MADS‐BOX GENES: DEVELOPMENT AND EVOLUTION OF PLANT BODY PLANS

We review functional data on MADS‐box genes, recent phylogenetic analyses of these coding regions, and their roles in the development and evolution of key morphological innovations in plants. We map the origin of important morphological structures in particular diverse stages of the life cycle in different plant clades onto organismal phylogenies, and present relevant molecular genetic aspects of development related to the MADS‐box genes. We focus on reproductive structures of the sporophyte because most functional characterizations have been done of MADS‐box genes involved in flower development. We discuss MADS‐box evolution in flowering plants, but we also review studies in the other nonflowering vascular plants, gymnosperms (conifers and gnetales), and ferns and preliminary data from the algae. We suggest that floral (e.g. flowering time, inflorescence, and flower meristem identity) MADS‐box and nonfloral plant MADS‐box genes should be the focus of future comparative research. Cloning and functional analyses of MADS‐box genes in bryophytes, particularly in the experimental system Physcomitrella patens (Hedw.) B.S.G., are needed. The ABC model of floral organ specification is an excellent general representation of an important network of genes; however, formal analytical tools are required to integrate data on complex gene interaction in comparative analyses. This and other analytical approaches to constructing gene network models will help to frame homology hypotheses in an evolutionary and developmental framework.