AS one of the largest genera in the family Asteraceae, Saussurea DC. exhibits extreme morphological diversity and exists in habitats ranging from steppes to moist forests to cold and dry alpine meadows above 5000m. Several phylogenetic studies have been conducted on Saussurea, but the circumscription and infrageneric relationships of the genus remain controversial, mainly because of the low phylogenetic resolution provided by fragmented markers.
The Plant Systematics and Evolution Group of Wuhan Botanical Garden collected the all four subgenera of Saussurea, and conducted the plastome phylogenomics analyses of Saussurea during the investigation of Qinghai-Tibet Plateau (QTP), one of the key high-altitude biodiversity hotspots in the world.
17 species representing all four subgenera of Saussurea were sequenced. All Saussurea plastomes shared the gene content and structure of most Asteraceae plastomes. Most protein coding genes were found to be under purifying selection. Phylogenomic analyses of 20 Saussurea plastomes that alternatively included nucleotide or amino acid sequences of all protein-coding genes, vs. the nucleotide sequence of the entire plastome, supported the monophyly of Saussurea and identified three clades within it. Three of the four traditional subgenera were resolved as paraphyletic.
Phylogenetic results demonstrated that currently accepted subgeneric groups in Saussurea were likely based at least partly on convergent character states, and were therefore in need of revision. In addition, seven plastome regions were identified as containing the highest nucleotide variability and will be useful for further population genetic studies.
In this study, the effectiveness of different positions and sequences of plastomes on the phylogenetic study of radiating taxa were investigated by generating different data sets, which provided a new vision for plastome phylogenomics.
This work was supported by the Strategic Priority Research Program of Chinese Academy of Sciences, the National Key R&D Program of China. Relevant research results have been published in BMC Plant Biology entitled “Plastome phylogenomics of Saussurea (Asteraceae: Cardueae)”