Ancient Polyploidy and Genome Evolution in Palms

Mechanisms of genome evolution are fundamental to our understanding of adaptation and the generation and maintenance of biodiversity, yet genome dynamics are still poorly characterized in many clades. Strong correlations between variation in genomic attributes and species diversity across the plant tree of life suggest that polyploidy or other mechanisms of genome size change confer selective advantages due to the introduction of genomic novelty. Palms (order Arecales, family Arecaceae) are diverse, widespread, and dominant in tropical ecosystems, yet little is known about genome evolution in this ecologically and economically important clade. Here, we take a phylogenetic comparative approach to investigate palm genome dynamics using genomic and transcriptomic data in combination with a recent, densely sampled, phylogenetic tree. We find conclusive evidence of a paleopolyploid event shared by the ancestor of palms but not with the sister clade, Dasypogonales. We find evidence of incremental chromosome number change in the palms as opposed to one of recurrent polyploidy. We find strong phylogenetic signal in chromosome number, but no signal in genome size, and further no correlation between the two when correcting for phylogenetic relationships. Palms thus add to a growing number of diverse, ecologically successful clades with evidence of whole-genome duplication, sister to a species-poor clade with no evidence of such an event. Disentangling the causes of genome size variation in palms moves us closer to understanding the genomic conditions facilitating adaptive radiation and ecological dominance in an evolutionarily successful, emblematic tropical clade

Complete plastid genome of the Chinese medicinal herb Paeonia obovata subsp. Willmottiae (Paeoniaceae): characterization and phylogeny

The plastid genome (plastome) of the endemic Chinese medicinal herb Paeonia obovata subsp. Willmottiae (Paeoniaceae) was sequenced and investigated in this study. The complete plastome is 152,713 bp in length with the typical quadripartite structure, which consists of a large single-copy region (LSC, 84,419 bp), a small single-copy region (SSC, 16,982 bp), and a pair of inverted repeat regions (IRs, 25,656 bp). The overall GC content is 33.2%, and the IR regions are more GC rich (43.2%) than the LSC (36.7%) and SSC (32.8%) regions. A total of 114 unique genes, including 79 protein-coding genes, 31 tRNAs, and four rRNAs were identified. Phylogenetic reconstruction based on complete plastome sequences demonstrated that P. obovata subsp. Willmottiae is phylogenetically closest to P. obovata

Genetic variation in Rheum palmatum and Rheum tanguticum (Polygonaceae), two medicinally and endemic species in China using ISSR markers.

AIMS: Both Rheum palmatum and R. tanguticum are important but endangered medicinal plants endemic to China. In this study, we aimed to (i) investigate the level and pattern of genetic variability within/among populations of those species; (ii) evaluate genetic differentiation between both species and its relationships and ascertain whether both species are consistent with their current taxonomical treatment as separate species; and (iii) discuss the implications for the effective conservation of two species. METHODS: Total 574 individuals from 30 populations of R. palmatum and R. tanguticum were collected, covering the entire distribution range of two species in China. The genetic variation within and among 30 populations was evaluated using inter-simple sequence repeat (ISSR) markers. IMPORTANT FINDINGS: Twelve selected ISSR primers generated a total of 175 fragments, 173 (98.86%) of which were polymorphic. The Nei's gene diversity (H) and Shannon's index (I) of both species were high at species level (H = 0.3107, I = 0.4677 for R. palmatum; H = 0.2848, I = 0.4333 for R. tanguticum). But for both species, the genetic diversity was low at population level, and average within-population diversity of R. palmatum was H = 0.1438, I = 0.2151, and that of R. tanguticum was H = 0.1415, I = 0.2126. The hierarchical AMOVA revealed high levels of among-population genetic differentiation in both species, in line with the gene differentiation coefficient and the limited among-population gene flow (R. palmatum: Φ(st) = 0.592, G(st) = 0.537, N(m) = 0.432; R. tanguticum: Φ(st) = 0.567, G(st) = 0.497, N(m) = 0.507). By contrast, only 6.52% of the total genetic variance was partitioned between R. palmatum and R. tanguticum. Bayesian analysis, UPGMA cluster analysis, and PCoA analysis all demonstrated the similar results. A significant isolation-by-distance pattern was revealed in R. palmatum (r = 0.547, P = 0.010), but not in R. tanguticum (r = 0.241, P = 0.100). Based on these results, effective conservation strategies were proposed for these two species. The small molecular variance between R. palmatum and R. tanguticum revealed that they had a common ancestor, and we considered that these two species might not be good species

Analysis of chloroplast genome characteristics of three medicinal plants of Panax in Qinba Mountains

