Genome size dynamics in Artemisia L. (Asteraceae): following the track of polyploidy

Abstract

Polyploidy is a key factor in the evolution of higher plants and plays an important role in the variation of plant genomes, leading to speciation in some cases. During polyploidisation, different balancing processes take place at the genomic level that can promote variation in nuclear DNA content. We estimated genome size using flow cytometry in 84 populations of 67 Artemisia species and one population of Crossostephium chinense. A total of 73 sequences of nrDNA ITS and 3'-ETS were newly generated and analysed, together with previously published sequences, to address the evolution of genome size in a phylogenetic framework. Differences in 2C values were detected among some lineages, as well as an increase of genome size heterogeneity in subgenera whose phylogenetic relationships are still unclear. We confirmed that the increase in 2C values in Artemisia polyploids was not proportional to ploidy level, but 1Cx genome size tended to decrease significantly when high ploidy levels were reached. The results lead us to hypothesise that genome size in polyploids tends to a maximum as it follows saturation behaviour, in agreement with the Michaelis-Menten model. We tested different arithmetic functions with our dataset that corroborated a non-linear relationship of genome size increase in polyploids, allowing us to suggest a theoretical upper limit for the DNA content of this genus.

Genome size variation in the genus Avena

“…The hypothesis that the B genome is smaller than the A genome was put forward by Iiyama and Grant (1972) for this reason, although this was also in support of a proposed AABBDD genome constitution for the hexaploid, which has been subsequently rejected. Polyploid genome downsizing has been observed in most angiosperms, and it is assumed to be a general trend (Kellogg and Bennetzen 2004;Pellicer et al 2010a). The mechanisms leading to loss of the DNA in polyploids include unequal homologous recombination (Bennetzen et al 2005), non-homologous recombination (Devos et al 2002), general elimination of redundant DNA (Ozkan et al 2003;Leitch and Bennett 2004), and specific elimination of duplicate genes (Renny-Byfield and Wendel 2014; Evans et al 2015).…”

“…However, genome size can vary over several orders of magnitude in eukaryotes (Bennett and Leitch 2005;Pellicer et al 2010a). In Angiosperms, 2C values range from 0.13 pg in Genlisea aurea (Greilhuber et al 2006) to 304.4 pg in Paris japonica (Pellicer et al 2010b).…”

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)).…”

Life cycle versus systematic placement: phylogenetic and cytogenetic studies in annual Artemisia (Asteraceae, Anthemideae)

“…Samples were subsequently stained with PI to a final concentration of 60 µg/mL (Sigma-Aldrich Química), kept on ice for 20 min, and measured in an Epics XL flow cytometer (Coulter Corporation). Further technical details regarding the procedure can be found in Pellicer et al (2010b). Measurements were carried out at the Scientific and Technological Centers, University of Barcelona.…”

“…The distribution pattern of annual species confirmed that these taxa were concentrated in the earlier branches of the tree, whilst the core of the subgenera Artemisia, Pacifica, Seriphidium, and Tridentatae, which are late-branched, completely lacked annual representatives (Figure 1 . annua, A. leucodes, A. magellanica, A. scoparia, and A. tournefortiana (Torrell and Vallès, 2001;Garcia et al, 2004;Pellicer et al, 2010b). Genome sizes varied ca.…”