Studies On Molecular Phylogeny And Cytogenetics Of Tetraploid Wheat

Tetraploid wheat is an important group within the genus Triticum L.The group comprise of two allopolyploid species:Triticum turgidum L.and T.timopheevii Zhuk.Triticum turgidum(AABB,2n = 4x = 28)consists of one wild type and eight cultivars.Triticum timopheevii(AAGG,2n = 4x = 28)comprises one wild subspecies and one cultivated subspecies.Tetraploid wheat,as a closely related species of T.aestivum L,has many excellent traits,such as:pests and diseases resistance,lodging resistance and salt tolerance.However,the classification,origin and evolution of tetraploid wheat have still remained in debate,which is confined to part of tetraploid wheat.The objectives of the present paper were:(1)to reconstruct phylogenetic progress of tetraploid wheat basing on DMC1 gene and ITS sequence,to estimate phylogenetic relationships,and to futherly examine the origin and evolution of tetraploid wheat;(2)to study the chromosomal differentiation,polymorphism and the phylogenetic relationship of tetraploid wheat by fluorescence in situ hybridization analysis of pSc119.2 and pTa535 probes.The results of this study provided some insights into the origin and evolution of tetraploid wheat.The main results showed as follows:1.A total of 61 materials of tetraploid wheat and possibly diploid donor species were studied on phylogeny using DMC1 sequence.Based on neighbor-joining approaches and maximum-likelihood,the phylogenetic trees were constructed using the whole DMC1 gene sequence.The results showed that sequences from the A genome of tetraploid wheat were clustered with T.urartu,and the sequences from the B genome and G genome were grouped with Aegilops speltoides.These results indicated that the donor of the A genomes was T.urartu rather than T.monococcum.B and G genome of tetraploid wheat derived from Ae.speltoides.The tetraploid wheat of the hulled traits formed a subclade,and the naked tetraploid wheat were clustered into another subclade,indicating that the relationship of naked tetraploid wheat were phylogenetically related and the relationship of hulled tetraploid wheat were closely related.2.The internal transcribed spacer(ITS)of nuclear ribosomal DNA had also been used to study the evolution of two tetraploid wheat species.In this study,except T.turgidum ssp.carthlicum accession PI532494,different ITS sequences from an individual were only found in the tetraploid species,indicating that these repeats were not independent in evolution but were affected by a concerted force or by molecular drive.In the present study,phylogenetic analysis showed that T.turgidum ssp.dicoccoides from the western population were clustered together with the hulled tetraploid wheat,which indicated that the western population was involved in the formation and evolution of the hulled tetraploid wheat;In the naked tetraploid wheat,T.turgidum ssp.polonicum,T.turgidum ssp.carthlicum and T.turgidum ssp.turgidum from Fertile Crescent were clustered together with hulled tetraploid wheat,showing that the origin of these three tetraploid wheat could occur in the Fertile Crescent;T.turgidum ssp.durum and T.turgidum ssp.turanicum were not clustered with T.turgidum ssp.dicoccon,which suggested that the formation of T.turgidum ssp.durum and T.turgidum ssp.turanicum were not related to T.turgidum ssp.dicoccon,but related to the remaining tetraploid wheat.3.Fluorescence in situ hybridization(FISH)was used to detect tetraploid wheat using probes pTa535 and pSc119.2.The results showed that the signal loci of tetraploid wheat were abundant and polymorphic;In clustering analysis,T.turgidum ssp.dicoccoides did not clustered with T.turgidum ssp.dicoccon,T.turgidum ssp.paleocolchicum,and T.turgidum ssp.ispahanicum,and the signal sites had undergone great variation.These results indicated that the differentiation was obvious after the formation of these three hulled wheat;T.turgidum and T.timopheevii were distributed in two different branches,and they hold the same parents in the phylogenetic tree of the DMC1 gene.The results showed that T.turgidum and T.timopheevii might have simultaneously originated from a common ancestral tetraploid species and a greater genetic differentiation appeared in the evolution process.