Evolutionary roles of polyploidization-derived structural variations in the phenotypic diversification of Panax species.

Genomic structural variations (SVs) are widespread in plant and animal genomes and play important roles in phenotypic novelty and species adaptation. Frequent whole genome duplications followed by (re)diploidizations have resulted in high diversity of genome architecture among extant species. In this study, we identified abundant genomic SVs in the Panax genus that are hypothesized to have occurred through during the repeated polyploidizations/(re)diploidizations. Our genome-wide comparisons demonstrated that although these polyploidization-derived SVs have evolved at distinct evolutionary stages, a large number of SV-intersecting genes showed enrichment in functionally important pathways related to secondary metabolites, photosynthesis and basic cellular activities. In line with these observations, our metabolic analyses of these Panax species revealed high diversity of primary and secondary metabolites both at the tissue and interspecific levels. In particular, genomic SVs identified at ginsenoside biosynthesis genes, including copy number variation and large fragment deletion, appear to have played important roles in the evolution and diversification of ginsenosides. A further herbivore deterrence experiment demonstrated that, as major triterpenoidal saponins found exclusively in Panax, ginsenosides provide protection against insect herbivores. Our study provides new insights on how polyploidization-derived SVs have contributed to phenotypic novelty and plant adaptation.

Phenotypic and transcriptomic responses of the shade-grown species Panax ginseng to variable light conditions.

BACKGROUND AND AIMS: Elucidating how plant species respond to variable light conditions is important to understand the ecological adaptation to heterogeneous natural habitats. Plant performance and its underlying gene regulatory network have been well documented in sun-grown plants. However, the phenotypic and molecular responses of shade-grown plants under variable light conditions have remained largely unclear. METHODS: We assessed the differences in phenotypic performance between Panax ginseng (shade-grown) and Arabidopsis thaliana (sun-grown) under sunlight, shade and deep-shade conditions. To further address the molecular bases underpinning the phenotypic responses, we compared time-course transcriptomic expression profiling and candidate gene structures between the two species. KEY RESULTS: Our results show that, compared with arabidopsis, ginseng plants not only possess a lower degree of phenotypic plasticity among the three light conditions, but also exhibit higher photosynthetic efficiency under shade and deep-shade conditions. Further comparisons of the gene expression and structure reveal that differential transcriptional regulation together with increased copy number of photosynthesis-related genes (e.g. electron transfer and carbon fixation) may improve the photosynthetic efficiency of ginseng plants under the two shade conditions. In contrast, the inactivation of phytochrome-interacting factors (i.e. absent and no upregulation of the PIF genes) are potentially associated with the observed low degree of phenotypic plasticity of ginseng plants under variable light conditions. CONCLUSIONS: Our study provides new insights into how shade-grown plants respond to variable light conditions. Candidate genes related to shade adaptation in ginseng provide valuable genetic resources for future molecular breeding of high-density planting crops.

Reshuffling of the ancestral core-eudicot genome shaped chromatin topology and epigenetic modification in Panax.

All extant core-eudicot plants share a common ancestral genome that has experienced cyclic polyploidizations and (re)diploidizations. Reshuffling of the ancestral core-eudicot genome generates abundant genomic diversity, but the role of this diversity in shaping the hierarchical genome architecture, such as chromatin topology and gene expression, remains poorly understood. Here, we assemble chromosome-level genomes of one diploid and three tetraploid Panax species and conduct in-depth comparative genomic and epigenomic analyses. We show that chromosomal interactions within each duplicated ancestral chromosome largely maintain in extant Panax species, albeit experiencing ca. 100-150 million years of evolution from a shared ancestor. Biased genetic fractionation and epigenetic regulation divergence during polyploidization/(re)diploidization processes generate remarkable biochemical diversity of secondary metabolites in the Panax genus. Our study provides a paleo-polyploidization perspective of how reshuffling of the ancestral core-eudicot genome leads to a highly dynamic genome and to the metabolic diversification of extant eudicot plants.

Evolutionary Contribution of Duplicated Genes to Genome Evolution in the Ginseng Species Complex.

