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PubMed1997

Expression of heterologous phytochromes A, B or C in transgenic tobacco plants alters vegetative development and flowering time.

In this study, oat phytochrome A (phyA), Arabidopsis phytochrome B (phyB) or Arabidopsis phytochrome C (phyC) were expressed in both day-neutral and photo-period-sensitive (short-day) tobacco (Nicotiana tabacum cv. Hicks). Introgression of the Maryland Mammoth (MM) gene into cv Hicks was used to confer short-day photo-periodic sensitivity. Expression of oat phyA led to characteristic hypersensitivity of hypocotyls to red light (R) and far-red light (FR) and an overall dwarfing of the mature plant. Expression of Arabidopsis phyB enhanced the sensitivity of hypocotyls to R and caused even more marked dwarfing of the mature plant. In contrast, the expression of Arabidopsis phyC had no detectable consequences for the photocontrol of hypocotyl elongation. However, phyC expression did lead to a R-dependent increase in cotyledon expansion in de-etiolating seedlings and to a significant increase in leaf area in mature plants. This provides the first experimental evidence that phyC is biologically active. The flowering time of cv Hicks plants grown under 8 h photoperiods was virtually unaffected by a 30 min white light (W) night break given 8 h into the dark period. In contrast, cv Hicks MM plants responded to a night break with a delay in flowering. Expression of phyA or phyB led to a night break-dependent delay in flowering in cv Hicks plants. For cv Hicks MM plants, the expression of any of phyA, phyB or phyC caused a marked enhancement of the flower-delaying effect of a night break. These observations indicate that transgenic phyA, phyB or phyC can interact with the endogenous mechanisms controlling flowering time in tobacco.

Apoproteins↗

PubMed1999

The effect of seed and rosette cold treatment on germination and flowering time in some Arabidopsis thaliana (Brassicaceae) ecotypes.

The germination and flowering responses to cold treatment were investigated in 32 ecotypes of Arabidopsis thaliana. A month-long cold treatment at the seed stage decreased the time until flowering in all but one strain, whereas a 3-d cold treatment had little, or the opposing effect. A month-long cold treatment at the rosette stage also decreased the time until flowering, but was less effective than seed cold treatment. Seed and rosette cold treatments did not have an additive effect on time until flowering. Cold treatment usually increased the speed of germination, however no clear response patterns for the probability of germination were detected. These findings are discussed in relation to the life cycle of the plant.

Journal Article↗

PubMed2002

DNA polymorphism at the FRIGIDA gene in Arabidopsis thaliana: extensive nonsynonymous variation is consistent with local selection for flowering time.

FRIGIDA (FRI) is a major gene involved in the regulation of flowering time in Arabidopsis thaliana. Nucleotide variation at this gene was investigated by sequencing 25 field ecotypes collected from western Europe. Genetic diversity at FRI was characterized by a high number of haplotypes and an excess of low-frequency polymorphisms. A large excess of intraspecific nonsynonymous variation associated with low synonymous variation was detected along the first exon in the FRI gene. In contrast, no excess of nonsynonymous divergence was detected between A. thaliana and A. lyrata. The Tajima and McDonald and Kreitman tests, however, suggested that this gene has evolved in a nonneutral fashion. Nonsynonymous variation included eight loss-of-function mutations that have probably arisen recently and independently in several locations. A phenotypic evaluation of the sequenced ecotypes confirmed that these loss-of-function mutations were associated with an early-flowering phenotype. Taken together, our results suggest that DNA polymorphism at the FRI gene in A. thaliana from western Europe has been shaped by recent positive selection for earliness in a set of isolated populations.

Arabidopsis↗

PubMed1994

Mapping FRI, a locus controlling flowering time and vernalization response in Arabidopsis thaliana.

