Abstract
Phylogenetic analyses of complete chloroplast genome sequences have yielded significant improvements in our understanding of relationships in the woody flowering genus Viburnum (Adoxaceae, Dipsacales); however, these relationships were evaluated focusing only on Viburnum species within Central and South America and Southeast Asia. By contrast, despite being a hotspot of Viburnum diversity, phylogenetic relationships of Viburnum species in China are less well known. Here, we characterized the complete chloroplast (cp) genomes of 21 Viburnum species endemic to China, as well as three Sambucus species. These 24 plastomes were highly conserved in genomic structure, gene order and content, also when compared with other Adoxaceae. The identified repeat sequences, simple sequence repeats (SSRs) and highly variable plastid regions will provide potentially valuable genetic resources for further population genetics and phylogeographic studies on Viburnum and Sambucus. Consistent with previous combined phylogenetic analyses of 113 Viburnum species, our phylogenomic analyses based on the complete cp genome sequence dataset confirmed the sister relationship between Viburnum and the Sambucus-Adoxa-Tetradoxa-Sinadoxa group, the monophyly of four recognized sections in Flora of China (i.e., Viburnum sect. Tinus, Viburnum sect. Solenotinus, Viburnum sect. Viburnum and Viburnum sect. Pseudotinus) and the nonmonophyly of Viburnum sect. Odontotinus and Viburnum sect. Megalotinus. Additionally, our study confirmed the sister relationships between the clade Valvatotinus and Viburnum sect. Pseudotinus, as well as between Viburnum sect. Opulus and the Odontotinus-Megalotinus group. Overall, our results clearly document the power of the complete cp genomes in improving phylogenetic resolution, and will contribute to a better understanding of plastome evolution in Chinese Adoxaceae.
Highlights
The eudicot family Adoxaceae (Dipsacales) sensu APG IV contains three small herbaceous genera (i.e., Adoxa, Sinadoxa, and Tetradoxa) and two larger genera (i.e., Viburnum and Sambucus) [1]
The results showed that the assembly sequences were totally identical with the PCR amplified fragments, demonstrating the high quality of our assembly
This work presents a major advance in understanding Chinese Adoxaceae phylogenetics and plastome evolution with a particular focus on the genus Viburnum
Summary
The eudicot family Adoxaceae (Dipsacales) sensu APG IV contains three small herbaceous genera (less than 10 species) (i.e., Adoxa, Sinadoxa, and Tetradoxa) and two larger genera (i.e., Viburnum and Sambucus) [1]. The woody flowering taxon Viburnum, with approximately 200 species of shrubs and small trees [2], is the largest genus within Adoxaceae, and is of great interest to the horticultural community, since more than 70 of these species (and a variety of artificial hybrids) have been brought into cultivation [3]. Sambucus is a relatively small genus occurring mostly in the north temperate zone, comprising about 10 species of small trees, shrubs and perennial herbs [5,9,10], of which many species are cultivated ornamentally, and several. Within Adoxaceae, analyses of complete cp genome sequences suggested that Sambucus and Viburnum were the most closely related [12]; Viburnum was likely to be the sister group of Sambucus plus
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