Characterization Of Allopolyploidization Mediated By Unreduced Gametes In Triteceae

Polyploidization is an important drive force of plant evolution.Triticeae is generally considered to originate from interspecific or intergeneric hybridization,followed by genome doubling.Fusion of unreduced gametes is usuanlly believed to be the main pathway during these events.Unreduced gametes have been widely reported in F₁ hybrids of wheat?mostly tetraploid wheat?and related species and wheat polyhaploid,and thus plentiful allopolyploidy stocks have been synthesized using this method.Therefore,it is of great importance to explore mechanisms of unreduced gametes formation in distant hybridization materials by the enrichment and application of tetralpoid wheat stocks.Tracking the polyploidization of newly synthesized hexaploid wheat and triticale would assist us to have a better understanding of Triticeae's evelotionary process.It will be also meaningful to synthesize more newly allopolyploidy species for wheat improvement.We developed 12 double ditelosomics in durum DR147's background,and discriminated these lines by molecular and cytological techniques?FISH and molecular markers?,and some distinct genetic traits of tetraploid wheat were indicated,such as awnless control.Furthermore,F₁ hybrids of these double ditelosomics and rye were isolated by embryo rescue,and GISH and FISH were applied to track the meiosis of these hybrids.Then,the pathways of unreduced gametes formation and effects of different telosomes on the F₁ hybrids were implied.Moreover,molecular and cytological methods were employed to trace the synthesized hexaploid wheat and triticale mediated by unreduced gametes,and plentiful chromosome-level,sorage-protein-level and sequence-level variations were assayed during the polyploidization.1.12 double ditelosomics in durum DR147's background?excluding dDt2 B and dDt3A?were developed.According to the FISH karyotype of DR147,established by using pAsl and pHvG38 as probes,pAsl,pHvG38 and centromere-specific probe?6C6?were combined to distinguish the double ditelosomics and they were then accurately designated.Most of the double ditelosomics were similar to DR147 while dDt6 B showed distinct awnless phenotype,which arised from the presence of awning inhibitor B2 located in 6BL retained from hexaploid wheat Chinese spring.B2 locus was proved to be partial dominant and essential for the awnless phenotype.Then,B2 locus was anchored to a region between 6BL-5 and the distal boundary of 6BL-6's interstitial deletion,near to three markers-Xwmc539,Xgpw5130 and Xwmc748.2.F₁ hybrids of DR147 or double ditelosomics and rye were isolated by embryo rescue,and differed meiosis processes were indicated in different F₁ plants.The telosomes of 1A,6A,3B,4B obviously promoted the paring between homeologous chromosomes,and the telosomes of 7B influenced the condensity of chromosomes.First division restitution,preseparation of chromatids and premature of cytokinesis might be the pathways of unreduced gametes formation in tetraploid wheat × rye.The centromeres of univalents showed biorientation at metaphase of first meiotic divison in some restituded cells.The equational diads were confirmed to be unreduced meiotic products by FISH using centromere-specific probes.Thus,these researches provided solid evidence on meiosis of F₁ hybrids of tetraploid wheat × rye.3.Synthesized hexaploid wheat NA0928 population was developed by crossing T.dicoccum MY3478 and Ae.tauschii SY41 mediated by unreduced gametes,and then the S0-S3 generations of NA0928 were assayed by detailed cytological and microsatellite techniques.Plentiful chromosomal structural changes or microsatellite variations were assyed in the early generations of newly synthesized hexaploid wheat NA0928,including aneuploidy with whole-chromosome loss or gain,aneuploidy with telosome,chromosome-specific repeated sequence elimination?indicated by FISH?and microsatellite sequence elimination?indicated by sequencing?,and many kinds of variations have not been previously reported.In S0 and S1 generation,the mutation rates were 3.17 × 10-2 and 8.85 × 10-3,respectively.Additionally,we reported a new germplasm-T.dicoccum accession MY3478 with excellent trait of unreduced gametes formation,and then succeeded to transfer resistance genes from Ae.tauschii SY41 to synthesized allohexaploid wheat NA0928,which would be valuable resistance resources for wheat improvement.Hence,this research not only demonstrated the fierce genomic shock accompanying the polyploidization of newly synthesized hexaploid wheat,but also contributed potential resistance resources to wheat improvement.4.Two hexaploid triticales?namely N9116 H and N9116M?with great morphologic divergence were derived from common wheat cultivar M8003?Triticum aestivum L.?× Austrian rye?Secale cereale L.?.Sequential FISH and GISH karyotyping revealed that Dgenome chromosomes were completely eliminated and the whole A-genome,B-genome and R-genome chromosomes were retained in both lines.Furthermore,altered chromosomes including 5A and 7B were detected in both triticales and additionally altered 5B,7A chromosome and restructured chromosome 2A was assayed in N9116 H and N9116 M,respectively,even after selfing for several decades.Besides,meiotic asynchrony was displayed and a variety of storage protein variations were assayed,especially in the HMW/LMW-GS region and secalins region of both triticales.This study confirmed that R genome of rye could affect the stability of common wheat's genomes and whole D-genome chromosomes could be preferentially eliminated in the hybrid of common wheat × rye.“Genome shock” was accompanying the allopolyploidization of nascent triticales,and great morphologic divergence might result from the genetic variations,such as chromosomal structure alterations and function differences of storage proteins.Moreover,both triticales exhibited high resistance for powdery mildew and stripe rust and potential for wheat improvement.