Fig. 5. A proposed model of how the inner whorl-specific activation of AG is achieved. In whorls 1 and 2, multiple negative regulatory activities impinge upon the AG cis-regulatory region (such as the AG intron II) to prevent AG transcription. These negative regulatory factors include AP2, BLR and SEU/LUG/AP1 or SEU/LUG/SEP3. In whorls 3 and 4, multiple positive regulatory factors antagonize the negative effect of SEU/LUG/SEP3 to promote AG transcription. These positive regulatory factors include the combined activities of LFY and WUS, as well as positive autoregulation by AG/SEP3. Additionally, the AG/SEP3 complex inhibits AP1 transcription and an interaction between AG and SEP3 may preclude the SEU/LUG co-repressors from interacting with SEP3. Arrows leading from AP1 or SEP3 to respective LUG/SEU/AP1, LUG/SEU/SEP3 or AG/SEP3 complexes indicate the incorporation of these MADS box proteins into the respective protein complexes.