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The effect of day-neutral mutations in barley and wheat on the interaction between photoperiod and vernalization.

Turner AS, Faure S, Zhang Y, Laurie DA - Theor. Appl. Genet. (2013)

Bottom Line: When eam8 was crossed into a genetic background with a vernalization requirement Vrn-2 was expressed under all photoperiods and the early flowering phenotype was partially repressed in unvernalized (UV) plants, likely due to competition between the constitutively active photoperiod pathway and the repressing effect of Vrn-2.Short days were effective in promoting flowering in individuals wild type at Ppd-D1, but not in individuals that carry the Ppd-D1a mutation.As Ppd-D1a does not affect the circadian clock, this also shows that clock regulation of Vrn-2 operates indirectly through one or more downstream genes, one of which may be Ppd-1.

View Article: PubMed Central - PubMed

Affiliation: Department of Crop Genetics, John Innes Centre, Colney Lane, Norwich, UK. adrian.turner-crls@jic.ac.uk

ABSTRACT
Vernalization-2 (Vrn-2) is the major flowering repressor in temperate cereals. It is only expressed under long days in wild-type plants. We used two day-neutral (photoperiod insensitive) mutations that allow rapid flowering in short or long days to investigate the day length control of Vrn-2. The barley (Hordeum vulgare) early maturity8 (eam8) mutation affects the barley ELF3 gene. eam8 mutants disrupt the circadian clock resulting in elevated expression of Ppd-H1 and the floral activator HvFT1 under short or long days. When eam8 was crossed into a genetic background with a vernalization requirement Vrn-2 was expressed under all photoperiods and the early flowering phenotype was partially repressed in unvernalized (UV) plants, likely due to competition between the constitutively active photoperiod pathway and the repressing effect of Vrn-2. We also investigated the wheat (Triticum aestivum) Ppd-D1a mutation. This differs from eam8 in causing elevated levels of Ppd-1 and TaFT1 expression without affecting the circadian clock. We used genotypes that differed in "short-day vernalization". Short days were effective in promoting flowering in individuals wild type at Ppd-D1, but not in individuals that carry the Ppd-D1a mutation. The latter showed Vrn-2 expression in short days. In summary, eam8 and Ppd-D1a mimic long days in terms of photoperiod response, causing Vrn-2 to become aberrantly expressed (in short days). As Ppd-D1a does not affect the circadian clock, this also shows that clock regulation of Vrn-2 operates indirectly through one or more downstream genes, one of which may be Ppd-1.

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Vrn-2 (solid line) and HvCCA1 (dotted line) expression time courses in unvernalized ‘Igri’ plants entrained under 12 h light/12 h dark cycles then subjected to constant light. Error bars indicate standard error of the mean
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Fig3: Vrn-2 (solid line) and HvCCA1 (dotted line) expression time courses in unvernalized ‘Igri’ plants entrained under 12 h light/12 h dark cycles then subjected to constant light. Error bars indicate standard error of the mean

Mentions: Vrn-2 is a member of the CCT domain family of genes. Other members of this family are known to be components of, or regulated by, the circadian clock (Mizuno and Nakamichi 2005). Vrn-2 has previously been shown to have a diurnal change in expression when measured together with a closely related CCT gene (HvZCCTa and HvZCCTb in Trevaskis et al. 2006). These data suggested that Vrn-2 might have circadian control in wild-type plants. To test this we entrained UV ‘Igri’ plants in 12 h light/12 h dark conditions for 16 days and then moved them to continuous light and measured expression at 3 h intervals over 48 h. Vrn-2 expression was very low in the 12 h/12 h conditions, but rose rapidly 16 h after transfer to continuous light. Expression then fell during the subjective night and rose again at 56 h (Fig. 3). This showed circadian control of Vrn-2 in wild-type plants and also showed that expression was strongly induced by the first exposure to 16 h or more of light. The plants sampled for expression in Fig. 2 were harvested at the start of the day which explains the relatively low level of Vrn-2 expression in wild-type plants.Fig. 3


The effect of day-neutral mutations in barley and wheat on the interaction between photoperiod and vernalization.

