Genome size and genome evolution in diploid Triticeae species

Abstract

One of the intriguing issues concerning the dynamics of plant genomes is the occurrence of intraspecific variation in nuclear DNA amount. The aim of this work was to assess the ranges of intraspecific, interspecific, and intergeneric variation in nuclear DNA content of diploid species of the tribe Triticeae (Poaceae) and to examine the relation between life form or habitat and genome size. Altogether, 438 plants representing 272 lines that belong to 22 species were analyzed. Nuclear DNA content was estimated by flow cytometry. Very small intraspecific variation in DNA amount was found between lines of Triticeae diploid species collected from different habitats or between different morphs. In contrast to the constancy in nuclear DNA amount at the intraspecific level, there are significant differences in genome size between the various diploid species. Within the genus Aegilops, the 1C DNA amount ranged from 4.84 pg in A. caudata to 7.52 pg in A. sharonensis; among genera, the 1C DNA amount ranged from 4.18 pg in Heteranthelium piliferum to 9.45 pg in Secale montanum. No evidence was found for a smaller genome size in annual, self-pollinating species relative to perennial, cross-pollinating ones. Diploids that grow in the southern part of the group's distribution have larger genomes than those growing in other parts of the distribution. The contrast between the low variation at the intraspecific level and the high variation at the interspecific one suggests that changes in genome size originated in close temporal proximity to the speciation event, i.e., before, during, or immediately after it. The possible effects of sudden changes in genome size on speciation processes are discussed.

Genome size variation in the genus Avena

“…The existence of intraspecific variation in genome size is controversial. Although numerous studies have reported intraspecific variation (Schmuths et al 2004;Wang et al 2009;Díez et al 2013), it is more common to find stability within species (Lysák et al 2000;Greilhuber et al 2005;Eilam et al 2007), and some perceived intraspecific variation may be explained by other factors such as endogenous staining inhibitors or other methodical noise (Greilhuber 2005;Noirot et al 2005;Loureiro et al 2006). Thus, our results are consistent with the concept of intra-species stability in genome size.…”

“…The 2C values of species with identical genomic constitutions were generally continuous with only minor differences. This suggests that there have been no major events driving divergence within a genome type, and this is consistent with observations in the related genera Triticeae (Eilam et al 2007). Small but significant variations were detected, even among closely related diploids with identical sub-genome designations by the LSD test.…”

“…1) with CV n of the G0/G1 peaks ranging from 1.14% to 3.80% (mean 2.14%). The average CV t among technical replications on separate days was 1.25%, which was lower than previous reported variation (1.53%) in diploid species of Triticeae (Eilam et al 2007). The mean 2C values of individual accessions varied 3.1-fold, ranging from 8.41 to 26.24 pg.…”

Cloning and Characterization of TaTGW-7A Gene Associated with Grain Weight in Wheat via SLAF-seq-BSA

“…Moreover, wheat genome contains a high proportion (>80%) of repeated sequences (Eilam et al, 2007; Wicker et al, 2011), making map-based cloning difficult and time consuming. The SLAF-seq for marker development is highly efficient, inexpensive, and applicable for analyses of large populations; hence, it has been proposed as an effective method for marker-assisted breeding (Sun et al, 2013).…”

Characterisation and Analysis of the Aegilops sharonensis Transcriptome, a Wild Relative of Wheat in the Sitopsis Section

“…sharonensis is estimated at 7.5 Gb [23,24] and is expected to be largely made up of repeat elements. Therefore, sequencing the gene space is likely to represent a several hundred-fold reduction in complexity.…”