Two loci FRI (FRIGIDA) and KRY (KRYOPHILA) have previously been identified as having major influences on the flowering time of the late-flowering, vernalization-responsive Arabidopsis ecotype, Stockholm. We report here on the mapping and subsequent analysis of these two loci. FRI was mapped to the top of chromosome 4 between markers w122 and m506, using restriction fragment length polymorphism (RFLP) analysis. Due to lack of segregation in of the late-flowering phenotype under the environmental conditions used, KRY could only be localized, by "subtractive genotyping", to chromosome 5 or part of chromosome 3. The map position of FRI indicates that it is not allelic to any of the late-flowering loci identified by mutagenesis of the early-flowering ecotype Landsberg erecta. The late-flowering phenotype conferred by the Stockholm allele of FRI is modified (towards earlier flowering) by Landsberg erecta alleles at an unknown number of loci, perhaps accounting for the absence of fri mutations among mutant lines recovered in Landsberg erecta.

Alleles↗

PubMed2001

Functional importance of conserved domains in the flowering-time gene CONSTANS demonstrated by analysis of mutant alleles and transgenic plants.

CONSTANS promotes flowering of Arabidopsis in response to long-day conditions. We show that CONSTANS is a member of an Arabidopsis gene family that comprises 16 other members. The CO-Like proteins encoded by these genes contain two segments of homology: a zinc finger containing region near their amino terminus and a CCT (CO, CO-Like, TOC1) domain near their carboxy terminus. Analysis of seven classical co mutant alleles demonstrated that the mutations all occur within either the zinc finger region or the CCT domain, confirming that the two regions of homology are important for CO function. The zinc fingers are most similar to those of B-boxes, which act as protein-protein interaction domains in several transcription factors described in animals. Segments of CO protein containing the CCT domain localize GFP to the nucleus, but one mutation that affects the CCT domain delays flowering without affecting the nuclear localization function, suggesting that this domain has additional functions. All eight co alleles, including one recovered by pollen irradiation in which DNA encoding both B-boxes is deleted, are shown to be semidominant. This dominance appears to be largely due to a reduction in CO dosage in the heterozygous plants. However, some alleles may also actively delay flowering, because overexpression from the CaMV 35S promoter of the co-3 allele, that has a mutation in the second B-box, delayed flowering of wild-type plants. The significance of these observations for the role of CO in the control of flowering time is discussed.

Alleles↗

PubMed2001

Analysis of flowering time control in Arabidopsis by comparison of double and triple mutants.

Three genetic pathways promote flowering of Arabidopsis under long photoperiods. These pathways are represented by the genes CO, FCA, and GA1, which act in the long-day, autonomous, and gibberellin pathways, respectively. To test whether these are the only pathways that promote flowering under long photoperiods, the co-2 fca-1 ga1-3 triple mutant was constructed. These plants never flowered under long- or short-day conditions, indicating that the three pathways impaired by these mutations are absolutely required for flowering under these conditions. The triple mutant background represents a "vegetative ground state" enabling the roles of single pathways to be described in the corresponding double mutants. The phenotypes of plants carrying all eight combinations of wild-type and mutant alleles at the three loci were compared under long- and short-day conditions. This analysis demonstrated that under long photoperiods the long-day pathway promoted flowering most effectively, whereas under short photoperiods the gibberellin pathway had the strongest effect. The autonomous pathway had a weak effect when acting alone under either photoperiod but appeared to play an important role in facilitating the promotion of flowering by the other two pathways. The vegetative phenotype of the triple mutant could be overcome by vernalization, suggesting that a fourth pathway promoted flowering under these conditions. These observations are discussed in light of current models describing the regulation of flowering time in Arabidopsis.

Arabidopsis↗

PubMed1999

Late-flowering genes interact with early-flowering genes to regulate flowering time in Arabidopsis thaliana.

