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.
Highlights
Wheat was one of the first crops to be domesticated and comprises a key source of raw material for the food and processing industry
We identify the different combinations of the VRN-A1 exon 4 and exon 7 haplotypes to shed light on their origin, divergence and distribution in modern domesticated wheat species
Using a designed primer set, 319 bp polymerase chain reaction (PCR) fragments detect the haplotype of the wild type (Ex7C), while 332 bp fragments indicate the mutant exon 7 of VRN-A1
Summary
Wheat was one of the first crops to be domesticated and comprises a key source of raw material for the food and processing industry. Triticum dicoccum Schrank (BBAA genomes) was domesticated approximately 10,000 years ago from wild emmer T. dicoccoides. In turn, arose the free-threshing tetraploid wheat (T. durum) [1]. Hexaploid wheat (T. aestivum, BBAADD genomes) was derived from the hybridization of tetraploid wheat with the goat grass Aegilops tauschii Coss. Following the domestication of wheat, the cultivation of this crop began to spread widely beyond the confines of the fertile crescent [1]. The culmination of this trend means that currently more of Agronomy 2018, 8, 156; doi:10.3390/agronomy8080156 www.mdpi.com/journal/agronomy
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