The complete chloroplast genome of Castanopsis hystrix Hook. f. & Thomson ex A. DC. 1863 (Fagaceae)

Abstract Castanopsis hystrix Hook. f. & Thomson ex A. DC. 1863 (Fagaceae) is an evergreen broad-leaved tree with high economic and ecological value. In this study, the complete chloroplast genome of C. hystrix was sequenced, assembled and annotated. The plastome (plastid genome) of C. hystrix was 160,624 bp in size, consisting of a pair of inverted repeats (IRs, 25,699 bp), a large-single-copy (LSC, 90,276 bp) region, and a small-single-copy (SSC, 18,950 bp). The overall GC content of C. hystrix was 36.8%. A total of 133 genes were annotated, including 88 protein-coding genes (PCG), 37 transfer RNA genes (tRNA), and eight ribosomal RNA genes (rRNA). A maximum likelihood analysis showed that the Castanopsis species form a monophyletic clade. C. hystrix is most closely related to C. tibetana with 100% bootstrap support value. The result enriches the genomic data for the genus Castanopsis, which will contribute to future studies in phylogenetics and evolution.


Introduction
Castanopsis hystrix Hook.f. & Thomson ex A. DC.1863, an evergreen broad-leaved tree belonging to the family Fagaceae, is mainly distributed in low altitude areas of tropical and subtropical Asia (Huang et al. 1999).Its timber can be used in furniture production, the shipbuilding industry, and infrastructure construction.The seeds of this species are the preferred material for making wine and feed (Zhou 2007).The abundant litterfall of C. hystrix helps maintain the global carbon cycle in forest ecosystems (Liu et al. 2012).Genomic characterization is the most essential step in breeding programs.However, the genomic information of C. hystrix is poorly understood.In this study, the chloroplast genome of C. hystrix was sequenced, which can provide a reference for exploration, utilization and conservation and provide basic genetic resources for further genetic and phylogenetic studies.

Materials and methods
Fresh and mature leaves of Castanopsis hystrix (Figure 1) were obtained with permission from the Guangxi Forestry Research Institute (latitude 22.93 N, longitude 108.36E), and voucher specimen (collection number: 20210317001) was kept at the Guangxi Forestry Research Institute (http://www.gxlky.com.cn/index.php?siteid=6, Hui Zhu, gfrizhuhui@163.com).Total genomic DNA was extracted using a DNeasy Plant Mini Kit (Qiagen, Germany).The library with insert sizes of 300-500 bp was constructed and sequenced on the Illumina HiSeq X Ten platform (San Diego, USA) at Novogene (Beijing, China).Approximately 2 Gb of clean data was obtained after filtering the adaptors

Discussion and conclusion
Castanopsis is one of the three largest genera in the Fagaceae family (Huang et al. 2023).However, the phylogenetic relationship and species identification remain poorly resolved due to phenotypic diversity, coupled with hybridization issue.Plastome data could be an ideal tool in resolving the phylogenetic relationships and species identification.Castanopsis hystrix is of great economic and ecological value.In this study, the chloroplast genome of C. hystrix has been sequenced, assembled and annotated.The structural characteristics of C. hystrix is similar to most angiosperm, which shows the typical four parts, consisting of a pair of inverted repeats, a large-single-copy region, and a small-single-copy (Palmer 1985).By comparing with previously known genomes of C. hystrix, the high-level conserved chloroplast genome was confirmed which could be demonstrated as a super-DNA barcode to distinguish C. hystrix from the related Castanopsis species.Additionally, the presumably misidentification of C.

Figure 1 .
Figure 1.The photograph of Castanopsis hystrix.This image was taken by Hui Zhu at Guangxi Forestry Research Institute, Nanning Guangxi, China.C. hystrix is an evergreen broad-leaved tree with leaf blade margin shallowly, serrate from middle to apex, secondary veins usually not reaching margin and petiole rarely longer than 1 cm.

Figure 2 .
Figure 2. The complete chloroplast genome map of Castanopsis hystrix, which was generated by CPGview.LSC, SSC, and IR (IRa and IRb) with their length are represented on the first circle.The second circle shows the GC ratio in dark gray.The third circle displays the genes with the colors based on their functional classification presented at the left of the circular map.Genes located on the inner are transcribed in a clockwise, and those outer of circle are transcribed in an anticlockwise.