Regulation of Flower Development in Arabidopsis by SCF Complexes

Abstract

SCF complexes are the largest and best studied family of E3 ubiquitin protein ligases that facilitate the ubiquitylation of proteins targeted for degradation. The SCF core components Skp1, Cul1, and Rbx1 serve in multiple SCF complexes involving different substrate-specific F-box proteins that are involved in diverse processes including cell cycle and development. In Arabidopsis, mutations in the F-box gene UNUSUAL FLORAL ORGANS (UFO) result in a number of defects in flower development. However, functions of the core components Cul1 and Rbx1 in flower development are poorly understood. In this study we analyzed floral phenotypes caused by altering function of Cul1 or Rbx1, as well as the effects of mutations in ASK1 and ASK2. Plants homozygous for a point mutation in the AtCUL1 gene showed reduced floral organ number and several defects in each of the four whorls. Similarly, plants with reduced AtRbx1 expression due to RNA interference also exhibited floral morphological defects. In addition, compared to the ask1 mutant, plants homozygous for ask1 and heterozygous for ask2 displayed enhanced reduction of B function, as well as other novel defects of flower development, including carpelloid sepals and an inhibition of petal development. Genetic analyses demonstrate that AGAMOUS (AG) is required for the novel phenotypes observed in the first and second whorls. Furthermore, the genetic interaction between UFO and AtCUL1 supports the idea that UFO regulates multiple aspects of flower development as a part of SCF complexes. These results suggest that SCF complexes regulate several aspects of floral development in Arabidopsis.An Arabidopsis flower has four concentric whorls that contain four sepals, four petals, six stamens, and two carpels. After the transition from vegetative to reproductive development, the Arabidopsis apical meristem (inflorescence meristem) produces the floral meristem, which in turn undergoes a series of developmental stages to form a flower (Smyth et al., 1990). Genetic and molecular studies have uncovered a large number of genes that control different steps in flower development including flowering time, flower meristem identity, and flower organ identity (Zhao et al., 2001a). In particular, the ABC model has been proposed for the specification of floral organ identity (Coen and Meyerowitz, 1991;Ma, 1994;Weigel and Meyerowitz, 1994;Ma and dePamphilis, 2000). The combinatorial expression of ABC genes defines the organ type that differentiates in each whorl: A function alone specifies the sepal identity; A and B function together controls petal identity; B and C function together specifies stamen identity; and C function alone directs carpel identity.The UNUSUAL FLORAL ORGANS (UFO) gene is involved in multiple aspects of floral development, including regulating floral meristem identity and floral organ development (Levin and Meyerowitz, 1995;Wilkinson and Haughn, 1995). One known function of UFO in floral organ development is a positive regulation of the expression of B function gene APETALA3 (A...

The poetry of reproduction: the role of LEAFY in Arabidopsis thaliana flower formation

“…UFO is an F-box protein (Ingram et al, 1995;Samach et al, 1999). F-box proteins form part of SCF ubiquitin ligase complexes that polyubiquitinate proteins, targeting them for destruction via the 26S proteasome (Sullivan et al, 2003;Wang et al, 2003;Ni et al, 2004). UFO has been shown to interact with components of SCF complexes and these complex members function in flower development (Samach et al, 1999;Zhao et al, 1999;Wang et al, 2003;Ni et al, 2004) and regulate B class gene expression (Zhao et al, 2001).…”

Patterning of Inflorescences and Flowers by the F-Box Protein DOUBLE TOP and the LEAFY Homolog ABERRANT LEAF AND FLOWER of Petunia

“…Genetic and biochemical evidence indicates that UFO operates as part of an SCF complex that is associated with the COP9 signalosome (Zhao et al, 2001;Wang et al, 2003;Ni et al, 2004). SCF complexes are ubiquitin ligases that bind their substrate via F-box proteins (Patton et al, 1998).…”

Regulation of Arabidopsis tapetum development and function by DYSFUNCTIONAL TAPETUM1 (DYT1) encoding a putative bHLH transcription factor

“…The primers for real-time PCR are listed in Tables 1 and 3. The PCR and data treatment were carried out as described previously (Ni et al, 2004). Plant tissue was collected and quickly frozen in liquid nitrogen.…”