Molecular Cytogenetic Analysis Of Wheat-rye 1RS/6AS Translocation

Common wheat (Triticum aestivum L.,2n=6x=42, AABBDD), one of the three major food crops, is important for ensuring food security. Genetic variation is the basis of genetic improvement of wheat. Since the origin and domestication of common wheat has led to the genetic bottleneck and the modern breeding process has further narrowed its genetic diversity, broadening the genetic basis of wheat is always an important task. Distant hybridization is one of the most used techniques to import excellent genes from wheat-related species into wheat. Rye (Secale cereale L.,2n=2x=14, RR) is widely used as a genetic resource for wheat improvement because it contains a variety of desirable traits, such as disease resistance and stress tolerance. Wheat-rye hybridization induced more genetic variations than other wheat-related species hybridization and thus wheat-rye hybridization are an excellent mode to investigate genetic outcomes of distant hybridization.In this study, we developed selfed progenies of hybrids between wheat lines 990, derived from synthetic hexaploid wheat, and rye cultivar Qinling. Their chromosome composition were then analyzed using genomic in situ hybridization (GISH) and fluorescence in situ hybridization (FISH) to screen new wheat-rye translocation lines. Meanwhile, we study the variation of 45S rDNA sites using FISH and gene cloning technology. The main results are as follows:A wheat-rye translocation chromosome was detected in the root tip cells of the F7 plant HM201-202-1-10 by GISH using rye genomic DNA as a probe. The chromosome constitution of its derived 40 F8 seeds were further analyzed using GISH and FISH. Their chromosome number varied from 41 to 43, including 11 seeds containing one wheat-rye translocation, four (HM201-201-1-10-8, HM201-201-1-10-29, HM201-201-1-10-33, HM201-201-1-10-35) containing a pair of wheat-rye translocations, and the remainders having no wheat-rye translocation. The terminal and sub-terminal regions of the translocated rye arm exhibited pScl 19.2 and 45S rDNA (pTa71) signals, respectively. The terminal of wheat arm had two pTa535 signals. These results indicated that this translocation was 1RS/6AS non-homologous translocation.FISH analysis using pTa71 as the probe revealed that 45S rDNA signals appeared on the 1BS and 6BS secondary constriction and the 5DS terminal of wheat parent 990 and the IRS secondary constrictions of rye parent. Besides these signals, we detected a 45S rDNA (pTa71) signal on the terminal of 3DS chromosome was in their hybrid progenies of HM201-202-1-10. This suggested that wheat-rye hybridization induced the movement of 45S rDNA. Only two wheat lines were previously reported to have 45S rDNA signal on 3DS. One is common wheat Wichita. The other is 6V/6A substitution line. We speculated that the specific chromosome constitution of 3DS is favor to the de novo forming of 45S rDNA.Rye parent and the wheat-rye derivative HM201-202-1-10-36 containing the 45S rDNA (pTa71) signal on 3DS but without 1R wereused to clone ITS sequences of 45S rDNA. All the 20 rye ITS clones were identical, with 659 bp in length. We did not detected the rye ITS sequence from the analyzed 38 ITS clones from HM201-202-1-10-36. We hence suggested that the 45S rDNA on 3DS was not moved from rye chromosome but from a wheat chromosome. It is unclear, however, which wheat chromosome is the donor of 45S rDNA on 3DS.