Deciphering tea tree chloroplast and mitochondrial genomes of Camellia sinensis var. assamica

Abstract

Tea is the most popular non-alcoholic caffeine-containing and the oldest beverage in the world. Despite its enormous industrial, cultural and medicinal values, the chloroplast (cp) and mitochondrial (mt) genomes are not available for Camellia sinensis var. assamica. In this study, we de novo assembled the cp genome sequence of C. sinensis var. assamica into a circular contig of 157,100 bp in length with an overall GC content of 37.29%, comprising a large single-copy region (LSC, 86,649 bp) and a small single-copy region (SSC, 18,285 bp) separated by a pair of inverted repeats (IRs, 26,083 bp). We annotated a total of 141 cp genes, of which 87 are protein-coding genes, 46 are tRNA genes, and eight are rRNA genes. We also de novo assembled the mt genome of C. sinensis var. assamica into two complete circular scaffolds (702,253 bp and 178,082 bp) with overall GC contents of 45.63% and 45.81%, respectively. We annotated a total of 71 mt genes, including 44 protein-coding genes, 24 tRNAs, and 3 rRNAs. Comparative analysis suggests repeat-rich nature of the mt genome compared to the cp genome, for example, with the characterization of 37,878 bp and 149 bp of long repeat sequences and 665 and 214 SSRs, respectively. We also detected 478 RNA-editing sites in 42 protein-coding mt genes, which are [~]4.4-fold more than 54 RNA-editing sites detected in 21 protein-coding cp genes. The high-quality cp and mt genomes of C. sinensis var. assamica presented in this study will become an invaluable resource for a range of genetic, functional, evolutionary and comparative genomic studies in tea tree and other Camellia species of the Theaceae family.