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.

Vernalization requirement in hexaploid wheat is largely controlled by a series of homoeologous VERNALIZATION (Vrn) genes, Vrn-A1, Vrn-B1, and Vrn-D1. The sequence of the promoter area and first intron of Vrn-D1 were analysed in 77 hexaploid accessions, representing five wheat species (Triticum compactum, Triticum sphaerococcum, Triticum spelta, Triticum vavilovii, and Triticum macha) sampled from different ecogeographic areas within 35 countries. Polymorphism was detected in the Vrn-D1 promoter, resulting in a new Vrn-D1 haplotype (named here, Hap-8T). Analysis of Vrn-D1 intron-1 sequences revealed a novel insertional mutation in a subset of T. spelta and T. compactum accessions. This mutant allele was designated Vrn-D1s. Analysis of the 844 bp insertion revealed it to be a nov el tra nspo sab le DNA e l emen t (nam ed DTA_Chimera_KF800714) not previously described in Triticum, belonging to the hAT superfamily. Finally, we describe a PCR-based assay that discriminates the wild-type vrn-D1 allele from the Vrn-D1s allele. Collectively, the work described here highlights the potential of utilizing minor hexaploid wheat species for the identification of novel alleles of agronomic importance.

Photoperiod response in wheat is determined to a large extent by the homoeologous series of Photoperiod 1 (Ppd1) genes. In this study, Ppd-A1 genomic sequences from the 5' UTR and promoter region were analysed in 104 accessions of six tetraploid wheat species (Triticum dicoccoides, T. dicoccum, T. turgidum, T. polonicum, T. carthlicum, T. durum) and 102 accessions of six hexaploid wheat species (T. aestivum, T. compactum, T. sphaerococcum, T. spelta, T. macha, T. vavilovii). This data was supplemented with in silico analysis of publicly available sequences from 46 to 193 accessions of diploid and tetraploid wheat, respectively. Analysis of a region of the Ppd-A1 promoter identified thirteen haplotypes, which were divided in two haplogroups. Distribution of the Ppd-A1 haplogroups and haplotypes in wheat species, and their geographical distributions were analysed. Polymerase chain reaction combined with a heteroduplex mobility assay was subsequently used to efficiently discriminate between Ppd-A1 alleles, allowing identification of the Ppd-A1b haplotypes and haplogroups. The causes of anomalous migration of Ppd-A1 heteroduplexes in gels were found to be the localization of mismatches relative to the center of fragment, the cumulative effect of neighbouring polymorphic sites, and the location of mismatches within A/T-tracts. Analysis of the Ppd-A1 5' UTR in hexaploid wheat revealed a novel mutation within the "photoperiod critical" region in a subset of T. compactum accessions. This putative photoperiod insensitive allele (designated Ppd-A1a.4) includes a 684 bp deletion which spans region in common with deletions previously identified in other photoperiod insensitive Ppd1 alleles.

Abstract:The high adaptive potential of modern wheat to a wide range of environmental conditions is determined by genetic changes during domestication. Genetic diversity in VRN1 genes is a key contributor to this adaptability. Previously, the association between the transitions C->T within the fourth and seventh exons of VRN-A1, the distinguishing pair haplotypes Ex4C/Ex4T and Ex7C/Ex7T, and the modulation of such agronomically valuable traits as the vernalization requirement duration, frost tolerance and flowering time of wheat have been shown. However, this polymorphism was analyzed in only a few cultivars of Triticum aestivum L., and not in other wheat species. In the present study, VRN-A1 exon 4 and exon 7 were investigated in six tetraploid and five hexaploid wheat species carrying different VRN-A1 alleles. An allele-specific polymerase chain reaction (PCR) assay was optimized to identify the VRN-A1 exon 7 haplotypes. It was found that polymorphism of the VRN-A1 exon 7 originated in wild tetraploid wheat of Triticum dicoccoides Körn, while the mutant exon 4 of this gene originated later in domesticated hexaploid wheat of T. aestivum. Both these polymorphisms are found in all hexaploid wheat species. Analysis of the VRN-A1 exon 4 and exon 7 haplotype combinations found that intact exon 7 and mutant exon 4 are associated with analogous types of exon 4 and 7, respectively. With the exclusion of the Vrn-A1c (IL369) and Vrn-A1j alleles, identified only in hexaploid wheat, all dominant VRN-A1 alleles carry intact exons 4 and 7 (Ex4C/7C haplotype). The Ex4C/4T/7T haplotype was detected in numerous accessions of hexaploid wheat and is associated with the presence of multiple copies of VRN-A1. Overall, modern domesticated hexaploid wheat T. aestivum includes most possible combinations of the VRN-A1 exon 4 and exon 7 haplotypes among polyploid wheat, which are present in different proportions. This contributes to the high adaptive potential to a broad range of environmental conditions and facilitates the widespread distribution of this species throughout the world.

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