(Gaa)N Microsatellite As An Indicator Of The A Genome Reorganization During Wheat Evolution And Domestication

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, T. boeoticum Boissier, 1874 and T. monococcum Linnaeus, 1753) and polyploid wheat species representing two evolutionary lineages, Timopheevi (T. timopheevii (Zhukovsky) Zhukovsky, 1934 and T. zhukovskyi Menabde & Ericzjan, 1960) and Emmer (T. dicoccoides (Kornicke ex Ascherson & Graebner) Schweinfurth, 1908, T. durum Desfontaines, 1798, and T. aestivum Linnaeus, 1753) using a new cytogenetic marker - the pTm30 probe cloned from T. 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 T. 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 T. monococcum. Among three wild emmer (T. 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 T. dicoccoides were retained in T. durum and T. 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 T. monococcum are undetectable in the A(b) genome of T. 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.