A GENETIC SCREEN FOR MODIFIERS OF UFO MERISTEM ACTIVITY IDENTIFIES 3 NOVEL FUSED FLORAL ORGANS GENES REQUIRED FOR EARLY FLOWER DEVELOPMENT IN ARABIDOPSIS

In a screen to identify novel genes required for early Arabidopsis flo wer development, we isolated four independent mutations that enhance t he Ufo phenotype toward the production of filamentous structures in pl ace of flowers. The mutants fall into three complementation groups, wh ich we have termed FUSED FLORAL ORGANS (FFO) loci. ffo mutants have sp ecific defects in floral organ separation and/or positioning; thus, th e FFO genes identify components of a boundary formation mechanism(s) a cting between developing floral organ primordia. FFO1 and FFO3 have sp ecific functions in cauline leaf/stem separation and in first-and thir d-whorl floral organ separation, with FFO3 likely acting to establish and FFO1 to maintain floral organ boundaries. FFO2 acts at early flora l stages to regulate floral organ number and positioning and to contro l organ separation within and between whorls. Plants doubly mutant for two ffo alleles display additive phenotypes, indicating that the FFO genes may act in separate pathways. Plants doubly mutant for an ffo ge ne and for ufo, lfy, or clv3 reveal that the FFO genes play roles rela ted to those of UFO and LFY in floral meristem initiation and that FFO 2 and FFO3 may act to control cell proliferation late in inflorescence development.