MADS-box genes controlling flower development in rice

The separation between monocot and dicot plants occurred about 120-180 million years ago and since then major morphological changes have led to the striking differences that can be observed today. To understand whether, despite these differences, the processes controlling flower development are fundamentally comparable in dicot and monocot species, it is necessary to perform comparative studies. However, until recently flower development has been studied mainly in dicot plant species. Genetic and molecular analyses of two dicot model species, Arabidopsis thaliana and Antirrhinum majus, led to the formulation of the ABC model of flower development that describes how the combined activities of three classes of genes are required to drive flower organ development. This model has recently been extended by the inclusion of two other gene classes, namely D and E, which are involved in ovule development, and petal, stamen and carpel development, respectively. Most of the A, B, C, D and E genes identified so far have been shown to encode MADS-box transcription factors. In rice a number of regulatory genes belonging to the MADS-box transcription factor family have been cloned in the last few years and the functions of some of them have been investigated in detail. Here we review the current state of knowledge on rice flower development and focus on MADS-box genes that determine floral organ identity in this species. We compare results obtained in rice with the information known for Arabidopsis and the differences between these two species are discussed.