Genome Size in Diploids, Allopolyploids, and Autopolyploids of Mediterranean Triticeae

Abstract

Nuclear DNA amount, determined by the flow cytometry method, in diploids, natural and synthetic allopolyploids, and natural and synthetic autopolyploids of the tribe Triticeae (Poaceae) is reviewed here and discussed. In contrast to the very small and nonsignificant variation in nuclear DNA amount that was found at the intraspecific level, the variation at the interspecific level is very large. Evidently changes in genome size are either the cause or the result of speciation. Typical autopolyploids had the expected additive DNA amount of their diploid parents, whereas natural and synthetic cytologically diploidized autopolyploids and natural and synthetic allopolyploids had significantly less DNA than the sum of their parents. Thus, genome downsizing, occurring during or immediately after the formation of these polyploids, provides the physical basis for their cytological diploidization, that is, diploid-like meiotic behavior. Possible mechanisms that are involved in genome downsizing and the biological significance of this phenomenon are discussed.

Genome Evolution Due to Allopolyploidization in Wheat

“…exhibit a similar loss, indicating that DNA elimination occurs soon after allopolyploidization (Nishikawa and Furuta 1969;Furuta et al 1974;Eilam et al 2008Eilam et al , 2010. Also, the narrow intraspecific variation in DNA content of the allopolyploids supports that the loss of DNA occurred immediately after the allopolyploid formation and that there was almost no subsequent change in DNA content during the allopolyploid species evolution (Eilam et al 2008).…”

“…Most of the CSSs are noncoding sequences and are present in all the diploid species of Aegilops and Triticum, but occur in only one pair of chromosomes of allopolyploid wheat, suggesting that they were lost during or after allopolyploidization A most surprising discovery is that allopolyploidization in the wheat group causes immediate nonrandom elimination of specific noncoding, low-copy, and high-copy DNA sequences Liu et al 1998a,b;Ozkan et al 2001;Shaked et al 2001;Han et al 2003Han et al , 2005Salina et al 2004). The extent of DNA elimination was estimated by determining the amounts of nuclear DNA in natural allopolyploids and in their diploid progenitors, as well as in newly synthesized allopolyploids and their parental plants (Ozkan et al 2003;Eilam et al 2008Eilam et al , 2010. Natural wheat and related allopolyploids contain 2-10% less DNA than the sum of their diploid parents, and synthetic allopolyploids Figure 1 Schematic of the wheat karyotype.…”

“…In this synthetic allopolyploid, the various genomes were not affected equally: the wheat genomic sequences were relatively conserved, whereas the rye genomic sequences underwent a high level of variation and elimination (Ma et al 2004;Gustafson 2005, 2006). Similarly, in hexaploid wheat, genome D underwent a considerable reduction in DNA, while the A and B genomes were not reduced in size (Eilam et al 2008(Eilam et al , 2010. Bento et al (2011) reanalyzed data concerning genomic analysis of octoploid and hexaploid triticale and different synthetic wheat hybrids, in comparison with other polyploid species.…”

Can resource costs of polyploidy provide an advantage to sex?

“…This increased per-cell nuclear DNA content, however, does not necessarily translate into higher whole-organism P concentration. For one, polyploids often have larger (and fewer) cells (Fankhauser, 1945;Benfey, 1999;reviewed in Mable, 2004), and smaller haploid genomes (Ozkan et al, 2003;Leitch and Bennett, 2004;Murray et al, 2005;Gerstein et al, 2006;Eilam et al, 2010;Pellicer et al, 2010) relative to closely related taxa with lower ploidy. In addition, variation in RNA content may have more of an effect than variation in DNA content on body P content because RNA (1) makes up a substantial fraction of organismal biomass (415% dry mass in some animals and 440% dry mass in bacteria; Elser et al, 1996Elser et al, , 2003 and (2) varies considerably among taxa (for example, %RNA ranges from o1% to 413% dry mass in zooplankton (Gillooly et al, 2005)).…”

Retrotransposons Represent the Most Labile Fraction for Genomic Rearrangements in Polyploid Plant Species

“…Autopolyploids are classified into 2 main types: 'typical' autopolyploids, characterised by multivalent pairing at meiosis and multisomic inheritance, and 'cytologically diploidised' autopolyploids, which exhibit almost exclusively homologous pairing at meiosis, although they have more than 2 genome copies [Eilam et al, 2010]. Cytologically diploidised autotetraploids display considerable genome downsizing immediately after autopolyploidisation, such as in the synthetic autopolyploid Phlox drummondii, where reductions of up to ∼ 25% of the total parental DNA content in the third generation have been observed [Eilam et al, 2010].…”