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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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Diurnal expression patterns of GI, CO, FT and VRN1 in spring wheat cv. Triple Dirk plants with Ppd dominant alleles (Ppd-TD), grown under long-day (LD) or short-day (SD) conditions. The expression patterns of GI (a and b), CO (WCO1 and TaHd1) (c and d), FT (e and f) and VRN1 (g and h) were analyzed by real-time PCR using TD plants at the three-leaf stage grown under LDs (16-h light/8-h dark) (a, c, e, g) or SDs (10-h light/14-h dark) (b, d, f, h) at 20°C. The Ubiquitin (Ubi-1) gene was used as an internal control for calculating the relative levels of GI, CO (WCO1 and TaHd1), FT and VRN1 genes. Each point represents the average of two replicates, and the error bars indicate the range. The white and black bars along the horizontal axes represent light and dark periods, respectively. The numbers on the horizontal axes indcate the time in hours.
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fig02: Diurnal expression patterns of GI, CO, FT and VRN1 in spring wheat cv. Triple Dirk plants with Ppd dominant alleles (Ppd-TD), grown under long-day (LD) or short-day (SD) conditions. The expression patterns of GI (a and b), CO (WCO1 and TaHd1) (c and d), FT (e and f) and VRN1 (g and h) were analyzed by real-time PCR using TD plants at the three-leaf stage grown under LDs (16-h light/8-h dark) (a, c, e, g) or SDs (10-h light/14-h dark) (b, d, f, h) at 20°C. The Ubiquitin (Ubi-1) gene was used as an internal control for calculating the relative levels of GI, CO (WCO1 and TaHd1), FT and VRN1 genes. Each point represents the average of two replicates, and the error bars indicate the range. The white and black bars along the horizontal axes represent light and dark periods, respectively. The numbers on the horizontal axes indcate the time in hours.

Mentions: The diurnal expression patterns of GI (TaGI1), CO (WCO1 and TaHd1) and FT (VRN3) were examined in leaves at the three-leaf stage in spring wheat cv. Triple Dirk (TD) plants with Ppd dominant alleles (Ppd-TD), grown under LD or SD conditions (Figure 2). The expression analysis was performed using real-time PCR with primers that amplify all three homoeologs located on A, B and D wheat genomes. The shoot apical meristem (SAM) of the Ppd-TD plant transits from the vegetative to reproductive phase around at the four-leaf stage when grown under LD conditions. Under SD conditions the timing of the phase transition is a little delayed (occurring at the five-leaf stage). Under LD conditions, GI mRNA accumulated during the light period, and expression peaked late in the light phase (Figure 2a). CO (WCO1 and TaHd1) mRNA accumulated during the dark period (Figure 2c), and FT mRNA accumulated from the beginning of the light phase (Figure 2e). Under SD conditions, GI mRNA expression showed a similar pattern as under LD conditions, although the peak of expression was shifted towards the end of the light period (Figure 2b). CO (WCO1 and TaHd1) expression also showed a similar pattern as under LD conditions, but the WCO1 expression was mostly confined to the dark period under SDs (Figure 2d). In contrast to GI and CO, no expression of FT was detected under SD conditions (Figure 2f). The expression analysis did not conflict with the idea that the functional hierarchy, GI → CO → FT, is conserved in wheat. Analysis of the diurnal expression pattern in barley also indicated conservation of this cascade (Turner et al., 2005).


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)

Diurnal expression patterns of GI, CO, FT and VRN1 in spring wheat cv. Triple Dirk plants with Ppd dominant alleles (Ppd-TD), grown under long-day (LD) or short-day (SD) conditions. The expression patterns of GI (a and b), CO (WCO1 and TaHd1) (c and d), FT (e and f) and VRN1 (g and h) were analyzed by real-time PCR using TD plants at the three-leaf stage grown under LDs (16-h light/8-h dark) (a, c, e, g) or SDs (10-h light/14-h dark) (b, d, f, h) at 20°C. The Ubiquitin (Ubi-1) gene was used as an internal control for calculating the relative levels of GI, CO (WCO1 and TaHd1), FT and VRN1 genes. Each point represents the average of two replicates, and the error bars indicate the range. The white and black bars along the horizontal axes represent light and dark periods, respectively. The numbers on the horizontal axes indcate the time in hours.
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC2721963&req=5

fig02: Diurnal expression patterns of GI, CO, FT and VRN1 in spring wheat cv. Triple Dirk plants with Ppd dominant alleles (Ppd-TD), grown under long-day (LD) or short-day (SD) conditions. The expression patterns of GI (a and b), CO (WCO1 and TaHd1) (c and d), FT (e and f) and VRN1 (g and h) were analyzed by real-time PCR using TD plants at the three-leaf stage grown under LDs (16-h light/8-h dark) (a, c, e, g) or SDs (10-h light/14-h dark) (b, d, f, h) at 20°C. The Ubiquitin (Ubi-1) gene was used as an internal control for calculating the relative levels of GI, CO (WCO1 and TaHd1), FT and VRN1 genes. Each point represents the average of two replicates, and the error bars indicate the range. The white and black bars along the horizontal axes represent light and dark periods, respectively. The numbers on the horizontal axes indcate the time in hours.
Mentions: The diurnal expression patterns of GI (TaGI1), CO (WCO1 and TaHd1) and FT (VRN3) were examined in leaves at the three-leaf stage in spring wheat cv. Triple Dirk (TD) plants with Ppd dominant alleles (Ppd-TD), grown under LD or SD conditions (Figure 2). The expression analysis was performed using real-time PCR with primers that amplify all three homoeologs located on A, B and D wheat genomes. The shoot apical meristem (SAM) of the Ppd-TD plant transits from the vegetative to reproductive phase around at the four-leaf stage when grown under LD conditions. Under SD conditions the timing of the phase transition is a little delayed (occurring at the five-leaf stage). Under LD conditions, GI mRNA accumulated during the light period, and expression peaked late in the light phase (Figure 2a). CO (WCO1 and TaHd1) mRNA accumulated during the dark period (Figure 2c), and FT mRNA accumulated from the beginning of the light phase (Figure 2e). Under SD conditions, GI mRNA expression showed a similar pattern as under LD conditions, although the peak of expression was shifted towards the end of the light period (Figure 2b). CO (WCO1 and TaHd1) expression also showed a similar pattern as under LD conditions, but the WCO1 expression was mostly confined to the dark period under SDs (Figure 2d). In contrast to GI and CO, no expression of FT was detected under SD conditions (Figure 2f). The expression analysis did not conflict with the idea that the functional hierarchy, GI → CO → FT, is conserved in wheat. Analysis of the diurnal expression pattern in barley also indicated conservation of this cascade (Turner et al., 2005).

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