PARALLELS BETWEEN UNUSUAL FLORAL ORGANS AND FIMBRIATA, GENES-CONTROLLING FLOWER DEVELOPMENT IN ARABIDOPSIS AND ANTIRRHINUM

The unusual floral organs (ufo) mutant of Arabidopsis has flowers with variable homeotic organ transformations and inflorescence-like charac teristics. To determine the relationship between UFO and previously ch aracterized meristem and organ identity genes, we cloned UFO and deter mined its expression pattern, The UFO gene shows extensive homology wi th FIMBRIATA (FIM), a gene mediating between meristem and organ identi ty genes in Antirrhinum. All three UFO mutant alleles that we sequence d are predicted to produce truncated proteins. UFO transcripts were fi rst detected in early floral meristems, before organ identity genes ha d been activated. At later developmental stages, UFO expression is res tricted to the junction between sepal and petal primordia. Phenotypic, genetic, and expression pattern comparisons between UFO and FIM sugge st that they are cognate homologs and play a similar role in mediating between meristem and organ identity genes, However, some differences in the functions and genetic interactions of UFO and FIM were apparent , indicating that changes in partially redundant pathways have occurre d during the evolutionary divergence of Arabidopsis and Antirrhinum.