Cell-cell signaling and movement by the floral transcription factors LEAFY and APETALA1.

LEAFY (LFY) and APETALA1 (AP1) encode unrelated transcription factors that activate overlapping sets of homeotic genes in Arabidopsis flowers. Sector analysis and targeted expression in transgenic plants were used to study whether LFY and AP1 can participate in cell-cell signaling between and within different layers of the floral meristem. LFY signaled equally well from all layers and had substantial long-range action within layers. Nonautonomous action of LFY was accompanied by movement of the protein to adjacent cells, where it directly activated homeotic target genes. In contrast, AP1 had only limited nonautonomous effects, apparently mediated by downstream genes because activation of early target genes by AP1 was cell-autonomous.