Fig. 6.

Model summarizing three transitioning phases of Arabidopsis FM development: (A) phytomer establishment phase when the IM initiates discrete DRNL and DR5 expression foci at the periphery. Bract initiation establishes abaxial and adaxial polarity and there is interplay between the bract and the FM for founder cells. (B) The unidirectional phase during stage-1 and 2 that coincides with the absence of a stem cell population and the sequential and unidirectional initiation of sepals is dependent on PRESSED FLOWER function. Numbers show the order of sepal initiation for wild-type flowers (above) and lfy and puchi mutants (centre) and pan mutants (below). (C) The centripetal phase is associated with the re-establishment of a stem cell population in the FM centre from late stage-2, and initiation of petals, stamens, and carpels in concentric whorls (shown by the black circle with arrows).