Transgenerationally Precipitated Karyotypic Variation And Phenotypic Diversity In A Synthetic Allotetraploid Wheat With Genome AADD

Each species has a karyotype of its own chromosome number and structure,which is the phenotype of the organism at the chromosomal level,and it is inherently unstable.Polyploidy or whole genome duplication(WGD)has played a pervasive and significant role in the evolution of all eukaryotes.The short-term effects of polyploidization can cause the changes of cell size,body size,genomic stability and gene expression.The long-term effects can guide evolutionary transitions and increase genomic complexity.All the flowering plant lineages have undergone multiple rounds of WGD events.WGD is a huge driving force for rapid karyotypic reconfiguration,especially the oneset of polyploidization.At the initial stage of polyploidy,due to the immediate increasing dosages of chromosomes,the probability of meiosis abnormal becomes greater.Therefore,a large number of homoeologous recombination at metaphase I and lagging chromosomes at anaphase appear,resulting in aneuploidy and structural translocation in polyploid progenies.With the continuous development of sequencing technology,people are becoming more and more enthusiastic about the research at sequence level.However,chromosomes as the basic carrier of genetic materials,any mutation on them(e.g.the SNP sites mutation,large fragments repeat or loss)may cause fatal harm to the organisms.For example,many human diseases and cancers are caused by the unbalanced copy number of chromosome.The detrimental effects of aneuploidy or structural variation on phenotypes(i.e.seed setting)have also been reported in plants.Therefore,the studies at chromosome level remains to be further explored.Wheat,one of the most important food crops in the world,provides 20% of calories and protein for human nutrition.Wheat has undergone two rounds of allopolyploidization and achieved a magnificent turn from weeds to grain crops.The large size of wheat genome(close to 80% of repeat sequences)adds the difficulty to analysis at sequence level,but it is well suited for the cytological chromosome observation.Therefore,polyploid wheat is an ideal material to study the proliferation of the karyotypic heterogeneity and phenotypic diversity of the newly formed allopolyploidy at the population level.Here,we reported an artificially constructed allotetraploid wheat with a genome combination of AADD,which contains two subgenomes in hexaploid bread wheat.We analyzed a large scale of karyotypic heterogeneity that exhibited phenotypic diversity.Specifically,we showed that(1)a large number of organismal level karyotypic heterogeneity was precipitated during selfing of the random offspring from a single euploid founder after 12 consecutive generations;(2)there were the large tendency of chromosomal gain or loss and structural variation between the A-and D-subgenome and among 14 chromosomes;(3)majority of the chromosome numerical and structural variation were concurrent,presumably due to mutual emergency response and functional constraints;(4)purposed and continuous selection of euploid generations did not increase the karyotypic stabilization of offspring;(5)the extent of karyotypic variation correlated with variability of phenotypic diversity.Taken together,our results demonstrated that allopolyploidization can catalyze rampant and transgenerationally heritable karyotypic heterogeneity,and drive population-level phenotypic diversification.This provided a new empirical support for the theory that whole genome duplication can enhance biologic organismal evolvability.