Abstract
Dramatic changes occasionally occur in intergenic regions leading to genomic alterations during speciation and will consequently obscure the ancestral species that have contributed to the formation of allopolyploid organisms. The S genome of five species of section Sitopsis of genus Aegilops is considered to be an origin of B-genome in cultivated tetraploid and hexaploid wheat species, although its actual donor is still unclear. Here, we attempted to elucidate phylogenetic relationship among Sitopsis species by performing RNA sequencing of the coding regions of each chromosome. Thus, genome-wide polymorphisms were extensively analyzed in 19 accessions of the Sitopsis species in reference to the tetraploid and hexaploid wheat B genome sequences and consequently were efficiently anchored to the B-genome chromosomes. The results of our genome-wide exon sequencing and resultant phylogenetic analysis indicate that Ae. speltoides is likely to be the direct donor of all chromosomes of the wheat B genome. Our results also indicate that the genome differentiation during wheat allopolyploidization from S to B proceeds at different speeds over the chromosomes rather than at constant rate and recombination could be a factor determining the speed. This observation is potentially generalized to genome differentiation during plant allopolyploid evolution.
Highlights
Common wheat (Triticum aestivum L., genome constitutionAABBDD), a major food crop, is an allohexaploid species derived via allopolyploid speciation through interspecific crossing between cultivated tetraploid wheat Triticum turgidum L. (AABB) and its diploid relative, Aegilops tauschii Coss. (DD).[1,2,3,4] The cultivated tetraploid form was domesticated from the wild tetraploid wheatT. turgidum subspecies dicoccoides (AABB), which was thought toC The Author(s) 2019
The phylogenetic relationship between the B and S genomes of section Sitopsis should be reconsidered based on the polymorphisms of each limited chromosomal region as well as those covering the entire chromosomal regions of the B and S
The objectives of the present study were to (i) identify genome-wide polymorphisms in the Sitopsis genomes, (ii) elucidate the phylogenetic relationship among Sitopsis species, and (iii) determine the wheat B-genome origin based on genome-wide polymorphisms anchored putatively to each chromosome of the B genome
Summary
Common wheat (Triticum aestivum L., genome constitutionAABBDD), a major food crop, is an allohexaploid species derived via allopolyploid speciation through interspecific crossing between cultivated tetraploid wheat Triticum turgidum L. (AABB) and its diploid relative, Aegilops tauschii Coss. (DD).[1,2,3,4] The cultivated tetraploid form was domesticated from the wild tetraploid wheatT. turgidum subspecies dicoccoides (AABB), which was thought toC The Author(s) 2019. AABBDD), a major food crop, is an allohexaploid species derived via allopolyploid speciation through interspecific crossing between cultivated tetraploid wheat Triticum turgidum L. T. turgidum subspecies dicoccoides (AABB), which was thought to. B-genome origin of common wheat divergence is thought to be a result of polyploidization events affecting B-genome evolution.[34] the phylogenetic relationship between the B and S genomes of section Sitopsis should be reconsidered based on the polymorphisms of each limited chromosomal region as well as those covering the entire chromosomal regions of the B and S genomes
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