Transcription pattern of a FIM homologue in Impatiens during floral development and reversion

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), Imp-FIM, and analysed its expression in three states of the terminal meristem: vegetative, floral, and reverted. In floral meristems, Imp-FIM 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, Imp-FIM 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 Imp-FIM transcription. Transcription of Imp-FIM in a non-reverting 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 Imp-FIM 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 Imp-FIM regulation in this species.