Abstract
BackgroundPanax L. is a medicinally important genus within family Araliaceae, where almost all species are of cultural significance for traditional Chinese medicine. Previous studies suggested two independent origins of the East Asia and North America disjunct distribution of this genus and multiple rounds of whole genome duplications (WGDs) might have occurred during the evolutionary process.ResultsWe employed multiple chloroplast and nuclear markers to investigate the evolution and diversification of Panax. Our phylogenetic analyses confirmed previous observations of the independent origins of disjunct distribution and both ancient and recent WGDs have occurred within Panax. The estimations of divergence time implied that the ancient WGD might have occurred before the establishment of Panax. Thereafter, at least two independent recent WGD events have occurred within Panax, one of which has led to the formation of three geographically isolated tetraploid species P. ginseng, P. japonicus and P. quinquefolius. Population genetic analyses showed that the diploid species P. notoginseng harbored significantly lower nucleotide diversity than those of the two tetraploid species P. ginseng and P. quinquefolius and the three species showed distinct nucleotide variation patterns at exon regions.ConclusionOur findings based on the phylogenetic and population genetic analyses, coupled with the species distribution patterns of Panax, suggested that the two rounds of WGD along with the geographic and ecological isolations might have together contributed to the evolution and diversification of this genus.Electronic supplementary materialThe online version of this article (doi:10.1186/s12870-015-0669-0) contains supplementary material, which is available to authorized users.
Highlights
Panax L. is a medicinally important genus within family Araliaceae, where almost all species are of cultural significance for traditional Chinese medicine
Based on the phylogenetic tree and chromosome number, Yi et al [31] have proposed that at least two recent polyploidy events have occurred within the genus Panax, one of which has led to the formation of three geographically isolated tetraploid (2n = 48) species P. ginseng, P. japonicus and P. quinquefolius
In Panax, previous studies based on the expressed sequence tags (ESTs) indicated that the extant tetraploid species, P. ginseng and P. quinquefolius, have undergone two rounds of whole genome duplications (WGDs), of which, the first round of WGD had occurred during 24.6–32.8 million years ago (MYA) [34, 35]
Summary
Panax L. is a medicinally important genus within family Araliaceae, where almost all species are of cultural significance for traditional Chinese medicine. Based on the phylogenetic tree and chromosome number, Yi et al [31] have proposed that at least two recent polyploidy events have occurred within the genus Panax, one of which has led to the formation of three geographically isolated tetraploid (2n = 48) species P. ginseng, P. japonicus and P. quinquefolius. The other recent polyploidy event had occurred within the P. bipinnatifidus species complex wherein both diploids (2n = 24) and tetraploids are identified These previous studies provide a framework for understanding the evolutionary history of genus Panax. Recent investigations based on the expressed sequence tags (ESTs) suggested that the tetraploid species P. ginseng and P. quinquefolius have experienced two rounds of WGD and diverged to each other after the recent tetraploidization event [34, 35] These features suggested that the evolutionary trajectories of Panax species are much more complicated than we thought
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