Phylogenomic placement of ancient polyploidy events within the Poales and Agavoideae (Asparagales)

Abstract

Polyploidy has been an important component to the evolution of angiosperms. Recent studies have shown that an ancient polyploid (paleopolyploid) event can be traced to the lineage leading to the diversification of all angiosperms, and it has long been known that recurring polyploid events can be found throughout the angiosperm tree of life. With the advent of high-throughput sequencing, the prominent place of paleopolyploid events in the evolutionary history of angiosperms has become increasingly clear. Polyploidy is thought to spur both diversification and trait innovation through the duplication and reworking of gene networks. Understanding the evolutionary impact of paleopolyploidy within the angiosperms requires knowing when these events occurred during angiosperm evolution. This study utilizes a high-throughput phylogenomic approach to identify the timing of paleopolyploid events by comparing the origin of paralogous genes within a gene family to a known species tree. Transcriptome data derived from taxa in lineages with previously little to no genomic data, were utilized to assess the timing of duplication events within hundreds of gene families. Previously described paleopolyploid events in the history of grasses, identified through analyses of syntenic blocks within Poaceae genomes, were placed on the Poales phylogeny and the implications of these events were considered. Additionally, a previously unverified paleopolyploidy event was found to have occurred in a common ancestor of all members of the Asparagales and commelinids (including Poales, Zingiberales, Commelinales, Arecales and Dasypogonales). The phylogeny of the Asparagaceae subfamily Agavoideae was resolved using whole chloroplast genomes, and two previously unknown paleopolyploid events were described within the context of that phylogeny. The potential effects of these paleopolyploid events on the evolution of the “Yucca-Agave” bimodal karyotype were discussed. This study demonstrates the utility of large transcriptomic sequencing projects and phylogenomic analyses of gene families to identify novel polyploid events and place them within an evolutionary context.