Tandem repeats on an eco-geographical scale: outcomes from the genome of Aegilops speltoides

Abstract

The chromosomal pattern of tandem repeat fractions of repetitive DNA is one of the most important characteristics of a species. In the present research, we aimed to detect and evaluate the level of intraspecific variability in the chromosomal distribution of species-specific Spelt 1 and Aegilops-Triticum-specific Spelt 52 tandem repeats in Aegilops speltoides and in closely related diploid and polyploid species. There is a distinct eco-geographical gradient in Spelt 1 and Spelt 52 blocks abundance in Ae. speltoides. In marginal populations, the number of Spelt 1 chromosomal blocks could be 12-14 times lower than in the center of the species distribution. Also, in related diploid species, the abundance of Spelt 52 correlates with evolutionary proximity to Ae. speltoides. Finally, the B- and G-genomes of allopolyploid wheats have Spelt 1 chromosomal distribution patterns similar to those of the types of Ae. speltoides with poor and rich contents of Spelt 1, respectively. The observed changes in numbers of blocks of Spelt 1 and Spelt 52 tandem repeats along the eco-geographical gradient may due to their depletion in the marginal populations as a result of increased recombination frequency under stressful conditions. Alternatively, it may be accumulation of tandem repeats in conducive climatic/edaphic environments in the center of the species' geographical distribution. Anyway, we observe a bidirectional shift of repetitive DNA genomic patterns on the population level leading to the formation of population-specific chromosomal patterns of tandem repeats. The appearance of a new chromosomal pattern is considered an important factor in promoting the emergence of interbreeding barriers.

Diversity of Long Terminal Repeat Retrotransposon Genome Distribution in Natural Populations of the Wild Diploid WheatAegilops speltoides

“…In both southern and northern marginal populations, we observed a significant decrease in the number of major blocks and detected repatterning. These results are similar to those obtained for species-specific tandem repeats in marginal populations (Raskina et al 2011). …”

“…It is likely that such an extreme environment has been a crucial factor in the changing pattern of the Daniela element. Although the mechanisms for this phenomenon are unclear, we speculate that it might have resulted from the high recombination rate that is typical of marginal populations (see also Raskina et al 2011); even so, it is possible that a transposition also contributed to the radical changes in the IRAP pattern.…”

“…It is likely that such an extreme environment has been a crucial factor in the changing pattern of the Daniela element. Although the mechanisms for this phenomenon are unclear, we speculate that it might have resulted from the high recombination rate that is typical of marginal populations (see also Raskina et al 2011); even so, it is possible that a transposition also contributed to the radical changes in the IRAP pattern.Further evidence of the permanence of LTR retrotransposon fraction repatterning was provided by time-line IRAP analysis of genotypes from the Technion 2 population, when three sets of plants collected in different years (T0, T2, and T5) were analyzed. This population is extremely small, degraded (i.e., partially destroyed by nearby construction and advancing shrubs), and isolated.…”

Genotype- and Cell-Specific Dynamics of Tandem Repeat Patterns in <b><i>Aegilops speltoides</i></b> Tausch (Poaceae, Triticeae)

“…al., 1996]. Limited numbers and distinct locations of the Spelt1 and Spelt52 clusters make these tandem repeats informative chromosomal markers and indicators of chromosomal rearrangements [Raskina et al, 2011]. The genome of Ae.…”

“…speltoides possesses a wide spectrum of chromosomal rearrangements and extranumerary B chromosomes [Mendelson and Zohary, 1972;Raskina et al, 2004aRaskina et al, , b, 2011 which are highly enriched with nuclear repetitive and organelle DNA [Ruban et al, 2014]. According to the chromosomal patterns of tandem repeats [Raskina et al, 2011] and inter-retrotransposon amplified polymorphism [Hosid et al, 2012], wild populations can be clustered into 3 groups, which reflect the Ae. speltoides ecogeographical gradient and highlight the impact of repetitive DNA on population divergence and evolutionarily significant events that lead to speciation at the diploid level and via allopolyploidy [Raskina et al, 2004a[Raskina et al, , b, 2008.…”