(GAA)n microsatellite as an indicator of the A genome reorganization during wheat evolution and domestication.

Elena A Salina,Ekaterina M Sergeeva,Ekaterina D Badaeva,Irina G Adonina,Nadezhda V Petrash,Nikolay P Goncharov

doi:10.3897/compcytogen.v9i4.5120

Abstract

Although the wheat A genomes have been intensively studied over past decades, many questions concerning the mechanisms of their divergence and evolution still remain unsolved. In the present study we performed comparative analysis of the A genome chromosomes in diploid (Triticum urartu Tumanian ex Gandilyan, 1972, Triticum boeoticum Boissier, 1874 and Triticum monococcum Linnaeus, 1753) and polyploid wheat species representing two evolutionary lineages, Timopheevi (Triticum timopheevii (Zhukovsky) Zhukovsky, 1934 and Triticum zhukovskyi Menabde & Ericzjan, 1960) and Emmer (Triticum dicoccoides (Körnicke ex Ascherson & Graebner) Schweinfurth, 1908, Triticum durum Desfontaines, 1798, and Triticum aestivum Linnaeus, 1753) using a new cytogenetic marker – the pTm30 probe cloned from Triticum monococcum genome and containing (GAA)56 microsatellite sequence. Up to four pTm30 sites located on 1AS, 5AS, 2AS, and 4AL chromosomes have been revealed in the wild diploid species, although most accessions contained one–two (GAA)n sites. The domesticated diploid species Triticum monococcum differs from the wild diploid species by almost complete lack of polymorphism in the distribution of (GAA)n site. Only one (GAA)n site in the 4AL chromosome has been found in Triticum monococcum. Among three wild emmer (Triticum dicoccoides) accessions we detected 4 conserved and 9 polymorphic (GAA)n sites in the A genome. The (GAA)n loci on chromosomes 2AS, 4AL, and 5AL found in of Triticum dicoccoides were retained in Triticum durum and Triticum aestivum. In species of the Timopheevi lineage, the only one, large (GAA)n site has been detected in the short arm of 6At chromosome. (GAA)n site observed in Triticum monococcum are undetectable in the Ab genome of Triticum zhukovskyi, this site could be eliminated over the course of amphiploidization, while the species was established. We also demonstrated that changes in the distribution of (GAA)n sequence on the A-genome chromosomes of diploid and polyploid wheats are associated with chromosomal rearrangements/ modifications, involving mainly the NOR (nucleolus organizer region)-bearing chromosomes, that took place during the evolution of wild and domesticated species.

Highlights

The genus Triticum Linnaeus, 1753 comprises species at different ploidy levels, from diploid to hexaploid
We demonstrated that changes in the distribution of (GAA)n sequence on the A-genome chromosomes of diploid and polyploid wheats are associated with chromosomal rearrangements/ modifications, involving mainly the NOR-bearing chromosomes, that took place during the evolution of wild and domesticated species
As is currently assumed by the majority of researchers, tetraploid Emmer (T. dicoccoides ((Körnicke ex Ascherson & Graebner) Schweinfurth, 1908, T. durum Desfontaines, 1798, etc. genome BBAA) and Timopheevi (T. araraticum Jakubziner, 1947, T. timopheevii, and T. militinae Zhukovsky & Miguschova, 1969, genome GGAtAt) wheats occurred as a result of hybridization between the ancestral forms of Ae. speltoides Tausch, 1837 as a maternal parent and T. urartu Tumanian ex Gandilyan, 1972, as a paternal parent (Dvorak et al 1988, Tsunewaki 1996, Huang et al 2002)

Summary

Introduction

The genus Triticum Linnaeus, 1753 comprises species at different ploidy levels, from diploid to hexaploid. Genome BBAA) and Timopheevi (T. araraticum Jakubziner, 1947, T. timopheevii, and T. militinae Zhukovsky & Miguschova, 1969, genome GGAtAt) wheats occurred as a result of hybridization between the ancestral forms of Ae. speltoides Tausch, 1837 as a maternal parent and T. urartu Tumanian ex Gandilyan, 1972, as a paternal parent (Dvorak et al 1988, Tsunewaki 1996, Huang et al 2002) Both evolutionary lineages of the tetraploid wheats originated via hybridization of closely related parental forms, their emergence occurred independently at different times and probably in different places. The origin of the tetraploid T. dicoccoides is dated back to over 500 TYA, versus T. araraticum, dated back to 50–300 TYA (Mori et al 1995, Huang et al 2002, Levy and Feldman 2002)

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