Summary
Flowering and reversion in Impatiens are characterised by gradual transitions of organ identity and constitute a unique system for the molecular and physiological study of floral organogenesis. The authors have isolated an Impatiens homologue of the FIM gene of Antirrhinum (UFO in Arabidopsis), ImpโFIM, and analysed its expression in three states of the terminal meristem: vegetative, floral, and reverted. In floral meristems, ImpโFIM transcription is associated with petal identity, as in Antirrhinum and Arabidopsis, but this is achieved through a novel transcription pattern, characterised by a high level of transcript within petal primordia. This novel transcription pattern could contribute to the more diffuse boundaries between organ types in Impatiens. In vegetative meristems, ImpโFIM is expressed in the axils of leaf primordia which are arranged in a spiral. A similar pattern is observed in reverted meristems in which leaf primordia are initiated in a whorled arrangement. This result indicates that the maintenance of floral phyllotaxis is not associated with a specific pattern of ImpโFIM transcription. Transcription of ImpโFIM in a nonโreverting line is no different from that in the reverting line. Therefore, the lack of floral commitment in the reverting line does not seem to be responsible for ImpโFIM transcription within petals. The novel transcription pattern in petals, together with features of Impatiens that are reminiscent of fim and ufo mutant phenotypes suggest an evolutionary divergence for ImpโFIM regulation in this species.