To investigate the genetic mechanisms regulating the transition from the vegetative to reproductive growth in Arabidopsis, double mutants between three different early-flowering mutants, early flowering 1-1, 2-1, 3-1, (elf 1-1, 2-1, 3-1) and five different late-flowering mutants, gi-1, ft-1, fwa-1, ld-1, and fca-9, were constructed and phenotypes analyzed. Double mutants in all combinations displayed the late-flowering phenotypes which resembled their respective late-flowering parents in both flowering time and the number of vegetative leaves produced. The results indicate that five late-flowering mutants are epistatic to all three early-flowering mutants tested here. This epistatic relationship suggests that ELF1, ELF2, and ELF3 genes function upstream of these five late-flowering genes no matter if they are functioning in autonomous or photoperiod pathways. These three early-flowering genes may negatively modify the activity of most late-flowering genes to influence the time of the vegetative-to-reproductive transition in Arabidopsis.

Arabidopsis↗

PubMed2003

The function of the flowering time gene AGL20 is conserved in Crucifers.

The MADS box gene, AGAMOUS-LIKE 20 (AGL20), integrates environmental and endogenous flowering signals in Arabidopsis thaliana. In order to determine if its role is conserved in other plants, we isolated AGL20 orthologs from Brassica campestris, Cardamine flexuosa and Draba nemorosa. The putative amino acid sequences of the orthologs were 94 to 97% identical. We analyzed the flowering phenotype and expression level of the AGL20 ortholog in C. flexuosa, a long day plant that does not respond to vernalization. CaAGL20 was more highly expressed in long days than short days and its expression did not change in response to vernalization, indicating that its expression is correlated with flowering time, as in Arabidopsis. When the Brassica AGL20 ortholog was constitutively expressed in sense and antisense orientations using the 35S cauliflower mosaic virus promoter, some of the sense transgenic plants flowered extremely early and some of the antisense plants exhibited delayed flowering. These results suggest that the role of AGL20 is conserved in Crucifers.

Amino Acid Sequence↗

PubMed1997

FCA, a gene controlling flowering time in Arabidopsis, encodes a protein containing RNA-binding domains.

A strong promoter of the transition to flowering in Arabidopsis is encoded by FCA. FCA has been cloned and shown to encode a protein containing two RNA-binding domains and a WW protein interaction domain. This suggests that FCA functions in the posttranscriptional regulation of transcripts involved in the flowering process. The FCA transcript is alternatively spliced with only one form encoding the entire FCA protein. Plants carrying the FCA gene fused to the strong constitutive 35S promoter flowered earlier, and the ratio and abundance of the different FCA transcripts were altered. Thus, FCA appears to be a component of a posttranscriptional cascade involved in the control of flowering time.

Amino Acid Sequence↗

PubMed1995

Genetic and environmental control of flowering time in Arabidopsis.

Plants detect fluctuations in environmental conditions and in response to these changes they promote or delay flowering. Some of the genes that are required to regulate flowering time in response to environmental changes were identified recently and cloned from Arabidopsis. The study of these genes is establishing connections between plant physiology and the expression of the homeotic genes that are required for floral development.

Arabidopsis↗

PubMed1998

Flowering time: from photoperiodism to florigen.

An Arabidopsis blue-light receptor, Cry2, has been found to play a critical role in the photoperiodic control of flowering time; and genes have been identified that may control the production of a transmissible flower-inducing signal, which may turn out to be the long-elusive putative flowering hormone 'florigen'.

Arabidopsis↗

PubMed2005

Microarray analysis reveals vegetative molecular phenotypes of Arabidopsis flowering-time mutants.

The transition to flowering occurs at the shoot apex; however, most of the characterized genes that affect the timing of floral induction are expressed throughout the plant. To further our understanding of these genes and the flowering process, the vegetative molecular phenotypes of 16 Arabidopsis mutants associated with the major flowering initiation pathways were assayed using a 13,000 clone microarray under two different conditions that affect flowering. All mutants showed at least one change in gene expression other than the mutant flowering gene. Metabolism- and defence-related pathways were the areas with the most frequent gene expression changes detected in the mutants. Several genes such as EARLI1 were differentially expressed in a number of flowering mutants from different flowering pathways. Analysis of the promoter regions of genes differentially expressed identified common promoter elements, indicating some form of common regulation.

Arabidopsis↗

PubMed2004

Inflorescence structure and control of flowering time and duration by light in buckwheat (Fagopyrum esculentum Moench).

