| A deletion analysis of the regulatory region of the Arabidopsis floral homeotic gene APETALA3 ( AP3) has revealed that, like many cis-regulatory systems, the AP3 cis-regulatory system is modular in nature. Subsequent analysis of genes and proteins which interact with this cis-regulatory system has lead the proposal of a model for the early regulation of AP3. There appear to be three regions which are important for the initial activation of AP3 the proximal early element (PEE), the distal early element (DEE), and the AP3 minimal promoter region. The PEE is also required to maintain expression in the developing petals. Stamen specific expression is conferred by two modules, one which overlaps with and extends beyond the PEE and a second positioned between the PEE and DEE. Sequences contained within the PEE and the upstream region required to maintain expression in the developing stamens are capable of binding MADS box transcription factors, suggesting one or more MADS box proteins are required for appropriate AP3 expression. The AP3 minimal promoter region is required for early expression and contains putative GAGA factor binding sites, suggesting that this region may be subject to chromatin modification to allow for the activation of AP3. The PEE and DEE interact synergistically and respond to the floral meristem identity genes LFY and UFO. Furthermore, LFY is capable of binding to sequences within the DEE as well as to its co-regulator UFO. These data suggest that LFY and UFO are part of a protein complex which binds the DEE and PEE or they participate in recruiting the general transcriptional machinery in cooperation with proteins bound to the PEE. |
