The Arabidopsis floral homeotic gene APETALA3 differentially regulates intercellular signaling required for petal and stamen development

Cell-cell signaling is crucial for the coordination of cell division and di fferentiation during plant organogenesis. We have developed a novel mosaic analysis method for Arabidopsis, based on the maize Ac/Ds transposable elem ent system, to assess the requirements of individual genes in intercellular signaling. Using this strategy, we have shown that the floral homeotic APE TALA3 (AP3) gene has distinct roles in regulating intercellular signaling i n different tissues. In petals, AP3 acts primarily in a cell-autonomous fas hion to regulate cell type differentiation, but its function is also requir ed in a non-cell-autonomous fashion to regulate organ shape. In contrast, A P3-regulated intercellular interactions are required for conferring both ce ll type identity and organ shape and size in the stamens. Using antibodies raised against AP3, we have shown that the AP3 protein does not traffic bet ween cells. These observations imply that AP3 acts by differentially regula ting the production of intercellular signals in a whorl-specific manner.