Fig. 4.

Model of A and C class gene antagonism. The negative regulation of class A gene activity in the inner two whorls is conferred by the post-transcriptional downregulation of AP2 by miR172 (a) and by the transcriptional repression of AP1 by AG (b). By contrast, the negative regulation of the class C gene AG in the outer two whorls depends on the LUG/SEU co-repressors recruited by the AP1/SEP MADS box proteins (c). The repression of miR172 also requires LUG/SEU and is mediated by AP2 (d). The dashed line represents a less well understood regulatory interaction between AG and AP2. Also indicated are the transcriptional activation of AG by LEAFY (LFY) and WUSCHEL (WUS) (Lohmann et al., 2001) and the activation of miR172 by SQUAMOSA PROMOTER BINDING PROTEIN-LIKE (SPL) (Wu et al., 2009).