Comparative and phylogenetic analysis of the complete chloroplast
genomes of Osmanthus (Oleaceae) species
As one genus of Oleaceae, Osmanthus is well-known for its high
ornamental value. Due to the deficiency of clearly discriminatory
traits, the species classification of genus Osmanthus is controversial.
Here, we obtained two chloroplast genomes of O. fragrans and O.
matsumuranus using Illumina sequencing, and compared them with 13
previously published chloroplast genomes of Osmanthus species. The
chloroplast genomes of 15 Osmanthus species were 155,155 to 155,570 bp
in length, which showed a typical quadripartite structure with high
conservation of gene order and gene content. Each chloroplast genome had
132 genes including 87 protein-coding genes, 37 tRNA genes and eight
rRNA genes. The number of simple sequence repeats identified in each
Osmanthus species was in the range of 55-68. A total of 11 highly
variable loci could be potentially used as specific molecular markers in
the identification of Osmanthus species. The third position of codons
tended to use A/U base, and natural selection contributed more in the
formation of codon usage bias in comparison to mutation pressure. The
chloroplast genome phylogenetic analysis showed that the species of
Sect. Leiolea formed a well-supported monophyletic clade sister to
Chionanthus virginicus. Besides, O. austrocaledonicus also separated as
a distinct lineage nested within the members of Notelaea and Nestegis.
The results of comparative and phylogenetic analysis provide valuable
references for further study in identification, breeding improvement and
phylogenetic relationships in Osmanthus species.