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Major life cycle transitions happen after changes in stem cells trigger new developmental programs. In moss, expression of the homeobox transcription factor BELL1 is sufficient to induce sporophyte stem cells from the gametophyte phase, without having to go through fertilization.
Angiosperm evolution involves a major transition from spiral to whorled arrangements of floral organs. Examination of the genetic programs specifying floral organ identity in Nigella damascene, a species of Ranunculaceae with spiral flowers, illuminates the molecular basis of how spiral flowers can have flexible numbers of floral organs.
