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A genetic network of flowering-time genes in wheat leaves, in which an APETALA1/FRUITFULL-like gene, VRN1, is upstream of FLOWERING LOCUS T.

Shimada S, Ogawa T, Kitagawa S, Suzuki T, Ikari C, Shitsukawa N, Abe T, Kawahigashi H, Kikuchi R, Handa H, Murai K - Plant J. (2009)

Bottom Line: These results suggest that VRN1 is upstream of FT and upregulates the FT expression under LD conditions.These results suggest that in the transgenic plant, FT suppresses VRN2 expression, leading to an increase in VRN1 expression.Based on these results, we present a model for a genetic network of flowering-time genes in wheat leaves, in which VRN1 is upstream of FT with a positive feedback loop through VRN2.

View Article: PubMed Central - PubMed

Affiliation: Department of Bioscience, Fukui Prefectural University, Eiheiji-cho, Fukui, Japan.

ABSTRACT
To elucidate the genetic mechanism of flowering in wheat, we performed expression, mutant and transgenic studies of flowering-time genes. A diurnal expression analysis revealed that a flowering activator VRN1, an APETALA1/FRUITFULL homolog in wheat, was expressed in a rhythmic manner in leaves under both long-day (LD) and short-day (SD) conditions. Under LD conditions, the upregulation of VRN1 during the light period was followed by the accumulation of FLOWERING LOCUS T (FT) transcripts. Furthermore, FT was not expressed in a maintained vegetative phase (mvp) mutant of einkorn wheat (Triticum monococcum), which has alleles of VRN1, and never transits from the vegetative to the reproductive phase. These results suggest that VRN1 is upstream of FT and upregulates the FT expression under LD conditions. The overexpression of FT in a transgenic bread wheat (Triticum aestivum) caused extremely early heading with the upregulation of VRN1 and the downregulation of VRN2, a putative repressor gene of VRN1. These results suggest that in the transgenic plant, FT suppresses VRN2 expression, leading to an increase in VRN1 expression. Based on these results, we present a model for a genetic network of flowering-time genes in wheat leaves, in which VRN1 is upstream of FT with a positive feedback loop through VRN2. The mvp mutant has a allele of VRN2, as well as of VRN1, because it was obtained from a spring einkorn wheat strain lacking VRN2. The fact that FT is not expressed in the mvp mutant supports the present model.

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Analysis of phenotype and gene expression in transgenic wheat transformed with a 35S:VRN3-D construct. (a) A spikelet emerged from a transgenic T0 plant grown in a petri dish at the three-leaf stage under short-day (SD; 8-h light/16-h dark) conditions at 25°C. Scale bar: 2 cm. (b) Transgenic T1 plants derived from a T0 plant showing segregation for the presence (+) or absence (−) of the transgene. The T1-positive plant (left) showed early heading. The T1 (+) and (−) plants illustrated here correspond to plants 1 and 3 in (c), respectively. The plants were grown under SDs (10-h light/14-h dark) at 20°C, and were photographed at 64 days after sowing. Scale bar: 5 cm. (c) The expression of FT, VRN1 and VRN2 in T1 plants segregating for the FT transgene, and in non-transformants (i.e. wild type, WT). RT-PCR analysis was performed using the seedlings at the one-leaf stage. Gene expression levels were compared at the exponential phase of RT-PCR amplification. The Actin gene was used as an internal control. Numbers indicate the days to heading in each T1 plant. The plants were grown under SDs (10-h light/14-h dark) at 20°C. (d) Expression levels of FT, VRN1 and VRN2 in transformants 1 (positive) and 3 (negative), and non-transformant (WT) determined by real-time PCR analysis. The mRNA levels were normalized against the mRNA level of Actin.
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fig06: Analysis of phenotype and gene expression in transgenic wheat transformed with a 35S:VRN3-D construct. (a) A spikelet emerged from a transgenic T0 plant grown in a petri dish at the three-leaf stage under short-day (SD; 8-h light/16-h dark) conditions at 25°C. Scale bar: 2 cm. (b) Transgenic T1 plants derived from a T0 plant showing segregation for the presence (+) or absence (−) of the transgene. The T1-positive plant (left) showed early heading. The T1 (+) and (−) plants illustrated here correspond to plants 1 and 3 in (c), respectively. The plants were grown under SDs (10-h light/14-h dark) at 20°C, and were photographed at 64 days after sowing. Scale bar: 5 cm. (c) The expression of FT, VRN1 and VRN2 in T1 plants segregating for the FT transgene, and in non-transformants (i.e. wild type, WT). RT-PCR analysis was performed using the seedlings at the one-leaf stage. Gene expression levels were compared at the exponential phase of RT-PCR amplification. The Actin gene was used as an internal control. Numbers indicate the days to heading in each T1 plant. The plants were grown under SDs (10-h light/14-h dark) at 20°C. (d) Expression levels of FT, VRN1 and VRN2 in transformants 1 (positive) and 3 (negative), and non-transformant (WT) determined by real-time PCR analysis. The mRNA levels were normalized against the mRNA level of Actin.

