Function and evolution of the plant MADS-box gene family

The function of MADS-box genes in flower and fruit development has been uncovered at a rapid pace over the past decade. Evolutionary biologists can now analyse the expression pattern of MADS-box genes during the development of different plant species, and study the homology of body parts and the evolution of body plans. These studies have shown that floral development is conserved among divergent species, and indicate that the basic mechanism of floral patterning might have evolved in an ancient flowering plant. Key Points Members of the MADS-box family of developmental genes have been found in plants, animals and fungi, with plants having by far the largest number. Two types of MADS-box gene (type I and type II) have been identified on the basis of the amino-acid sequences in the MADS-box domain. Only type II MADS-box genes have been analysed at the functional level. MADS-box genes have a wide range of functions, in the formation of flowers, the control of flowering time and the control of vegetative development. The landmark ABC model of flower organ identity states that three classes of homeotic gene, most of which encode MADS-box proteins, function in a combinatorial manner to specify regional identities in the four floral whorls. Orthologous genes in different plant species have analogous functions, indicating that the underlying mechanisms that control development might be widely conserved and that MADS-box genes have had a crucial function in plant evolution. The mechanism used to pattern the flower is conserved between distantly related flowering plants such as Arabidopsis and maize and might have evolved before the divergence of monocots and eudicots. The analysis of MADS-box genes in further plant species will help to uncover the role of these important genes in morphological evolution.