Phylogenetic trends and environmental correlates of nuclear genome size variation in Helianthus sunflowers

Abstract

Flowering plants serve as a powerful model for studying the evolution of nuclear genome size (GS) given the tremendous GS variation that exists both within and across angiosperm lineages.Helianthus sunflowers consist of c. 50 species native to North America that occupy diverse habitats and vary in ploidy level. In the current study, we generated a comprehensive GS database for 49 Helianthus species using flow cytometric approaches. We examined variability across the genus and present a comparative phylogenetic analysis of GS evolution in diploid Helianthus species.Results demonstrated that different clades of diploid Helianthus species showed evolutionary patterns of GS contraction, expansion and relative stasis, with annual diploid species evolving smaller GS with the highest rate of evolution. Phylogenetic comparative analyses of diploids revealed significant negative associations of GS with temperature seasonality and cell production rate, indicating that the evolution of larger GS in Helianthus diploids may be more permissible in habitats with longer growing seasons where selection for more rapid growth may be relaxed.The Helianthus GS database presented here and corresponding analyses of environmental and phenotypic correlates will facilitate ongoing and future research on the ultimate drivers of GS evolution in this well-studied North American plant genus.

Massive haplotypes underlie ecotypic differentiation in sunflowers

“…Are other haploblocks also involved in local adaptation? Theory suggests that SVs are likely to establish by capturing multiple adaptive alleles 39 ; consistent with this, when we treated haploblocks as individual loci, we found that haploblocks are often associated with multiple types of traits ( 8,9). Surprisingly, some of the strongest association we identified with this approach did not show up in our initial GWA and GEA analyses.…”

Intraspecific genetic divergence within Helianthus niveus and the status of two new morphotypes from Mexico

“…tephrodes. Variability in genome size of this magnitude is more typical of that previously reported between rather than within other sunflower species (Sims and Price, 1985;Jan, 2006;Qiu et al, 2019). In addition, subsp.…”

“…The larger genome sizes observed in these ecotypes and subsp. niveus are likely a result of the lower temperature seasonality of Baja California, which permits slower growth and lower cell production rate; consequently, selection for genome contraction may be relaxed (Qiu et al, 2019). It is also possible that smaller populations tend to respond more to drift and less to selection and thus have the potential to accumulate more transposable elements.…”

Gene banks for wild and cultivated sunflower genetic resources

“…They are highly heterozygous, and it is more difficult to obtain the two haplotypes of the chromosomes for the diploid species. Some wild relatives have more complex ploidy and can be larger, up to 11.21Gb in H. agrestis (Qiu et al, 2018).…”