Complete chloroplast genome of Camellia japonica genome structures, comparative and phylogenetic analysis

Camellia is an economically, ecologically and phylogenetically valuable genus in the family Theaceae. The frequent interspecific hybridization and polyploidization makes this genus phylogenetically and taxonomically under controversial and require detailed investigation. Chloroplast (cp) genome sequences have been used for cpDNA marker development and genetic diversity evaluation. Our research newly sequenced the chloroplast genome of Camellia japonica using Illumina HiSeq X Ten platform, and retrieved five other chloroplast genomes of Camellia previously published for comparative analyses, thereby shedding lights on a deeper understanding of the applicability of chloroplast information. The chloroplast genome sizes ranged in length from 156,607 to 157,166 bp, and their gene structure resembled those of other higher plants. There were four categories of SSRs detected in six Camellia cpDNA sequences, with the lengths ranging from 10 to 17bp. The Camellia species exhibited different evolutionary routes that lhbA and orf188, followed by orf42 and psbZ, were readily lost during evolution. Obvious codon preferences were also shown in almost all protein-coding cpDNA and amino acid sequences. Selection pressure analysis revealed the influence of different environmental pressures on different Camellia chloroplast genomes during long-term evolution. All Camellia species, except C. crapnelliana, presented the identical rate of amplification in the IR region. The datasets obtained from the chloroplast genomes are highly supportive in inferring the phylogenetic relationships of the Camellia taxa, indicating that chloroplast genome can be used for classifying interspecific relationships in this genus.