Morphogenesis of the reproductive structure of buckwheat and the impact of light conditions on flowering time and duration have been investigated using the variety 'La Harpe'. Inflorescences were initiated acropetally, in leaf axils, by the shoot apical meristem until its arrest of functioning which was accompanied by the abortion of the last inflorescence produced. The buckwheat inflorescence is a compound raceme that produces laterally flowered cymose clusters, the number of which was affected by the position of the inflorescence along the main stem. Similarly, the number of flowers in a lateral cluster was dependent on the inflorescence's position on the stem. The development of each inflorescence was stopped as its meristem stopped functioning and, in a situation reminiscent of the shoot apical meristem, the latest initiated cyme aborted. The development of each cyme was also terminated with the abortion of a few young flowers. The variety 'La Harpe' is a facultative short-day plant: the number of nodes generated before the initiation of the first inflorescence and the number of days from sowing to macroscopic appearance of this inflorescence were reduced in 8 h days as compared with 16 h days. The number of inflorescences, and thus flowering duration, was also strongly reduced by short days. It was unaffected by light irradiance in 8 h days while, in 16 h days, it was prolonged when light intensity was increased, suggesting the interaction of two different mechanisms for its regulation. Buckwheat is a distylous species, but inflorescence structure and flowering behaviour were not affected by floral morph.

Biological Clocks↗

PubMed1999

Genetic interactions of the Arabidopsis flowering time gene FCA, with genes regulating floral initiation.

The genes controlling the timing of the transition from vegetative to reproductive growth are likely candidates for regulators of genes initiating floral development. We have investigated the interaction of one particular gene controlling flowering time, FCA, with the meristem identity-genes TERMINAL FLOWER 1 (TFL1), APETALA 1 (AP1) and LEAFY (LFY) and the floral repression gene EMBRYONIC FLOWER 1 (EMF1). Double mutant combinations were generated and the phenotypes characterized. The influence of strong and intermediate fca mutant alleles on the phenotype conferred by a 35S-LFY transgene was also analysed. The results support a model where FCA function promotes flowering in multiple pathways, one leading to activation of LFY and AP1, and another acting in parallel with LFY and AP1. Only the latter pathway is predicted to be non-functional in the intermediate fca-4 allele. The results are also consistent with AP1 and TFL1 negatively regulating FCA function. Combination of Columbia fca and emf1 mutant alleles confirmed that FCA is required for the early flowering of emf1. EMF1 and FCA are therefore likely to operate in different floral pathways.

Alleles↗

PubMed2004

Haplotype structure and phenotypic associations in the chromosomal regions surrounding two Arabidopsis thaliana flowering time loci.

The feasibility of using linkage disequilbrium (LD) to fine-map loci underlying natural variation in Arabidopsis thaliana was investigated by looking for associations between flowering time and marker polymorphism in the genomic regions containing two candidate genes, FRI and FLC, both of which are known to contribute to natural variation in flowering. A sample of 196 accessions was used, and polymorphism was assessed by sequencing a total of 17 roughly 500-bp fragments. Using a novel Bayesian algorithm based on haplotype similarity, we demonstrate that LD could have been used to fine-map the FRI gene to a roughly 30-kb region and to identify two common loss-of-function alleles. Interestingly, because of genetic heterogeneity, simple single-marker associations would not have been able to map FRI with nearly the same precision. No clear evidence for previously unknown alleles at either locus was found, but the effect of population structure in causing false positives was evident.

Arabidopsis↗

PubMed1997

Characterization of two rice MADS box genes that control flowering time.

