UNUSUAL FLORAL ORGANS CONTROLS MERISTEM IDENTITY AND ORGAN PRIMORDIA FATE IN ARABIDOPSIS

A novel gene that is involved in regulating flower initiation and deve lopment has been identified in Arabidopsis. This gene has been designa ted UNUSUAL FLORAL ORGANS (UFO), with five corresponding nuclear reces sive alleles designated ufo-1 to ufo-5. Under short day-length conditi ons, ufo homozygotes generate more coflorescences than do the wild typ e, and coflorescences often appear apical to the first floral shoot, r esulting in a period of inflorescence development in which regions of floral and coflorescence shoots are produced alternately. ufo enhances the phenotype of weak leafy alleles, and the double mutant Ufo-1 Apet ala1-1 produces only coflorescence-like shoots, suggesting that these two genes control different aspects of floral initiation. Floral devel opment was also altered in Ufo plants. Ufo flowers have an altered org an number in all whorls, and organs in the first, second, and third wh orls exhibit variable homeotic transformations. Ufo single and double mutant phenotypes suggest that the floral changes result from reductio n in class B floral homeotic gene expression and fluctuations in the e xpression boundaries of class C function and FLO10. Surprisingly, in s itu hybridization analysis revealed no obvious differences in expressi on pattern or level in developing Ufo flowers compared with that of th e wild type for any class B or C gene studied. We propose that UFO act s in concert with known floral initiation genes and regulates the doma ins of floral homeotic gene function.