HvFT1 polymorphism and effect – survey of barley germplasm and expression analysis

Loscos J, Igartua E, Contreras-Moreira B, Gracia MP and Casas AM (2014) HvFT1 polymorphism and effect – survey of barley germplasm and expression analysis. Front. Plant Sci., doi: 10.3389/fpls.2014.00251

Flowering time in plants is a tightly regulated process. In barley (Hordeum vulgare L.),
HvFT1, ortholog of FLOWERING LOCUS T, is the main integrator of the photoperiod and
vernalization signals leading to the transition from vegetative to reproductive state of the
plant. This gene presents sequence polymorphisms affecting flowering time in the first
intron and in the promoter. Recently, copy number variation (CNV) has been described
for this gene. An allele with more than one copy was linked to higher gene expression,
earlier flowering, and an overriding effect of the vernalization mechanism. This study aims
at (1) surveying the distribution of HvFT1 polymorphisms across barley germplasm and (2)
assessing gene expression and phenotypic effects of HvFT1 alleles. We analyzed HvFT1
CNV in 109 winter, spring, and facultative barley lines. There was more than one copy
of the gene (2–5) only in spring or facultative barleys without a functional vernalization
VrnH2 allele. CNV was investigated in several regions inside and around HvFT1. Two
models of the gene were found: one with the same number of promoters and transcribed
regions, and another with one promoter and variable number of transcribed regions. This
last model was found in Nordic barleys only. Analysis of HvFT1 expression showed that
association between known polymorphisms at the HvFT1 locus and the expression of
the gene was highly dependent on the genetic background. Under long day conditions
the earliest flowering lines carried a sensitive PpdH1 allele. Among spring cultivars with
different number of copies, no clear relation was found between CNV, gene expression
and flowering time. This was confirmed in a set of doubled haploid lines of a population
segregating for HvFT1 CNV. Earlier flowering in the presence of several copies of HvFT1
was only seen in cultivar Tammi, which carries one promoter, suggesting a relation of gene
structure with its regulation. HvCEN also affected to a large extent flowering time.