Complete chloroplast genome of Castanopsis sclerophylla (Lindl.) Schott: Genome structure and comparative and phylogenetic analysis

Castanopsis sclerophylla (Lindl.) Schott is an important species of evergreen broad-leaved tree in subtropical areas and has high ecological and economic value. However, there are few studies on its chloroplast genome. In this study, the complete chloroplast genome sequence of C. sclerophylla was determined using the Illumina HiSeq 2500 platform. The complete chloroplast genome of C. sclerophylla is 160,497 bp long, including a pair of inverted repeat (IR) regions (25,675 bp) separated by a large single-copy (LSC) region of 90,255 bp and a small single-copy (SSC) region of 18,892 bp. The overall GC content of the chloroplast genome is 36.82%. A total of 131 genes were found; of these, 111 genes are unique and annotated, including 79 protein-coding genes, 27 transfer RNA genes (tRNAs), and four ribosomal RNA genes (rRNAs). Twenty-one genes were found to be duplicated in the IR regions. Comparative analysis indicated that IR contraction might be the reason for the smaller chloroplast genome of C. sclerophylla compared to three congeneric species. Sequence analysis indicated that the LSC and SSC regions are more divergent than IR regions within Castanopsis; furthermore, greater divergence was found in noncoding regions than in coding regions. The maximum likelihood phylogenetic analysis showed that four species of the genus Castanopsis form a monophyletic clade and that C. sclerophylla is closely related to Castanopsis hainanensis with strong bootstrap values. These results not only provide a basic understanding of Castanopsis chloroplast genomes, but also illuminate Castanopsis species evolution within the Fagaceae family. Furthermore, these findings will be valuable for future studies of genetic diversity and enhance our understanding of the phylogenetic evolution of Castanopsis.