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

Abstract

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.

Natural Pathways to Polyploidy in Plants and Consequences for Genome Reorganization

“…homologous recombination) during the first generations of the diploidization process [Ma and Gustafson, 2005]. This is consistent with the elimination of sequences from homoeologous chromosome regions in both auto-and allopolyploids during cytological diploidization [Eilam et al, 2009[Eilam et al, , 2010Feldman et al, 2012]. Nevertheless, the hypothesis that restructuring is adaptive, improving the fertility of neopolyploids, largely remains to be tested.…”

Nuclear DNA Amounts of Mulberries (<i>Morus </i>spp.) and Related Species

“…All diploids mulberry species studied in this report are potential parents for crossbreeding. allopolyploids of several Triticeae species, nuclear DNA amounts are significantly smaller than the sum of their parental species (Eilam et al 2008(Eilam et al , 2009). Leitch & Bennett (2004) identified a tendency for 1Cx values of higher ploidy species to be smaller; however, in mulberry, the 1Cx values of three of four hexaploids were larger than those of diploids, although the 1Cx values of the docosaploid and a hexaploid were smaller and slightly smaller, respectively.…”

“…Thus, an increase in repetitive sequences may lead to an increase in genome size, whereas after polyploidization genome size can be rapidly reduced within one generation (Eilam et al 2008(Eilam et al , 2009). Both events may lead to changes in the 2C DNA value (the unreplicated genome DNA content).…”

Autotetraploid rice methylome analysis reveals methylation variation of transposable elements and their effects on gene expression

“…Biologists have long sought to understand how natural selection enabled neopolyploids to overcome early challenges. Many autopolyploidy systems have been developed for this purpose, such as Arabidopsis (11)(12)(13), potato (14), Elymus elongatus (15), Paspalum (16), and Cymbopogon (17). However, further investigations are still needed to examine the scope and scale of neopolyploids' responses to WGDs.…”