Navigating the tip of the genomic iceberg: Next-generation sequencing for plant systematics.

TLDR: The utility of genome skimming is demonstrated through phylogenetic analysis of the Sonoran Desert clade (SDC) of Asclepias (Apocynaceae) and the effect of divergence on reference-guided plastome assembly is addressed.

Abstract:  Premise of the study: Just as Sanger sequencing did more than 20 years ago, next-generation sequencing (NGS) is poised to revolutionize plant systematics By combining multiplexing approaches with NGS throughput, systematists may no longer need to choose between more taxa or more characters Here we describe a genome skimming (shallow sequencing) approach for plant systematics  Methods: Through simulations, we evaluated optimal sequencing depth and performance of single-end and paired-end short read sequences for assembly of nuclear ribosomal DNA (rDNA) and plastomes and addressed the effect of divergence on reference-guided plastome assembly We also used simulations to identify potential phylogenetic markers from low-copy nuclear loci at different sequencing depths We demonstrated the utility of genome skimming through phylogenetic analysis of the Sonoran Desert clade (SDC) of Asclepias (Apocynaceae)  Key results: Paired-end reads performed better than single-end reads Minimum sequencing depths for high quality rDNA and plastome assemblies were 40 × and 30 × , respectively Divergence from the reference signifi cantly affected plastome assembly, but relatively similar references are available for most seed plants Deeper rDNA sequencing is necessary to characterize intragenomic polymorphism The low-copy fraction of the nuclear genome was readily surveyed, even at low sequencing depths Nearly 160 000 bp of sequence from three organelles provided evidence of phylogenetic incongruence in the SDC  Conclusions: Adoption of NGS will facilitate progress in plant systematics, as whole plastome and rDNA cistrons, partial mitochondrial genomes, and low-copy nuclear markers can now be effi ciently obtained for molecular phylogenetics studies