Mentions: Using spring wheat cv. Norin 61 (N61), we developed transgenic plants with VRN3-D cDNA driven by P35S. VRN3-D is a homoeolog of wheat FT (VRN3) located on the D genome. In culture in a petri dish, a transgenic T0 plant with overexpression of FT showed extremely early heading (Figure 6a), indicating that FT is a strong activator of the flowering pathway. Transgenic wheat plants were grown in a growth chamber under SDs. mRNAs were extracted from leaves of non-vernalized seedlings at the one-leaf stage, and the expression levels of FT, VRN1 and VRN2 were examined. At this stage, the SAMs of transgenic and non-transgenic (WT) wheat are still in the vegetative phase. In WT plants, the expression of FT and VRN1 were not observed, whereas a high expression of VRN2 was detected (Figure 6c). Overexpression of FT was observed in 10 T1 plants, 1, 2, 4, 5, 9, 11 and 13–16, which showed an early heading trait compared with non-transgenic plants (Figure 6b, c). To investigate whether the RT-PCR patterns of FT showed expression profiles of the VRN3-D transgene, the amplified RT-PCR products of positive transgenic lines 4 and 5 were cloned and sequenced. The sequences of RT-PCR products were identical with those of VRN3-D, and differed from the sequences of VRN3-A and VRN3-B (Figure S5), indicating that the RT-PCR analysis of FT exhibited the expression profile of the VRN3-D transgene.


A genetic network of flowering-time genes in wheat leaves, in which an APETALA1/FRUITFULL-like gene, VRN1, is upstream of FLOWERING LOCUS T.

Shimada S, Ogawa T, Kitagawa S, Suzuki T, Ikari C, Shitsukawa N, Abe T, Kawahigashi H, Kikuchi R, Handa H, Murai K - Plant J. (2009)

Analysis of phenotype and gene expression in transgenic wheat transformed with a 35S:VRN3-D construct. (a) A spikelet emerged from a transgenic T0 plant grown in a petri dish at the three-leaf stage under short-day (SD; 8-h light/16-h dark) conditions at 25°C. Scale bar: 2 cm. (b) Transgenic T1 plants derived from a T0 plant showing segregation for the presence (+) or absence (−) of the transgene. The T1-positive plant (left) showed early heading. The T1 (+) and (−) plants illustrated here correspond to plants 1 and 3 in (c), respectively. The plants were grown under SDs (10-h light/14-h dark) at 20°C, and were photographed at 64 days after sowing. Scale bar: 5 cm. (c) The expression of FT, VRN1 and VRN2 in T1 plants segregating for the FT transgene, and in non-transformants (i.e. wild type, WT). RT-PCR analysis was performed using the seedlings at the one-leaf stage. Gene expression levels were compared at the exponential phase of RT-PCR amplification. The Actin gene was used as an internal control. Numbers indicate the days to heading in each T1 plant. The plants were grown under SDs (10-h light/14-h dark) at 20°C. (d) Expression levels of FT, VRN1 and VRN2 in transformants 1 (positive) and 3 (negative), and non-transformant (WT) determined by real-time PCR analysis. The mRNA levels were normalized against the mRNA level of Actin.
© Copyright Policy - open-access
Related In: Results  -  Collection

