Separable Whorl-Specific Expression and Negative Regulation by Enhancer Elements within the AGAMOUS Second Intron

We analyzed the 4-kb intragenic control region of the AGAMOUS ( AG ) gene to gain insight into the mechanisms controlling its expression during early flower development. We identified three major expression patterns conferred by 19 AG ::reporter gene constructs: the normal AG pattern, a stamen-specific pattern, and a predominantly carpel pattern. To determine whether these three expression patterns were under negative control by APETALA2 ( AP2 ) or LEUNIG ( LUG ), we analyzed b -glucuronidase staining patterns in Arabidopsis plants homozygous for strong ap2 and lug mutations. Our results indicated that the stamen-specific pattern was independent of AP2 but dependent on LUG; conversely, the carpel-specific pattern was independent of LUG but dependent on AP2. These results lead to a model of control of AG expression such that expression in each of the two inner whorls is under independent positive and negative control.