Most Compositae (Asteraceae) are descendants of a paleohexaploid and all share a paleotetraploid ancestor with the Calyceraceae

Abstract

Our analyses of new samples with new tools provide a revised view of paleopolyploidy in the Compositae. Together with results from a high density Lactuca linkage map, our results suggest that the Compositae and Calyceraceae have a common paleotetraploid ancestor and that most Compositae are descendants of a paleohexaploid. Although paleohexaploids have been previously identified, this is the first example where the paleotetraploid and paleohexaploid lineages have survived over tens of millions of years. The complex polyploidy in the ancestry of the Compositae and Calyceraceae represents a unique opportunity to study the long-term evolutionary fates and consequences of different ploidal levels.

The Evolution of Haploid Chromosome Numbers in the Sunflower Family

“…Inside each circle (at interior nodes) the ancestral chromosome number with the highest probability is given. The differences observed between our study and previous ones (Barker et al 2008, 2016) are highlighted as red and orange branches, respectively. Overall, our approach did not infer any paleoploidization events near the base of the family, nor any paleoploidization shared with the sister family, Calyceraceae.…”

“…In particular, a paleopolyploidization event near the origin of the family, just prior to the rapid radiation of its tribes, as recently suggested (Barker et al. 2008, 2016) to be shared with Calyceraceae (the sister family of Asteraceae) was not observed in our case. Also, a paleohexaploidization event in the ancestry of the core of Asteraceae (except Barnadesia ) (Barker et al.…”

“…2002; Barker et al. 2008, 2016). Nevertheless, according to our results, a paleopolyploidization event seems to have occurred at the base of the Heliantheae tribe sensu stricto (s.s.), instead of having occurred at the base of the Heliantheae alliance, that is, Heliantheae sensu lato (s.l.…”

The sunflower genome provides insights into oil metabolism, flowering and Asterid evolution

“…We identified orthologous genes between the sunflower and grape-coffeelettuce-artichoke as well as paralogous genes within the sunflower (Supplementary Data 2 and Supplementary Note 3.1), coffee and artichoke genomes. In addition to WGT-γ (common with grape, artichoke, lettuce, coffee and sunflower) we established that sunflower, lettuce and artichoke experienced a whole-genome triplication (WGT-1) 15,16 , which has recently been proposed as independent genome duplications that are close in time 6 . A minimum of 3 chromosomal fissions and 57 chromosomal fusions were necessary for the lettuce to reach its current structure of 9 chromosomes, and 14 fissions and 60 fusions for the artichoke to reach 17 modern chromosomes.…”

“…The genome mostly consists of highly similar, related sequences 5 and required single-molecule realtime sequencing technologies for successful assembly. Genome analyses enabled the reconstruction of the evolutionary history of the Asterids, further establishing the existence of a whole-genome triplication at the base of the Asterids II clade 6 and a sunflowerspecific whole-genome duplication around 29 million years ago 7 . An integrative approach combining quantitative genetics, expression and diversity data permitted development of comprehensive gene networks for two major breeding traits, flowering time and oil metabolism, and revealed new candidate genes in these networks.…”