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fig06: Analysis of phenotype and gene expression in transgenic wheat transformed with a 35S:VRN3-D construct. (a) A spikelet emerged from a transgenic T0 plant grown in a petri dish at the three-leaf stage under short-day (SD; 8-h light/16-h dark) conditions at 25°C. Scale bar: 2 cm. (b) Transgenic T1 plants derived from a T0 plant showing segregation for the presence (+) or absence (−) of the transgene. The T1-positive plant (left) showed early heading. The T1 (+) and (−) plants illustrated here correspond to plants 1 and 3 in (c), respectively. The plants were grown under SDs (10-h light/14-h dark) at 20°C, and were photographed at 64 days after sowing. Scale bar: 5 cm. (c) The expression of FT, VRN1 and VRN2 in T1 plants segregating for the FT transgene, and in non-transformants (i.e. wild type, WT). RT-PCR analysis was performed using the seedlings at the one-leaf stage. Gene expression levels were compared at the exponential phase of RT-PCR amplification. The Actin gene was used as an internal control. Numbers indicate the days to heading in each T1 plant. The plants were grown under SDs (10-h light/14-h dark) at 20°C. (d) Expression levels of FT, VRN1 and VRN2 in transformants 1 (positive) and 3 (negative), and non-transformant (WT) determined by real-time PCR analysis. The mRNA levels were normalized against the mRNA level of Actin.
Mentions: Using spring wheat cv. Norin 61 (N61), we developed transgenic plants with VRN3-D cDNA driven by P35S. VRN3-D is a homoeolog of wheat FT (VRN3) located on the D genome. In culture in a petri dish, a transgenic T0 plant with overexpression of FT showed extremely early heading (Figure 6a), indicating that FT is a strong activator of the flowering pathway. Transgenic wheat plants were grown in a growth chamber under SDs. mRNAs were extracted from leaves of non-vernalized seedlings at the one-leaf stage, and the expression levels of FT, VRN1 and VRN2 were examined. At this stage, the SAMs of transgenic and non-transgenic (WT) wheat are still in the vegetative phase. In WT plants, the expression of FT and VRN1 were not observed, whereas a high expression of VRN2 was detected (Figure 6c). Overexpression of FT was observed in 10 T1 plants, 1, 2, 4, 5, 9, 11 and 13–16, which showed an early heading trait compared with non-transgenic plants (Figure 6b, c). To investigate whether the RT-PCR patterns of FT showed expression profiles of the VRN3-D transgene, the amplified RT-PCR products of positive transgenic lines 4 and 5 were cloned and sequenced. The sequences of RT-PCR products were identical with those of VRN3-D, and differed from the sequences of VRN3-A and VRN3-B (Figure S5), indicating that the RT-PCR analysis of FT exhibited the expression profile of the VRN3-D transgene.

Bottom Line: These results suggest that VRN1 is upstream of FT and upregulates the FT expression under LD conditions.These results suggest that in the transgenic plant, FT suppresses VRN2 expression, leading to an increase in VRN1 expression.Based on these results, we present a model for a genetic network of flowering-time genes in wheat leaves, in which VRN1 is upstream of FT with a positive feedback loop through VRN2.

View Article: PubMed Central - PubMed

Affiliation: Department of Bioscience, Fukui Prefectural University, Eiheiji-cho, Fukui, Japan.

ABSTRACT
To elucidate the genetic mechanism of flowering in wheat, we performed expression, mutant and transgenic studies of flowering-time genes. A diurnal expression analysis revealed that a flowering activator VRN1, an APETALA1/FRUITFULL homolog in wheat, was expressed in a rhythmic manner in leaves under both long-day (LD) and short-day (SD) conditions. Under LD conditions, the upregulation of VRN1 during the light period was followed by the accumulation of FLOWERING LOCUS T (FT) transcripts. Furthermore, FT was not expressed in a maintained vegetative phase (mvp) mutant of einkorn wheat (Triticum monococcum), which has alleles of VRN1, and never transits from the vegetative to the reproductive phase. These results suggest that VRN1 is upstream of FT and upregulates the FT expression under LD conditions. The overexpression of FT in a transgenic bread wheat (Triticum aestivum) caused extremely early heading with the upregulation of VRN1 and the downregulation of VRN2, a putative repressor gene of VRN1. These results suggest that in the transgenic plant, FT suppresses VRN2 expression, leading to an increase in VRN1 expression. Based on these results, we present a model for a genetic network of flowering-time genes in wheat leaves, in which VRN1 is upstream of FT with a positive feedback loop through VRN2. The mvp mutant has a allele of VRN2, as well as of VRN1, because it was obtained from a spring einkorn wheat strain lacking VRN2. The fact that FT is not expressed in the mvp mutant supports the present model.

Show MeSH
Related in: MedlinePlus