Photoperiodic responses, such as the daylength-dependent control of reproductive development, are associated with a circadian biological clock. The photoperiod-insensitive early-flowering 3 (elf3) mutant of Arabidopsis thaliana lacks rhythmicity in two distinct circadian-regulated processes. This defect was apparent only when plants were assayed under constant light conditions. elf3 mutants retain rhythmicity in constant dark and anticipate light/dark transitions under most light/dark regimes. The conditional arrhythmic phenotype suggests that the circadian pacemaker is intact in darkness in elf3 mutant plants, but the transduction of light signals to the circadian clock is impaired.
Flowering in Arabidopsis thaliana is promoted by longday (LD) photoperiods such that plants grown in LD flower earlier, and after the production of fewer leaves, than plants grown in short-day (SD) photoperiods. The early-flowering 3 (elf3) mutant of Arabidopsis, which is insensitive to photoperiod with regard to floral initiation has been characterized elf3 mutants are also altered in several aspects of vegetative photomorphogenesis, including hypocotyl elongation. When inhibition of hypocotyl elongation was measured, elf3 mutant seedlings were less responsive than wild-type to all wavelengths of light, and most notably defective in blue and green light-mediated inhibition. When analyzed for the flowering-time phenotype, elf3 was epistatic to mutant alleles of the blue-light receptor encoding gene, HY4. However, when elf3 mutants were made deficient for functional phytochrome by the introduction of hy2 mutant alleles, the elf3 hy2 double mutants displayed the novel phenotype of flowering earlier than either single mutant while still exhibiting photoperiod insensitivity, indicating that a phytochrome-mediated pathway regulating floral initiation remains functional in elf3 single mutants. In addition, the inflorescences of one allelic combination of elf3 hy2 double mutants form a terminal flower similar to the structure produced by tfk1 single mutants. These results suggest that one of the signal transduction pathways controlling photoperiodism in Arabidopsis is regulated, at least in part, by photoreceptors other than phytochrome, and that the activity of the Arabidopsis inflorescence and floral meristem identity genes may be regulated by this same pathway.
We present the initial phenotypic characterization of an Arabidopsis mutation, terminal flower 1-1 (tfll-1 ), that identifies a new genetic locus, TFL1. The tfll-1 mutation causes early flowering and limits the development of the normally indeterminate inflorescence by promoting the formation of a terminal floral meristem. lnflorescence development in mutant plants often terminates with a compound floral structure consisting of the terminal flower and one or two subtending lateral flowers. The distal-most flowers frequently contain chimeric floral organs. Light microscopic examination shows no structural aberrations in the vegetative meristem or in the inflorescence meristem before the formation of floral buttresses. The wild-type appearance of lateral flowers and observations of double mutant combinations of tfll-1 with the floral morphogenesis mutations apetala 7-1 (ap7-1), ap2-1, and agamous (as) suggest that the tfll-1 mutation does not affect normal floral meristems. Secondary flower formation usually associated with the apl-1 mutation is suppressed in the terminal flower, but not in the lateral flowers, of tfll-1 apl-1 double mutants. Our results suggest that tfll-1 perturbs the establishment and maintenance of the inflorescence meristem. The mutation lies on the top arm of chromosome 5 approximately 2.8 centimorgans from the restriction fragment length polymorphism marker 217.
We present the initial phenotypic characterization of an Arabidopsis mutation, terminal flower 1-1 (tfl1-1), that identifies a new genetic locus, TFL1. The tfl1-1 mutation causes early flowering and limits the development of the normally indeterminate inflorescence by promoting the formation of a terminal floral meristem. Inflorescence development in mutant plants often terminates with a compound floral structure consisting of the terminal flower and one or two subtending lateral flowers. The distal-most flowers frequently contain chimeric floral organs. Light microscopic examination shows no structural aberrations in the vegetative meristem or in the inflorescence meristem before the formation of floral buttresses. The wild-type appearance of lateral flowers and observations of double mutant combinations of tfl1-1 with the floral morphogenesis mutations apetala 1-1 (ap1-1), ap2-1, and agamous (ag) suggest that the tfl1-1 mutation does not affect normal floral meristems. Secondary flower formation usually associated with the ap1-1 mutation is suppressed in the terminal flower, but not in the lateral flowers, of tfl1-1 ap1-1 double mutants. Our results suggest that tfl1-1 perturbs the establishment and maintenance of the inflorescence meristem. The mutation lies on the top arm of chromosome 5 approximately 2.8 centimorgans from the restriction fragment length polymorphism marker 217.
Sequence analysis of five gene families that were isolated from tobacco thin cell layer explants initiating floral development [Meeks-Wagner et al. (1989). Plant Cell 1, [25][26][27][28][29][30][31][32][33][34][35] showed that two encode the pathogenesis-related proteins basic chitinase and basic ,B-l,3-glucanase, while a third encodes the cell wall protein extensin, which also accumulates during pathogen attack. Another sequence family encodes the water stress-induced protein osmotin [Singh et al. (1989). Plant Physiol. 90, 1096-11011. We found that osmotin was also induced by vira1 infection and wounding and, hence, could be considered a pathogenesis-related protein. These genes, which were highly expressed in explants during de novo flower formation but not in explants forming vegetative shoots [MeeksWagner et al. (1989). Plant Cell 1, 25-35], were also regulated developmentally in day-neutra1 and photoresponsive tobacco plants with high expression levels in the roots and moderate-to low-leve1 expression in other plant organs including flowers. An unidentified gene family, FB7-4, had its highest leve1 of expression in the basal internodes. Our findings indicate that these genes, some of which are conventionally considered to encode pathogen-related proteins, also have a complex association with normal developmental processes, including the floral response, in healthy plants.
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