The Complete Plastid Genome of Rhododendron pulchrum and Comparative Genetic Analysis of Ericaceae Species

Background and Objectives:Rhododendron pulchrum Sweet (R. pulchrum) belongs to the genus Rhododendron (Ericaceae), a valuable horticultural and medicinal plant species widely used in Western Europe and the US. Despite its importance, this is the first member to have its cpGenome sequenced. Materials and Methods: In this study, the complete cp genome of R. pulchrum was sequenced with NGS Illumina HiSeq2500, analyzed, and compared to eight species in the Ericaceae family. Results: Our study reveals that the cp genome of R. pulchrum is 136,249 bp in length, with an overall GC content of 35.98% and no inverted repeat regions. The R. pulchrum chloroplast genome encodes 73 genes, including 42 protein-coding genes, 29 tRNA genes, and two rRNA genes. The synonymous (Ks) and nonsynonymous (Ka) substitution rates were estimated and the Ka/Ks ratio of R. pulchrum plastid genes were categorized; the results indicated that most of the genes have undergone purifying selection. A total of 382 forward and 259 inverted long repeats, as well as 221 simple-sequence repeat loci (SSR) were detected in the R. pulchrum cp genome. Comparison between different Ericaceae cp genomes revealed significant differences in genome size, structure, and GC content. Conclusions: The phylogenetic relationships among eight Ericaceae species suggested that R. pulchrum is closely related to Vaccinium oldhamii Miq. and Vaccinium macrocarpon Aiton. This study provides a theoretical basis for species identification and future biological research of Rhododendron resources.