Fig. 3. AP1 and SEP3 mediate the repressor activity of SEU/LUG. (A) AP1-BD and SEP3-BD, with GAL4 BD at the N terminus of the fusion proteins, mediate the repressor activity of SEU/LUG in yeast, as indicated by the ß-galactosidase activity from the GAL7-lacZ reporter. AP1-BD (lane 3) and SEP3-BD (lane 9), but not BD (pGBT9 vector; lanes 1-2), activate lacZ expression. This activity is reduced in the presence of SEU (lanes 4, 10). Full-length LUG (lanes 5, 6, 11, 12) and LUG without its LUFS domain (LUG_deltaLUFS; lanes 7, 8, 13, 14) were tested in the presence or absence of SEU. Error bars show the standard deviation of means of triplicate assays. (B) Diagram of the pAG3'I::LUC reporter. An 900 bp fragment from the 3' AG enhancer is inserted upstream of the TATA box of the 35S promoter that drives firefly luciferase (LUC). The two LFY/WUS-binding sites (black circles) and the two CArG boxes (diamonds) are indicated. (C) AP1 and SEP3 mediate the repression of the pAG3'I::LUC reporter in onion cells. The ratio of pAG3'I::LUC and 35S::Renilla LUC expression is shown. Onion epidermal cells were transiently transformed with 35S::AP1 or 35S::SEP3, together with 35S::SEU or 35S::LUG, or 35S::SEU plus 35S::LUG. The pART7 vector was a negative control. Error bars show standard deviation of means of triplicate assays.