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. Sequencing
of (almost) the complete Arabidopsis genome enabled the identification of (almost)
all of the Arabidopsis MADS-box genes. MADS-box genes have been divided in two large
groups, termed type I and type II genes. The type II genes comprise the MEF2-like
genes of animals and fungi and the MIKC-type genes of plants. The majority of MIKC-type
genes are of the MIKC(c)-type, which includes all plant MADS-box genes for which expression
patterns or mutant phenotypes are known. By phylogeny reconstruction, almost all of
the MIKC(c)-type genes can be subdivided into 12 major gene clades, each clade comprising
1-6 paralogs from Arabidopsis and putative orthologs from other seed plants. Here
we first briefly describe the deep branching of the MADS-box gene tree to place the
MIKC(c)-type genes into an evolutionary context. For every clade of MIKC(c)-type genes
we then review what is known about its members from Arabidopsis and well-studied members
from other phylogenetically informative plant species. By gene sampling and phylogeny
reconstructions we provide minimal estimates for the ages of the different clades.
It turns out that 7 of the 12 major gene clades, i.e., AG-, AGL6-, AGL12-, DEF+GLO-
(B), GGM13- (B(s)), STMADS11- and TM3-like genes very likely existed already in the
most recent common ancestor of angiosperms and gymnosperms about 300MYA. Three of
the other clades, i.e., AGL2-, AGL17-, and SQUA-like genes, existed at least already
in the most recent common ancestor of monocots and eudicots about 200 MYA. Only for
two gene clades, AGL15-like genes (2 genes in Arabidopsis) and FLC-like genes (6 genes)
members from plants other than Brassicaceae have not been reported yet. Similarly,
only one ancient clade known from other flowering plant species, TM8-like genes, is
not represented in Arabidopsis. These findings reveal that the diversity of MADS-box
genes in Arabidopsis is rather ancient and representative for other flowering plants.
Our studies may thus help to predict the set of MADS-box genes in all other flowering
plants, except for relatively young paralogs. For the different gene clades we try
to identify ancestral and derived gene functions and review the importance of these
clades for seed plant development and evolution. We put special emphasis on gene clades
for which insights into their importance has rapidly increased just recently.