MADS-box genes in the evolution of vascular plants

Here you can see a simple tree of major taxa of vascular plants. The time scale (in MYA, i.e. million years ago) given at the nodes of the tree are rough (and in part controversal) estimations based on different studies.
The topology of the tree is also controversial: that Gnetales are more closely related to conifers than to angiosperms could be concluded from some of our studies on MADS-box genes in these taxa (Winter et al. unpublished data), but is in contrast to textbook interpretations of morphological data.
Three important stages in the evolution of the megasporangium are depicted schematically at the left side of the root at the three lower internal branches. From bottom to top: no integuments are covering the sporangium, a condition still found in extant ferns; a sporangium surrounded by an integument (ovule); and a sporangium covered by a carpel.
The gene names besides the branches denote gene subfamilies, not single genes. These have been established at the latest during the time interval represented by the respective branches of the phylogenetic tree. This could be concluded from the presence of respective subfamily members in extant taxa. For example, AG-, AGL2-, AGL6-, DEF/GLO-, GGM13- and TM3-like genes have already been isolated from angiosperms and gymnosperms, but not from ferns. At the root of the phylogenetic tree, the domain structure of a typical MIKC-type MADS-box gene is shown. Our analyzes have demonstrated that the last common ancestor of ferns and seed plants had already at least two genes of that type.

Abbreviations of genes and gene subfamilies:

-AG: AGAMOUS

-AGL2,6,12,15,17: AGAMOUS-like gene No. 2,6,12,15,17

-CRM1,3,6,7: Ceratopteris richardii MADS-box gene No. 1,3,6,7

-DEF: DEFICIENS

-GGM4-7,10,13: Gnetum gnemon MADS-box gene No. 4-7,10,13

-GLO: GLOBOSA

-SQUA: SQUAMOSA

-TM3,8: Tomato MADS-box gene No. 3,8

home for questions and remarks please send e-mails to abecker@mpiz-koeln.mpg.de