Entire plastid phylogeny of the carrot genus (Daucus, Apiaceae): Concordance with nuclear data and mitochondrial and nuclear DNA insertions to the plastid

Abstract

Premise of the study: We explored the phylogenetic utility of entire plastid DNA sequences in Daucus and compared the results with prior phylogenetic results using plastid and nuclear DNA sequences.

Methods: We used Illumina sequencing to obtain full plastid sequences of 37 accessions of 20 Daucus taxa and outgroups, analyzed the data with phylogenetic methods, and examined evidence for mitochondrial DNA transfer to the plastid (DcMP).

Key results: Our phylogenetic trees of the entire data set were highly resolved, with 100% bootstrap support for most of the external and many of the internal clades, except for the clade of D. carota and its most closely related species D. syrticus. Subsets of the data, including regions traditionally used as phylogenetically informative regions, provide various degrees of soft congruence with the entire data set. There are areas of hard incongruence, however, with phylogenies using nuclear data. We extended knowledge of a mitochondrial to plastid DNA insertion sequence previously named DcMP and identified the first instance in flowering plants of a sequence of potential nuclear genome origin inserted into the plastid genome. There is a relationship of inverted repeat junction classes and repeat DNA to phylogeny, but no such relationship with nonsynonymous mutations.

Conclusions: Our data have allowed us to (1) produce a well-resolved plastid phylogeny of Daucus, (2) evaluate subsets of the entire plastid data for phylogeny, (3) examine evidence for plastid and nuclear DNA phylogenetic incongruence, and (4) examine mitochondrial and nuclear DNA insertion into the plastid.

Keywords: Apiaceae; Daucus; DcMP; carrot; germplasm; mitochondria; next-generation sequencing; nuclear-to-plastid DNA transfer; plastid phylogeny.