Turner AS, Faure S, Zhang Y, Laurie DA - Theor. Appl. Genet. (2013)

Vrn-2 (solid line) and HvCCA1 (dotted line) expression time courses in unvernalized ‘Igri’ plants entrained under 12 h light/12 h dark cycles then subjected to constant light. Error bars indicate standard error of the mean
© Copyright Policy - OpenAccess
Related In: Results  -  Collection

Show All Figures
getmorefigures.php?uid=PMC3755224&req=5

Fig3: Vrn-2 (solid line) and HvCCA1 (dotted line) expression time courses in unvernalized ‘Igri’ plants entrained under 12 h light/12 h dark cycles then subjected to constant light. Error bars indicate standard error of the mean
Mentions: Vrn-2 is a member of the CCT domain family of genes. Other members of this family are known to be components of, or regulated by, the circadian clock (Mizuno and Nakamichi 2005). Vrn-2 has previously been shown to have a diurnal change in expression when measured together with a closely related CCT gene (HvZCCTa and HvZCCTb in Trevaskis et al. 2006). These data suggested that Vrn-2 might have circadian control in wild-type plants. To test this we entrained UV ‘Igri’ plants in 12 h light/12 h dark conditions for 16 days and then moved them to continuous light and measured expression at 3 h intervals over 48 h. Vrn-2 expression was very low in the 12 h/12 h conditions, but rose rapidly 16 h after transfer to continuous light. Expression then fell during the subjective night and rose again at 56 h (Fig. 3). This showed circadian control of Vrn-2 in wild-type plants and also showed that expression was strongly induced by the first exposure to 16 h or more of light. The plants sampled for expression in Fig. 2 were harvested at the start of the day which explains the relatively low level of Vrn-2 expression in wild-type plants.Fig. 3

Bottom Line: When eam8 was crossed into a genetic background with a vernalization requirement Vrn-2 was expressed under all photoperiods and the early flowering phenotype was partially repressed in unvernalized (UV) plants, likely due to competition between the constitutively active photoperiod pathway and the repressing effect of Vrn-2.Short days were effective in promoting flowering in individuals wild type at Ppd-D1, but not in individuals that carry the Ppd-D1a mutation.As Ppd-D1a does not affect the circadian clock, this also shows that clock regulation of Vrn-2 operates indirectly through one or more downstream genes, one of which may be Ppd-1.

View Article: PubMed Central - PubMed

Affiliation: Department of Crop Genetics, John Innes Centre, Colney Lane, Norwich, UK. adrian.turner-crls@jic.ac.uk

ABSTRACT
Vernalization-2 (Vrn-2) is the major flowering repressor in temperate cereals. It is only expressed under long days in wild-type plants. We used two day-neutral (photoperiod insensitive) mutations that allow rapid flowering in short or long days to investigate the day length control of Vrn-2. The barley (Hordeum vulgare) early maturity8 (eam8) mutation affects the barley ELF3 gene. eam8 mutants disrupt the circadian clock resulting in elevated expression of Ppd-H1 and the floral activator HvFT1 under short or long days. When eam8 was crossed into a genetic background with a vernalization requirement Vrn-2 was expressed under all photoperiods and the early flowering phenotype was partially repressed in unvernalized (UV) plants, likely due to competition between the constitutively active photoperiod pathway and the repressing effect of Vrn-2. We also investigated the wheat (Triticum aestivum) Ppd-D1a mutation. This differs from eam8 in causing elevated levels of Ppd-1 and TaFT1 expression without affecting the circadian clock. We used genotypes that differed in "short-day vernalization". Short days were effective in promoting flowering in individuals wild type at Ppd-D1, but not in individuals that carry the Ppd-D1a mutation. The latter showed Vrn-2 expression in short days. In summary, eam8 and Ppd-D1a mimic long days in terms of photoperiod response, causing Vrn-2 to become aberrantly expressed (in short days). As Ppd-D1a does not affect the circadian clock, this also shows that clock regulation of Vrn-2 operates indirectly through one or more downstream genes, one of which may be Ppd-1.

Show MeSH