Genome size in natural and synthetic autopolyploids and in a natural segmental allopolyploid of several Triticeae species

Eilam, T.; Anikster, Y.; Millet, E.; Manisterski, J.; Feldman, M.
March 2009
Genome;Mar2009, Vol. 52 Issue 3, p275
Academic Journal
Nuclear DNA amount (1C) was determined by flow cytometry in the autotetraploid cytotype of Hordeum bulbosum, in the cytologically diploidized autotetraploid cytotypes of Elymus elongatus, Hordeum murinum subsp. murinum and Hordeum murinum subsp. leporinum, in Hordeum marinum subsp. gussoneanum, in their progenitor diploid cytotypes, and in a newly synthesized autotetraploid line of E. elongatus. Several lines collected from different regions of the distribution area of every taxon, each represented by a number of plants, were analyzed in each taxon. The intracytotype variation in nuclear DNA amount of every diploid and autotetraploid cytotype was very small, indicating that no significant changes have occurred in DNA amount either after speciation or after autopolyploid formation. The autotetraploid cytotypes of H. bulbosum and the cytologically diploidized H. marinum subsp. gussoneanum had the expected additive amount of their diploid cytotypes. On the other hand, the cytologically diploidized autotetraploid cytotypes of E. elongatus and H. murinum subsp. murinum and H. murinum subsp. leporinum had considerably less nuclear DNA (10%-23%) than the expected additive value. Also, the newly synthesized autotetraploid line of E. elongatus showed similar reduction in DNA as its natural counterpart, indicating that the reduction in genome size occurred in the natural cytotype during autopolyploidization. It is suggested that the diploid-like meiotic behavior of these cytologically dipolidized autotetraploids is caused by the instantaneous elimination of a large number of DNA sequences, different sequences from different homologous pairs, leading to differentiation of the constituent genomes. The eliminated sequences are likely to include those that participate in homologous recognition and initiation of meiotic pairing. A gene system determining exclusive bivalent pairing by utilizing the differentiation between the two groups of homologues has been presumably superimposed on the DNA reduction process. Le contenu en ADN nucléaire (1C) a été déterminé par cytométrie en flux chez les cytotypes suivants : le cytotype autotétraploïde de l&x2019;Hordeum bulbosum, les cytotypes autotétraploïdes diploïdisés (formant principalement des bivalents) de l&x2019;Elymus elongatus, des Hordeum murimum subsp. murinum et Hordeum murimum subsp. leporinum, des Hordeum marinum subsp. gussoneanum, les cytotypes diploïdes des espèces progénitrices et d&x2019;un E. elongatus autotétraploïde nouvellement synthétisé. Plusieurs lignées provenant des différentes régions de l&x2019;aire de distribution de ces taxons, chacune représentée par plusieurs plantes, ont été analysées pour chaque taxon. La variation pour le contenu en ADN nucléaire au sein d&x2019;un cytotype était très faible chez tous les cytotypes diploïdes et autotétraploïdes, indiquant qu&x2019;aucun changement important n&x2019;était survenu après la spéciation ou la formation d&x2019;un autopolyploïde. Les cytotypes autotétraploïdes de l&x2019;H. bulbosum et de l&x2019;H. marinum subsp. gussoneanum diploïdisé présentaient la quantité attendue suite à l&x2019;addition des cytotypes diploïdes. Par contre, les cytotypes diploïdisés de l&x2019;E. elongatus et des H. murinum subsp. murinum et H. murium subsp. leporinum avaient un contenu en ADN nucléaire nettement moins grand (de 10% à 23% moins) que la somme attendue. De plus, la lignée autotétraploïde nouvellement synthétisée de l&x2019;E. elongatus a affiché une réduction semblable à celle observée chez son pendant naturel ce qui indique que la réduction de la taille du génome serait survenue lors de l&x2019;autopolyploïdisation chez le cytotype naturel. Les auteurs suggèrent que le comportement méiotique de type diploïde chez les autotétraploïdes diploïdisés est causé par une élimination instantanée d&x2019;un grand nombre de séquences, diverses séquences chez différentes paires de chromosomes homologues, menant ainsi à la différenciation des génomes constitutifs. Il est probable que l&x2019;on compte parmi les séquences éliminées celles qui participent à la reconnaissance des homologues à l&x2019;initiation de l&x2019;appariement méiotique. Un système génétique entraînant un appariement exclusivement sous forme de bivalents moyennant la différenciation des deux groupes d&x2019;homologues se seraient vraisemblablement superposée au processus de réduction de la taille du génome.


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