Genes duplicated by whole genome duplication (WGD) and small-scale duplication (SSD) have played important roles in adaptive evolution of all flowering plants. However, it still remains underinvestigated how the distinct models of duplication events and their contending evolutionary patterns have shaped the genome and epigenomes of extant plant species. In this study, we investigated the contribution of the WGD- and SSD-derived duplicate genes to the genome evolution of one diploid and three closely related allotetraploid Panax species based on genome, methylome, and proteome data sets. Our genome-wide comparative analyses revealed that although the ginseng species complex was recently diverged, they have evolved distinct overall patterns of nucleotide variation, cytosine methylation, and protein-level expression. In particular, genetic and epigenetic asymmetries observed in the recent WGD-derived genes are largely consistent across the ginseng species complex. In addition, our results revealed that gene duplicates generated by ancient WGD and SSD mechanisms exhibited distinct evolutionary patterns. We found the ancient WGD-derived genes (i.e., ancient collinear gene) are genetically more conserved and hypomethylated at the cytosine sites. In contrast, some of the SSD-derived genes (i.e., dispersal duplicated gene) showed hypermethylation and high variance in nucleotide variation pattern. Functional enrichment analyses of the duplicated genes indicated that adaptation-related traits (i.e., photosynthesis) created during the distant ancient WGDs are further strengthened by both the more recent WGD and SSD. Together, our findings suggest that different types of duplicated genes may have played distinct but relaying evolutionary roles in the polyploidization and speciation processes in the ginseng species complex.

Efficacy of Long-term Selenium Supplementation in the Treatment of Chronic Keshan Disease with Congestive Heart Failure.

Few effective treatments for chronic Keshan disease have been available till now. The efficacy of long-term selenium supplementation in the treatment of chronic Keshan disease with congestive heart failure is inconclusive. This study aimed to determine whether selenium supplementation is associated with a decreased risk of cardiac death in chronic Keshan disease with congestive heart failure by ten years of follow-up. A retrospective long-term follow-up analysis was performed on a monitored cohort consisting of 302 chronic Keshan disease patients with a mean age of 40.8±11.4 years. Of the 302 chronic Keshan disease patients, 170 (56.3%) were given selenium supplementation until the end point of follow-up. Cox proportional hazards regression models were used to identify the independent predictors of cardiac events. Our results showed that during the follow-up, there were 101 deaths of patients with chronic Keshan disease in the selenium supplementation group (101/170, 59.4%) and 98 in non-selenium supplementation group (98/132, 74.2%). Multivariate analyses suggested that selenium supplementation was associated with a decreased risk of cardiac death (HR 0.39, 95% CI 0.28-0.53) after adjustment for baseline age, sex, cigarette smoking, family history of Keshan disease, body mass index (BMI), heart rate, electrocardiogram (ECG) abnormalities, blood pressure, initial cardiothoracic ratio, left ventricular ejection fractions (LVEF) and whole-blood selenium concentration. Our ten-year follow-up analysis indicated that selenium supplementation, specifically combined with the use of angiotensin-converting enzyme inhibitor and beta blocker therapy, improved the survival of patients with chronic Keshan disease with congestive heart failure. BMI, selenium deficiency, male, combined ECG abnormalities, LVEF, and fast heart rate increased the risk of cardiac events.

Genetic and Epigenetic Diversities Shed Light on Domestication of Cultivated Ginseng (Panax ginseng).

Chinese ginseng (Panax ginseng) is a medically important herb within Panax and has crucial cultural values in East Asia. As the symbol of traditional Chinese medicine, Chinese ginseng has been used as a herbal remedy to restore stamina and capacity in East Asia for thousands of years. To address the evolutionary origin and domestication history of cultivated ginseng, we employed multiple molecular approaches to investigate the genetic structures of cultivated and wild ginseng across their distribution ranges in northeastern Asia. Phylogenetic and population genetic analyses revealed that the four cultivated ginseng landraces, COMMON, BIANTIAO, SHIZHU, and GAOLI (also known as Korean ginseng), were not domesticated independently and Fusong Town is likely one of the primary domestication centers. In addition, our results from population genetic and epigenetic analyses demonstrated that cultivated ginseng maintained high levels of genetic and epigenetic diversity, but showed distinct cytosine methylation patterns compared with wild ginseng. The patterns of genetic and epigenetic variation revealed by this study have shed light on the domestication history of cultivated ginseng, which may serve as a framework for future genetic improvements.

A simple strategy for development of single nucleotide polymorphisms from non-model species and its application in Panax.

Single nucleotide polymorphisms (SNPs) are widely employed in the studies of population genetics, molecular breeding and conservation genetics. In this study, we explored a simple route to develop SNPs from non-model species based on screening the library of single copy nuclear genes (SCNGs). Through application of this strategy in Panax, we identified 160 and 171 SNPs from P. quinquefolium and P. ginseng, respectively. Our results demonstrated that both P. ginseng and P. quinquefolium possessed a high level of nucleotide diversity. The number of haplotype per locus ranged from 1 to 12 for P. ginseng and from 1 to 9 for P. quinquefolium, respectively. The nucleotide diversity of total sites (πT) varied between 0.000 and 0.023 for P. ginseng and 0.000 and 0.035 for P. quinquefolium, respectively. These findings suggested that this approach is well suited for SNP discovery in non-model organisms and is easily employed in standard genetics laboratory studies.