MADS-box genes reveal that gnetophytes are more closely related to conifers than to flowering plants

The evolutionary origin of the angiosperms (flowering plants sensu stricto) is still enigmatic. Answers to the question of angiosperm origins are inti mately connected to the identification of their sister group among extinct and extant taxa.,Most phylogenetic analyses based on morphological data agr ee that among the groups of extant seed plants, the gnetophytes are the sis ter group of the angiosperms. According to this view, angiosperms and gneto phytes are the only extant members of a clade called "anthophytes" to empha size their shared possession of flower-like reproductive structures. Howeve r, most phylogeny reconstructions based on molecular data so far did not su pport an anthophyte clade, but also could not clarify the case because supp ort for alternative groupings has been weak or controversial. We hale isola ted 13 different homologs of MADS-type floral homeotic genes from the gneto phyte Gnetum gnemon. Five of these genes fall into monophyletic gene clades also comprising putatively orthologous genes from flowering plants and con ifers, among them orthologs of floral homeotic B and C function genes. with in these clades the Gnetum genes always form distinct subclades together wi th the respective conifer genes, to the exclusion of the angiosperm genes. This provides strong molecular evidence for a sister-group relationship bet ween gnetophytes and conifers, which is in contradiction to widely accepted interpretations of morphological data for almost a century, Our phylogeny reconstructions and the outcome of expression studies suggest that complex features such as flower-like reproductive structures and double-fertilizati on arose independently in gnetophytes and angiosperms.