Sporogenesis Of Hybrids Between Hexaploid Wheat And Rye And The Identifications Of Chromosome Constitution Of Progenies

Polyploidization has played a crucial role in the evolution of higher plants. Wide hybridization, the first step for the origination of allopolyploids, brings divergent genomes from different species together into an amphihaploid hybrid. Gametes produced by hybrids without homologous chromosomes are often sterile that hinders gene transferring from alien species into wheat genome. Previous studies found that unreduced gamete could enable chromosomes to double spontaneously, allowing exogenetic germplasm to integrate into wheat genome.In the present study, we used classical cytogenetics and molecular cytogenetics techniques (GISH, genomic in situ hybridization and FISH, fluorescence in situ hybridization) to observe meiotic chromosome behaviors of pollen mother cells in different F1 hybrids of hexaploid wheat with genes for unreduced gamete formation and rye, and to identify their chromosome constitutions of F2S. We analyzed the formation pattern of unreduced gametes and its effectiveness of fixing translocated chromosome. The main results are as followed:We found that chromosomes of F1 hybrids were mainly in univalents although homoeologous chromosome pairing occurred at varied frequencies among the analyzed 13 hybrid combinations of hexaploid wheat with rye Qinling, leading to the production of bivalents and trivalents. The number of cross knots of hybrid J91 involved in synthetic hexaploid wheat (SHW) is significantly lower than others involved in SHW-derived lines, indicating that the pairing ability of wide hybrids is dependent on genetic backgrounds.We identified the chromosome constitution of selling F2 plants of SHW Langdon X AS65 with rye using genomic in situ hybridization technique. The total number of chromosomes in 5 plants ranged from 45 to 56 that were amphidiploids and partial amphidiploids. Centromeric behaviors were further observed in their F1 haploid hybrids using the special sequence PrCEN-1 of rye centromere as FISH probe. Our observations showed that there only existed a single meiotic division, in which sister chromatids separated and resulted in unreduced gametes. The combination of unreduced gametes realized the chromosome doubling of F1 haploid hybrids spontaneously. We identified the chromosome constitution of root tip cells in 29 F2 plants. The total number of chromosome varied from 37-56. The range of wheat chromosome number is 32-42, and 5-14 for rye chromosome. There were distinctive differences in the chromosome constitutions of F2 plants between hybrids of SHW and SHW-derived lines with rye, indicating that different genetic background affected the formation of unreduced gamete. In addition, we detected a high frequency of translocations in offspring, implying that translocations could transfer from F1 haploid hybrids to F2 through unreduced gametes.Chromosome pairing of pollen mother cells at metaphase I in F2 plants had substantial univalents with a wide range from 5.22 to 16.07although a lot of rod and ring bivalents and a low frequency of trivalents and tetravalents were observed. Cytological abnormal phenomena were observed, for example, chromosome lagging, chromosome bridges and micro-nucli. Using GISH, we found that rye chromosomes were preferential to lag behind wheat chromosomes in meiosis. Besides, there were two distinct types of rye chromosome behaviors:sister chromatids of rye separated and moved to bipolar cells at anaphase I or sister chromatids of rye joined by a centromere migrated to one polar together at anaphase I.