Comparative Plastid Genomes of Primula Species: Sequence Divergence and Phylogenetic Relationships

Compared to traditional DNA markers, genome-scale datasets can provide mass information to effectively address historically difficult phylogenies. Primula is the largest genus in the family Primulaceae, with members distributed mainly throughout temperate and arctic areas of the Northern Hemisphere. The phylogenetic relationships among Primula taxa still maintain unresolved, mainly due to intra- and interspecific morphological variation, which was caused by frequent hybridization and introgression. In this study, we sequenced and assembled four complete plastid genomes (Primula handeliana, Primula woodwardii, Primula knuthiana, and Androsace laxa) by Illumina paired-end sequencing. A total of 10 Primula species (including 7 published plastid genomes) were analyzed to investigate the plastid genome sequence divergence and their inferences for the phylogeny of Primula. The 10 Primula plastid genomes were similar in terms of their gene content and order, GC content, and codon usage, but slightly different in the number of the repeat. Moderate sequence divergence was observed among Primula plastid genomes. Phylogenetic analysis strongly supported that Primula was monophyletic and more closely related to Androsace in the Primulaceae family. The phylogenetic relationships among the 10 Primula species showed that the placement of P. knuthiana–P. veris clade was uncertain in the phylogenetic tree. This study indicated that plastid genome data were highly effective to investigate the phylogeny.