Differential Expression of Structural and Copy Number Variants of the <i>Vernalization‐A1b</i> Allele in Hexaploid Wheat ( <i>Triticum</i> spp)

ABSTRACT The earliness of spring wheat cultivars is mainly determined by the VRN‐A1 gene. Among the dominant alleles of this gene, the Vrn‐A1b is the next most common in bread wheat ( Triticum aestivum ssp. aestivum L.) after VRN‐A1 a but is the first in spelt ( Triticum aestivum ssp. spelta L.). Structural and copy number variation of Vrn‐A1b spans a wide range of poorly studied variants of this allele, which represent an attractive resource for wheat breeding. Here, the cultivars of common and spelt wheat carrying Vrn‐A1b were screened for copy number and structural variants of this allele. The most frequent haplotype in common wheat was Vrn‐A1b.1/b.4 , containing a 68.5‐kb segmental duplication on chromosome 5A. In T. spelta , duplication of vrn‐A1b.3 , but not Vrn‐A1b.2 and Vrn‐A1b.6, was shown. Expression dynamics of the Vrn‐A1b structural variants were analysed to assess their flowering‐promoting potencies. Evidence confirming the dominant type of alleles Vrn‐A1b.1 , Vrn‐A1b.1/b.4 , Vrn‐A1b.2 , Vrn‐A1b .6 and the recessive‐type vrn‐A1b.3 was obtained. The highest transcriptional activity was shown for the Vrn‐A1b.2 and Vrn‐A1b .6 alleles in spelt and duplicated Vrn‐A1b.1 in common wheat, whereas the lowest was for vrn‐A1b.3 . In common wheat at three‐leaf stage, the Vrn‐A1b.1/b.4 was expressed up to 60 times weaker than the duplicated Vrn‐A1b.1 but was at least 5 times stronger than vrn‐A1b.3 . Comparative analysis of the expression of Vrn‐A1b.1/b.4 and a single copy of Vrn‐A1b.1 in club wheat ( Triticum aestivum L. ssp. compactum Host) found a progressive increase in the transcriptional activity of the former, resulting in a 22‐fold difference between the haplotypes at the four‐leaf stage, which correlated with their earliness. Because of the strong contrasting impact on the growth habit and substantial difference in the expression, the need for precise identification of structural variants of the Vrn‐A1b allele during wheat genotyping is justified. The data presented can be useful for breeding genotypes with contrasting development rates.