Abstract
BackgroundIn wheat, the vernalization requirement is mainly controlled by the VRN genes. Different species of hexaploid and tetraploid wheat are widely used as genetic source for new mutant variants and alleles for fundamental investigations and practical breeding programs. In this study, VRN-A1 and VRN-B1 were analysed for 178 accessions representing six tetraploid wheat species (Triticum dicoccoides, T. dicoccum, T. turgidum, T. polonicum, T. carthlicum, T. durum) and five hexaploid species (T. compactum, T. sphaerococcum, T. spelta, T. macha, T. vavilovii).ResultsNovel allelic variants in the promoter region of VRN-A1 and VRN-B1 were identified based on the change in curvature and flexibility of the DNA molecules. The new variants of VRN-A1 (designated as Vrn-A1a.2, Vrn-A1b.2 – Vrn-A1b.6 and Vrn-A1i) were found to be widely distributed in hexaploid and tetraploid wheat, and in fact were predominant over the known VRN-A1 alleles. The greatest diversity of the new variants of VRN-B1 (designated as VRN-B1.f, VRN-B1.s and VRN-B1.m) was found in the tetraploid and some hexaploid wheat species.For the first time, minor differences within the sequence motif known as the VRN-box of VRN1 were correlated with wheat growth habit. Thus, vrn-A1b.3 and vrn-A1b.4 were revealed in winter wheat in contrast to Vrn-A1b.2, Vrn-A1b.5, Vrn-A1b.6 and Vrn-A1i. It was found that single nucleotide mutation in the VRN-box can influence the vernalization requirement and growth habit of wheat. Our data suggest that both the A-tract and C-rich segment within the VRN-box contribute to its functionality, and provide a new view of the hypothesised role of the VRN-box in regulating transcription of the VRN1 genes. Specifically, it is proposed that combination of mutations in this region can modulate vernalization sensitivity and flowering time of wheat.ConclusionsNew allelic variants of the VRN-A1 and VRN-B1 genes were identified in hexaploid and tetraploid wheat. Mutations in A-tract and C-rich segments within the VRN-box of VRN-A1 are associated with modulation of the vernalization requirement and flowering time. New allelic variants will be useful in fundamental investigations into the regulation of VRN1 expression, and provide a valuable genetic resource for practical breeding of wheat.Electronic supplementary materialThe online version of this article (doi:10.1186/s12870-015-0691-2) contains supplementary material, which is available to authorized users.
Highlights
In wheat, the vernalization requirement is mainly controlled by the VRN genes
The vernalization requirement and growth habit in wheat is largely controlled by four major loci, which are critical in determining flowering and maturity times: these include VRN1, VRN2, VRN3 and VRN4 (MADS-box transcription factor) [1,2,3,4]
VRN3 proteins are transported from the leaves to the shoot apical meristem [7] where they interact with transcription factor FDL2 (FLOWERING LOCUS D-like2) resulting in the formation of a protein complex that activates expression of the VRN1 genes [3, 8] and likely its paralogs FUL2 (FRUITFULL 2) and FUL3 [9]
Summary
The vernalization requirement is mainly controlled by the VRN genes. Different species of hexaploid and tetraploid wheat are widely used as genetic source for new mutant variants and alleles for fundamental investigations and practical breeding programs. The vernalization requirement determines the need for a prolonged exposure to low temperature in order for plants to transition to the reproductive phase of development According to their response to vernalization, wheat plants can be categorised as winter (strong vernalization sensitivity), spring (not sensitive to vernalization), or facultative types (intermediate growth habit). VRN3 proteins are transported from the leaves to the shoot apical meristem [7] where they interact with transcription factor FDL2 (FLOWERING LOCUS D-like2) resulting in the formation of a protein complex that activates expression of the VRN1 genes [3, 8] and likely its paralogs FUL2 (FRUITFULL 2) and FUL3 [9]. It is assumed that VRN4 is active in the leaves and operates upstream (or is a part) of the VRN1/VRN2/VRN3 feedback loop, VRN1 is the earliest target (direct or indirect) of VRN-D4 among these three genes [4]
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