Backbone phylogeny and evolution of Apioideae (Apiaceae): New insights from phylogenomic analyses of plastome data.

Traditional phylogenies inferred from chloroplast DNA fragments have not obtained a well-resolved evolutionary history for the backbone of Apioideae, the largest subfamily of Apiaceae. In this study, we applied the genome skimming approach of next-generation sequencing to address whether the lack of resolution at the tip of the Apioideae phylogenetic tree is due to limited information loci or the footprint of ancient radiation. A total of 90 complete chloroplast genomes (including 23 newly sequenced genomes and covering 20 major clades of Apioideae) were analyzed (RAxML and MrBayes) to provide a phylogenomic reconstruction of Apioideae. Dating analysis was also implemented using BEAST to estimate the origin and divergence time of the major clades. As a result, the early divergences of Apioideae have been clarified but the relationship among its distally branching clades (Group A) was only partially resolved, with short internal branches pointing to an ancient radiation scenario. Four major clades, Tordyliinae I, Pimpinelleae I, Apieae and Coriandreae, were hypothesized to have originated from chloroplast capture events induced by early hybridization according to the incongruence between chloroplast-based and nrDNA-based phylogenetic trees. Furthermore, the variable and nested distribution of junction positions of LSC (Large single copy region) and IRB (inverted repeat region B) in Group A may reflect incomplete lineage sorting within this group, which possibly contributed to the unclear phylogenetic relationships among these clades inferred from plastome data. Molecular clock analysis revealed the chloroplast capture events mainly occurred during the middle to late Miocene, providing a geological and climate context for the evolution of Apioideae.

Comparative Analysis of the Chloroplast Genomes of the Chinese Endemic Genus Urophysa and Their Contribution to Chloroplast Phylogeny and Adaptive Evolution.

Urophysa is a Chinese endemic genus comprising two species, Urophysa rockii and Urophysa henryi. In this study, we sequenced the complete chloroplast (cp) genomes of these two species and of their relative Semiquilegia adoxoides. Illumina sequencing technology was used to compare sequences, elucidate the intra- and interspecies variations, and infer the phylogeny relationship with other Ranunculaceae family species. A typical quadripartite structure was detected, with a genome size from 158,473 to 158,512 bp, consisting of a pair of inverted repeats separated by a small single-copy region and a large single-copy region. We analyzed the nucleotide diversity and repeated sequences components and conducted a positive selection analysis by the codon-based substitution on single-copy coding sequence (CDS). Seven regions were found to possess relatively high nucleotide diversity, and numerous variable repeats and simple sequence repeats (SSR) markers were detected. Six single-copy genes (atpA, rpl20, psaA, atpB, ndhI, and rbcL) resulted to have high posterior probabilities of codon sites in the positive selection analysis, which means that the six genes may be under a great selection pressure. The visualization results of the six genes showed that the amino acid properties across each column of all species are variable in different genera. All these regions with high nucleotide diversity, abundant repeats, and under positive selection will provide potential plastid markers for further taxonomic, phylogenetic, and population genetics studies in Urophysa and its relatives. Phylogenetic analyses based on the 79 single-copy genes, the whole complete genome sequences, and all CDS sequences showed same topologies with high support, and U. rockii was closely clustered with U. henryi within the Urophysa genus, with S. adoxoides as their closest relative. Therefore, the complete cp genomes in Urophysa species provide interesting insights and valuable information that can be used to identify related species and reconstruct their phylogeny.

The Chloroplast Genome of Lilium henrici: Genome Structure and Comparative Analysis.

Lilium henrici Franchet, which belongs to the family Liliaceae, is an endangered plant native to China. The wild populations of L. henrici have been largely reduced by habitat degradation or loss. In our study, we determined the whole chloroplast genome sequence for L. henrici and compared its structure with other Lilium (including Nomocharis) species. The chloroplast genome of L. henrici is a circular structure and 152,784 bp in length. The large single copy and small single copy is 82,429 bp and 17,533 bp in size, respectively, and the inverted repeats are 26,411 bp in size. The L. henrici chloroplast genome contains 116 different genes, including 78 protein coding genes, 30 tRNA genes, 4 rRNA genes, and 4 pseudogenes. There were 51 SSRs detected in the L. henrici chloroplast genome sequence. Genic comparison among L. henrici with other Lilium (including Nomocharis) chloroplast genomes shows that the sequence lengths and gene contents show little variation, the only differences being in three pseudogenes. Phylogenetic analysis revealed that N. pardanthina was a sister species to L. henrici. Overall, this study, providing L. henrici genomic resources and the comparative analysis of Lilium chloroplast genomes, will be beneficial for the evolutionary study and phylogenetic reconstruction of the genus Lilium, molecular barcoding in population genetics.

Phylogeny of Chinese Allium Species in Section Daghestanica and Adaptive Evolution of Allium (Amaryllidaceae, Allioideae) Species Revealed by the Chloroplast Complete Genome.

The genus Allium (Amaryllidaceae, Allioideae) is one of the largest monocotyledonous genera and it includes many economically important crops that are cultivated for consumption or medicinal uses. Recent advances in molecular phylogenetics have revolutionized our understanding of Allium taxonomy and evolution. However, the phylogenetic relationships in some Allium sections (such as the Allium section Daghestanica) and the genetic bases of adaptative evolution, remain poorly understood. Here, we newly assembled six chloroplast genomes from Chinese endemic species in Allium section Daghestanica and by combining these genomes with another 35 allied species, we performed a series of analyses including genome structure, GC content, species pairwise Ka/Ks ratios, and the SSR component, nucleotide diversity and codon usage. Positively selected genes (PSGs) were detected in the Allium lineage using the branch-site model. Comparison analysis of Bayesian and ML phylogeny on CCG (complete chloroplast genome), SCG (single copy genes) and CDS (coding DNA sequences) produced a well-resolved phylogeny of Allioideae plastid lineages, which illustrated several novel relationships with the section Daghestanica. In addition, six species in section Daghestanica showed highly conserved structures. The GC content and the GC3s content in Allioideae species exhibited lower values than studied non-Allioideae species, along with elevated pairwise Ka/Ks ratios. The rps2 gene was lost in all examined Allioideae species, and 10 genes with significant posterior probabilities for codon sites were identified in the positive selection analysis, seven of them are associated with photosynthesis. Our study uncovered a new species relationship in section Daghestanica and suggested that the selective pressure has played an important role in Allium adaptation and evolution, these results will facilitate our further understanding of evolution and adaptation of species in the genus Allium.

The complete chloroplast genome of Angelica nitida.

Angelica nitida is an endemic species in China. The complete chloroplast genome sequence of A. nitida was generated by de novo assembly using whole genome next generation sequencing. The complete chloroplast genome was 146,512bp in length and constructed out of four parts - a large single copy (LSC) region of 93,298bp, a small single copy (SSC) region of 18,068bp and two inverted repeat (IRa and IRb) regions of 17,573bp each. The genome annotation predicted a total of 113 genes, including 80 protein-coding genes, 29 tRNA genes, and 4 rRNA genes. Phylogenetic analysis with the reported chloroplast genomes revealed that A. nitida is most closely related to Angelica dahurica.