Figure 5.

Genetic Model for Floral Organ Identity Determination in Rice.

The existence of a true rice A function determining the identity of the first- and second-whorl organs has, like in most flowering plants, not been identified yet. The homeotic conversion of the carpel into a palea-like organ in the mads3 mads58 double mutant suggests that only the palea, and not the lemma, can be considered as a first-whorl organ. The class B genes regulate lodicule identity in the second whorl, and together with class C genes, they determine stamen identity in the third whorl. In the fourth whorl, DL represses the expression of class B genes. The main class C genes of rice are MADS3 and MADS58. Since the ovule develops directly from the FM, it can be considered a fifth-whorl organ. Based on current data, MADS13 seems to be the only AG subfamily gene regulating ovule identity in rice. Among the four AG subfamily genes of rice, MADS3, MADS13, and MADS58 regulate also FM determinacy, whereas MADS21 seems not to play important functions during flower development. The MADS domain proteins shown in this model might interact with SEP-like and/or AGL6-like MADS domain proteins providing E-function (Favaro et al., 2002; Kater et al., 2006; Ohmori et al., 2009; Cui et al., 2010; Li et al., 2010; Li et al., 2011a), which for simplicity are not shown in this scheme.