcribed only in vegetative organs are located in the basal part of the tree, whereas genes involved in flower development have evolved later. As the universality of the ABC model has recently been questioned, special account is paid to the expression of A-, B-, and C-class genes. Mapping of transcription patterns on the phylogeny shows all three classes of MADS-box genes to be transcribed in the stamens and carpels. Thus the analysis does not support the ABC model as formulated at present.