Theoretical and Applied Genetics

, Volume 63, Issue 4, pp 349–360 | Cite as

Chromosome and nucleotide sequence differentiation in genomes of polyploid Triticum species

  • J. Dvořák
  • R. Appels
Article

Summary

The nature of genome change during polyploid evolution was studied by analysing selected species within the tribe Triticeae. The levels of genome changes examined included structural alterations (translocations, inversions), heterochromatinization, and nucleotide sequence change in the rDNA regions. These analyses provided data for evaluating models of genome evolution in polyploids in the genus Triticum, postulated on the basis of chromosome pairing at metaphase I in interspecies hybrids.

The significance of structural chromosome alterations with respect to reduced MI chromosome pairing in interspecific hybrids was assayed by determining the incidence of heterozygosity for translocations and paracentric inversions in the A and B genomes of T. timopheevii ssp. araraticum (referred to as T. araraticum) represented by two lines, 1760 and 2541, and T. aestivum cv. Chinese Spring. Line 1760 differed from Chinese Spring by translocations in chromosomes 1A, 3A, 4A, 6A, 7A, 3B, 4B, 7B and possibly 2B. Line 2541 differed from Chinese Spring by translocations in chromosomes 3A, 6A, 6B and possibly 2B. Line 1760 also differed from Chinese Spring by paracentric inversions in arms 1AL and 4AL whereas line 2541 differed by inversions in 1BL and 4AL (not all chromosomes arms were assayed). The incidence of structural changes in the A and B genomes did not coincide with the more extensive differentiation of the B genomes relative to the A genomes as reflected by chromosome pairing studies.

To assay changing degrees of heterochromatinization among species of the genus Triticum, all the diploid and polyploid species were C-banded. No general agreement was observed between the amount of heterochromatin and the ability of the respective chromosomes to pair with chromosomes of the ancestral species. Marked changes in the amount of heterochromatin were found to have occurred during the evolution of some of the polyploids.

The analysis of the rDNA region provided evidence for rapid “fixation” of new repeated sequences at two levels, namely, among the 130 bp repeated sequences of the spacer and at the level of the repeated arrays of the 9 kb rDNA units. These occurred both within a given rDNA region and between rDNA regions on nonhomologous chromosomes. The levels of change in the rDNA regions provided good precedent for expecting extensive nucleotide sequence changes associated with differentiation of Triticum genomes and these processes are argued to be the principal cause of genome differentiation as revealed by chromosome pairing studies.

Key words

Chromosomes Nucleotides Evolution Polyploids Triticum Heterochromatin Wheat 

Preview

Unable to display preview. Download preview PDF.

Unable to display preview. Download preview PDF.

Literature

  1. Appels, R.; Dvořák, J. (1982): The wheat ribosomal DNA spacer region: its structure and variation in populations and among species. Theor. Appl. Genet. 63, 337–348Google Scholar
  2. Coen, E.S.; Thoday, J.M.; Dover, G. (1982): Rate of turnover of structural variants in the rDNA gene family of Drosophila melanogaster. Nature 295, 564–568Google Scholar
  3. Dhaliwal, H.S.; Johnson, B.L. (1982): Diploidization and chromosome pairing affinities in the tetraploid wheats and their putative amphiploid progenitor. Theor. Appl. Genet. 61, 117–123Google Scholar
  4. Dvořák, J.; McGuire, P.E. (1981): Nonstructural chromosome differentiation among wheat cultivars, with special reference to differentiation of chromosomes in related species. Genetics 97, 391–414Google Scholar
  5. Feldman, M. (1966): Identification of unpaired chromosomes in F1 hybrids involving Triticum aestivum and T. timopheevii. Can. J. Genet. Cytol. 8, 144–151Google Scholar
  6. Gerlach, W.L. (1977): N-banded karyotypes of wheat species. Chromosoma 62, 49–56Google Scholar
  7. Gerlach, W.L.; Bedbrook, J.R. (1979): Cloning and characterization of ribosomal DNA from wheat and barley. Nucleic Acids Res. 7, 1896–1885Google Scholar
  8. Gill, B.S.; Kimber, G. (1974): Giemsa C-banding and the evolution of wheat. Proc. Natl. Acad. Sci. USA 71, 4086–4090Google Scholar
  9. Johnson, B.L.; Dhaliwal, H.S. (1978): Triticum urartu and genome evolution in the tetraploid wheats. Am. J. Bot. 65, 907–918Google Scholar
  10. Kihara, H. (1940): Verwandtschaft der Aegilops-Arten im Lichte der Genomanalyse. Ein Überblick. Züchter 12, 49–62Google Scholar
  11. Kihara, H. (1963): Interspecific relationship in Triticum and Aegilops. Seiken Ziho 15, 1–12Google Scholar
  12. Lilienfeld, F.A. (1951): Kihara. Genome analysis in Triticum and Aegilops. X. Concluding remarks. Cytologia 16, 101–123Google Scholar
  13. McFadden, E.R.; Sears, E.R. (1946): The origin of Triticum spelta and its free-threshing hexaploid relatives. J. Hered. 37, 81–89Google Scholar
  14. Peacock, W.J.; Gerlach, W.L.; Dennis, E.S. (1981): Molecular aspects of wheat evolution repeated DNA sequences. In: Wheat science-today and tomorrow (eds. Evans, L.T.; Peacock, W.J.). Cambridge: Cambridge University PressGoogle Scholar
  15. Sachs, L. (1953): Chromosome behaviour of species hybrids with Triticum timopheevi. Heredity 7, 49–58Google Scholar
  16. Tanaka, M.; Kawahara, T.; Saro J. (1979): The evolution of wild tetraploid wheats, pp. 73–80. New Delhi: Proc. 5th Int. Wheat Genet. Symp.Google Scholar
  17. Zohary, D.; Feldman, M. (1962): Hybridization between amphiploids and the evolution of polyploids in the wheat (Aegilops-Triticum) group. Evolution 16, 44–61Google Scholar

Copyright information

© Springer-Verlag 1982

Authors and Affiliations

  • J. Dvořák
    • 1
  • R. Appels
    • 2
  1. 1.Department of Agronomy and Range ScienceUniversity of CaliforniaDavisUSA
  2. 2.Division of Plant IndustryCSIROCanberra CityAustralia

Personalised recommendations