Abstract Detail

Recent Topics Posters

Charboneau, Joseph [1], Sanderson, Michael [1].

Did polyploidy predate the rapid radiation of New World Astragalus (Fabaceae)?

The advent of genomic sequence data has revealed polyploidy or whole-genome duplication (WGD) in plants is much more common than previously thought. While polyploidy previously had been known only in species with duplicated complements of chromosomes, it is now clear most vascular plants are paleopolyploids that have ancestors that underwent at least one round of WGD. In such cases, newly formed polyploids (neopolyploids) resulting from ancient WGDs underwent a process called diploidization, in which duplicated genes and chromosomal regions were lost or retained and the genome became reorganized into fewer chromosomes resulting in a functional diploid. Plant species that are still undergoing diploidization are called mesopolyploids and often have intermediate chromosome numbers greater than the diploid and less than the tetraploid numbers for the group. The New World clade of about 500 species in the genus Astragalus (Fabaceae) called Neo-Astragalus that originated only about 4.5 Mya displays such intermediate chromosome numbers in an aneuploid series with counts of n=11, 12, 13, 14, or 15. Because the most common Neo-Astragalus chromosome counts of n=11 and n=12 are nearly halfway between the diploid (n=8) and tetraploid (n=16) counts for the genus, it is unclear whether the aneuploid series in Neo-Astragalus is the result of a reduction in chromosome number from a polyploid ancestor or an increase from a diploid ancestor. To address this we sequenced and assembled transcriptomes of two Neo-Astragalus species. Using these transcriptomes and other previously sequenced legume transcriptomes including one from an Old World Astragalus species, we performed a phylogenomic analysis of gene duplications within groups of orthologous genes. We also completed an analysis of the distribution of the level of synonymous divergence (K_s) among duplicated gene pairs within Astragalus species. While the number of gene duplications mapped to the branch subtending Neo-Astragalus in the species tree is not obviously inflated, an overabundance of gene duplicates of approximately the same age shared by the two Neo-Astragalus species that is not found in the Old World Astragalus species indicates Neo-Astragalus has a polyploid ancestor not shared with Old World species. Neo-Astragalus species and other potential mesopolyploids in groups with chromosome number variation may help elucidate how diploidization has produced the many paleopolyploid plant species we see today.

1 - University of Arizona, Ecology and Evolutionary Biology, Tucson, AZ, 85721, USA

Keywords:
Polyploidy
WGD
diploidization
transcriptomics
Fabaceae.

Presentation Type: Recent Topics Poster
Session: P, Recent Topics Posters
Location: Grand Ballroom - Exhibit Hall/Mayo Civic Center
Date: Monday, July 23rd, 2018
Time: 5:30 PM
Number: PRT031
Abstract ID:1329
Candidate for Awards:None