Competence to Respond to Floral Inductive Signals Requires the Homeobox Genes PENNYWISE and POUND-FOOLISH

The transition from vegetative to reproductive development establishes new growth patterns required for flowering. This switch is controlled by environmental and/or intrinsic developmental cues that converge at the shoot apical meristem (SAM) [1–4]. During this developmental transition, floral inductive signals cause the vegetative meristem to undergo morphological changes that are essential for flowering [5, 6]. Arabidopsis plants containing null mutations in two paralogous BEL1 -like ( BELL ) homeobox genes, PENNYWISE ( PNY ) and POUND-FOOLISH ( PNF ), disrupt the transition from vegetative to reproductive development. These double mutants are completely unable to flower even though the SAM displays morphological and molecular changes that are consistent with having received floral inductive signals. These studies establish a link between the competence to receive floral inductive signals and restructuring of the SAM during floral evocation.