In order to clarify the phylogenetic relationship between the chloroplast genome characteristics of three medicinal plants, Panax japonicus var. major, P. japonicus var. bipinnatifidus, P. pseudoginseng var. elegantior in Qinba Mountains, we analysed the chloroplast genome characteristics and codon usage preferences by using bioinformatics techniques. The results were as follows: (1) The chloroplast genomes of three species of Panax were typical tetrad structure, the genome full size was between 156 071 to 156 104 bp, and the total GC-content was 38.10% with a high degree of genome size similarity. (2) A total of 133 coding genes were annotated, including 88 protein coding genes (PCGs), 37 tRNA genes, and 8 rRNA genes with a high degree of genome size similarity. (3) The chloroplast codon usage preferences of the three medicinal plants were comparable, with the third base of codon predominantly ending in A/U. Despite being affected by mutations, the codon usage patterns of the three medicinal plants were found to be mainly influenced by natural selection. (4) The phylogenetic results showed that the three Panax species were closely related, and P. pseudoginseng var. elegantior was more closely related to P. japonicus var. bipinnatifidus. In conclusion, this study presents a significant relationship between P. pseudoginseng var. elegantior and the original pharmacopeial plants of P. japonicus var. major. This finding has great importance for the development, utilization, and molecular identification of traditional Chinese medicinal material resources from P. japonicus var. major, and provides an important basis for further studies on the classification, phylogeny and evolutionary mechanisms of Panax species

Metabolome and transcriptome analyses identify the characteristics and expression of related saponins of the three genealogical plants of bead ginseng

Objective The classification and clinical usage of the different species of bead ginseng are often confused. Therefore, we conducted an integrated metabolomics and transcriptome analysis of three main species of Panax, including Panax japonicas, Panax pseudoginseng, and Panax pseudo-ginseng var. elegantior. Methods A broad metabolome and transcriptome analysis for three origins of bead ginseng plants was performed using UPLC-ESI-MS/MS, RNA sequencing and annotation, and bioinformatic analysis of transcriptome data. Results The levels of 830 metabolites were determined. A total of 291 differentially accumulated metabolites (DAMs) between Panax pseudo-ginseng var. elegantior and Panax japonicas (Group A), with 73 upregulated and 218 downregulated. A total of 331 DAMs (110 upregulated and 221 downregulated) were found between Panax pseudoginseng and Panax japonicas (group B). There were 160 DAMs (102 up-regulated and 58 down-regulated) between Panax pseudoginseng and Panax pseudo-ginseng var. elegantior (group C). In addition, RNA sequencing was performed in the above three ways. A total of 16,074 differential expression genes (DEGs) were detected between Group A, in which 7,723 genes were upregulated and 8,351 genes were downregulated by RNA sequencing. Similarly, 15,705 genes were differentially expressed between group B, in which 7,436 genes were upregulated and 8,269 genes were downregulated. However, only 1,294 genes were differentially expressed between group C, in which 531 genes were upregulated and 763 genes were downregulated. We performed differential gene analysis on three groups of samples according to the Venn diagram and found that 181 differential genes were present. A total of 3,698 and 2,834 unique genes were in groups A and B, while 130 unique genes were in group C. Conclusions This study provides metabolome and transcriptome information for three bead ginseng plants. The analysis of the metabolite content showed differences in the attributes of the three bead ginseng, contained mainly flavonoids, phenolic acids as well as terpenes

Ancient Polyploidy and Genome Evolution in Palms

Mechanisms of genome evolution are fundamental to our understanding of adaptation and the generation and maintenance of biodiversity, yet genome dynamics are still poorly characterized in many clades. Strong correlations between variation in genomic attributes and species diversity across the plant tree of life suggest that polyploidy or other mechanisms of genome size change confer selective advantages due to the introduction of genomic novelty. Palms (order Arecales, family Arecaceae) are diverse, widespread, and dominant in tropical ecosystems, yet little is known about genome evolution in this ecologically and economically important clade. Here, we take a phylogenetic comparative approach to investigate palm genome dynamics using genomic and transcriptomic data in combination with a recent, densely sampled, phylogenetic tree. We find conclusive evidence of a paleopolyploid event shared by the ancestor of palms but not with the sister clade, Dasypogonales. We find evidence of incremental chromosome number change in the palms as opposed to one of recurrent polyploidy. We find strong phylogenetic signal in chromosome number, but no signal in genome size, and further no correlation between the two when correcting for phylogenetic relationships. Palms thus add to a growing number of diverse, ecologically successful clades with evidence of whole-genome duplication, sister to a species-poor clade with no evidence of such an event. Disentangling the causes of genome size variation in palms moves us closer to understanding the genomic conditions facilitating adaptive radiation and ecological dominance in an evolutionarily successful, emblematic tropical clade

Geographic distribution of the 30 studied populations of <i>R. palmatum</i> and <i>R. tanguticum</i> in China.

<p>For population codes, see <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0051667#pone-0051667-t001" target="_blank">Table 1</a>.</p

Sampling details of the populations of <i>R. palmatum</i> (21) and <i>R. tanguticum</i> (9) in the present study.

<p>Sampling details of the populations of <i>R. palmatum</i> (21) and <i>R. tanguticum</i> (9) in the present study.</p

Results of the Bayesian assignment analysis using the program STRUCTURE.

<p>The <i>ΔK</i> (Evanno et al. 2005) was plotted against various values of <i>K</i>, suggesting <i>K</i> = 2 as the most likely number of clusters.</p