![]() Siblings from the F4 generation segregating for lfy-26 in the 35S::UFO-mychomozygous background were assessed for their phenotypes. Homozygotes for 35S::UFO-myc were selected in the F2 generation. For dose studies, lfy-26 homozygotes were crossed to homozygous 35S::UFO-myc plants. Plants were grown in 3:1 vermiculite: soil at 22☌ under 16-hour light/8-hour dark conditions. UFO is expressed in all shoot meristems in a dynamic pattern, but in the flower the expression domain of UFO largely coincides with that of AP3, providing regional specification( Lee et al., 1997 Long and Barton, 1998 Samach et al., 1999). Furthermore, ectopic expression of LFY and UFO together is sufficient to induce ectopic AP3 expression,while ectopic expression of LFY alone is insufficient( Lee et al., 1997 Parcy et al., 1998). Every aspect of this gain-of-function phenotype of UFO is abolished when LFY activity is absent, indicating that the function of UFOis dependent on LFY activity ( Lee et al., 1997). This gain-of-function phenotype of UFO in flowers is due to ectopic AP3 expression because the phenotype is completely abolished when functional AP3 is not present( Lee et al., 1997). Ectopic expression of UFO in plants containing a 35S::UFOtransgene results in a dramatic phenotype in which carpels are transformed to stamens, extra petals are formed and leaf margins are serrated( Lee et al., 1997). AP1 expression is initially activated throughout the flower in response to LFY activity ( Parcy et al.,1998 Wagner et al.,1999), and becomes confined to the first two floral whorls as a consequence of AG-mediated repression in the center of the meristem( Gustafson-Brown et al.,1994).īy contrast, the activation of AP3 expression in developing petal and stamen primordia requires the activity of the F-box protein UNUSUAL FLORAL ORGANS ( UFO) in conjunction with that of LFY( Ingram et al., 1995 Jack et al., 1992 Lee et al., 1997 Levin and Meyerowitz, 1995 Wilkinson and Haughn, 1995). AG is expressed in a restricted region consisting of the inner two floral whorls WUSCHEL (WUS), a homeodomain containing protein that is expressed in the center of the floral meristem, has been shown to directly activate AG in conjunction with LFY, resulting in localized expression( Lenhard et al., 2001 Lohmann et al., 2001). The spatially and temporally restricted transcriptional activation of both AP1 and AG depends on the concerted action of LFY in combination with other transcription factors. However, AP1, AP3 and AG are expressed in distinct spatial domains,while LFY is expressed throughout the floral meristem, implying that the mode of action of LFY in activating different classes of floral homeotic genes is distinct ( Parcy et al., 1998). LFY has been shown to bind to a loosely defined CC(A/T)(A/G)(G/T)G(G/T) consensus site in the regulatory regions of the APETALA1 ( AP1), APETALA3 ( AP3) and AGAMOUS ( AG) floral homeotic genes( Busch et al., 1999 Lamb et al., 2002 Lohmann et al., 2001 Parcy et al., 1998 Wagner et al., 1999). LFY encodes a novel plant-specific transcription factor, and its role in activating floral homeotic genes has been shown to be separable from that of conferring floral meristem identity ( Parcy et al., 1998). This mechanism may be widely conserved, as homologs of UFO and LFY have been identified in a wide array of plant species. These results suggest a novel mechanism for promoting flower development via protein degradation and concomitant activation of the LFY transcription factor. ![]() These results define an unexpected role for an F-box protein in functioning as a DNA-associated transcriptional co-factor in regulating floral homeotic gene expression. Moreover, chemical or genetic disruption of proteasome activity compromises LFY-dependent AP3 activation,indicating that protein degradation is required to promote LFY activity. Furthermore, a transcriptional repressor domain fused to UFO reduces endogenous LFY activity in plants, supporting the idea that UFO acts as part of a transcriptional complex at the AP3 promoter. Here, we show that UFO physically interacts with LFY both in vitro and in vivo, and this interaction is necessary to recruit UFO to the AP3 promoter. LFY-dependent activation of the homeotic APETALA3 ( AP3) gene requires the activity of UNUSUAL FLORAL ORGANS (UFO), an F-box component of an SCF ubiquitin ligase, yet how this regulation is effected has remained unclear. The Arabidopsis LEAFY (LFY) transcription factor is crucial in integrating these signals, and acts in part by activating the expression of multiple floral homeotic genes. Plants flower in response to both environmental and endogenous signals. ![]()
0 Comments
Leave a Reply. |
AuthorWrite something about yourself. No need to be fancy, just an overview. ArchivesCategories |