Data from: The origin of floral organ identity quartets

The origin of flowers has puzzled plant biologists ever since Darwin
referred to their sudden appearance in the fossil record as an abominable
mystery. Flowers are considered to be an assembly of protective,
attractive and reproductive male and female leaf-like organs. Their origin
cannot be understood by a morphological comparison to gymnosperms, their
closest relatives, which develop separate male or female cones. Despite
these morphological differences, gymnosperms and angiosperms possess a
similar genetic toolbox consisting of phylogenetically related MADS-domain
proteins. Using ancestral MADS-domain protein reconstruction, we trace the
evolution of organ identity quartets along the stem lineage of crown
angiosperms. We provide evidence that current floral quartets specifying
male organ identity, which consist of four types of subunits, evolved from
ancestral complexes of two types of subunits through gene duplication and
integration of SEPALLATA proteins just before the origin of flowering
plants. Our results suggest that protein interaction changes underlying
this compositional shift were the result of a gradual and reversible
evolutionary trajectory. Modelling shows that such compositional changes
may have facilitated the evolution of the perfect, bisexual flower.