Plants contain a variety of the MADS box genes that encode regulatory proteins and play important roles in both the formation of flower meristem and the determination of floral organ identity. We have characterized two flower-specific cDNAs from rice, designated OsMADS7 and OsMADS8. The cDNAs displayed the structure of a typical plant MADS box gene, which consists of the MADS domain, I region, K domain, and C-terminal region. These genes were classified as members of the AGL2 gene family based on sequence homology. The OsMADS7 and 8 proteins were most homologous to OM1 and FBP2, respectively. The OsMADS7 and 8 transcripts were detectable primarily in carpels and also weakly in anthers. During flower development, the OsMADS genes started to express at the young flower stage and the expression continued to the late stage of flower development. The OsMADS7 and 8 genes were mapped on the long arms of the chromosome 8 and 9, respectively. To study the functions of the genes, the cDNA clones were expressed ectopically using the CaMV 35S promoter in a heterologous tobacco plant system. Transgenic plants expressing the OsMADS genes exhibited the phenotype of early flowering and dwarfism. The strength of the phenotypes was proportional to the levels of transgene expression and the phenotypes were co-inherited with the kanamycin resistant gene to the next generation. These results indicate that OsMADS7 and 8 are structurally related to the AGL2 family and are involved in controlling flowering time.

Amino Acid Sequence↗

PubMed2003

Ectopic expression of an orchid (Oncidium Gower Ramsey) AGL6-like gene promotes flowering by activating flowering time genes in Arabidopsis thaliana.

An AP1/AGL9 group of MADS box gene, OMADS1, with extensive homology to the Arabidopsis AGAMOUS-like 6 gene (AGL6) was characterized from orchid (Oncidium Gower Ramsey). OMADS1 mRNA was detected in apical meristem and in the lip and carpel of flower. Yeast two-hybrid analysis indicated that OMADS1 is able to strongly interact with OMADS3, a TM6-like protein that was involved in flower formation and floral initiation in orchid. Transgenic Arabidopsis and tobacco ectopically expressed OMADS1 showed similar novel phenotypes by significantly reducing plant size, flowering extremely early, and losing inflorescence indeterminacy. In addition, homeotic conversion of sepals into carpel-like structures and petals into staminoid structures were also observed in flowers of 35S::OMADS1 Arabidopsis. This result indicated that OMADS1 was involved in floral formation and initiation in transgenic plants. Further analysis indicated that the expression of flowering time genes FT, SUPPRESSOR OF OVEREXPRESSION OF CO 1 (SOC1) and flower meristem identity genes LEAFY (LFY), APETALA1 (AP1) was significantly up-regulated in 35S::OMADS1 transgenic Arabidopsis plants. Furthermore, ectopic expression of OMADS1 rescued late-flowering phenotype in gi-1, co-3 but not for ft-1 and fwa-1 mutants. These results supported that ectopic expression of OMADS1 influenced flower transition and formation by acting as an activator for FT and SOC1 in Arabidopsis.

Amino Acid Sequence↗

PubMed2004

Manipulation of the blue light photoreceptor cryptochrome 2 in tomato affects vegetative development, flowering time, and fruit antioxidant content.

Cryptochromes are blue light photoreceptors found in plants, bacteria, and animals. In Arabidopsis, cryptochrome 2 (cry2) is involved primarily in the control of flowering time and in photomorphogenesis under low-fluence light. No data on the function of cry2 are available in plants, apart from Arabidopsis (Arabidopsis thaliana). Expression of the tomato (Solanum lycopersicum) CRY2 gene was altered through a combination of transgenic overexpression and virus-induced gene silencing. Tomato CRY2 overexpressors show phenotypes similar to but distinct from their Arabidopsis counterparts (hypocotyl and internode shortening under both low- and high-fluence blue light), but also several novel ones, including a high-pigment phenotype, resulting in overproduction of anthocyanins and chlorophyll in leaves and of flavonoids and lycopene in fruits. The accumulation of lycopene in fruits is accompanied by the decreased expression of lycopene beta-cyclase genes. CRY2 overexpression causes an unexpected delay in flowering, observed under both short- and long-day conditions, and an increased outgrowth of axillary branches. Virus-induced gene silencing of CRY2 results in a reversion of leaf anthocyanin accumulation, of internode shortening, and of late flowering in CRY2-overexpressing plants, whereas in wild-type plants it causes a minor internode elongation.

Antioxidants↗