Genomic and Phylogenetic analysis of Mitochondrial Genomes in three main Tea-oil Camellia (Camellia spp.) species of China, a high economic development value plant

Tea-oil Camellia species offer significant benefits globally. Despite this, only one complete mitochondrial genome of C. drupifera from this group has been reported, and comparative studies among the main species are lacking. The present study explores the mitochondrial DNA (mtDNA) of C. oleifera and C. meiocarpa, which both exhibit a multi-branch structure deviating from the traditional circular form. The mtDNA measures 953,690 bp (C. oleifera) and 923,117 bp (C. meiocarpa) in length, respectively, with 74 and 76 annotated mitochondrial genes. Our comprehensive analysis reveals that C. oleifera and C. meiocarpa share a closer genetic relationship, while C. drupifera is more distantly related. The examination of the effective number of codons (ENC) reveals that natural selection is the primary factor influencing codon usage bias in the mtDNA of these species. Additionally, we identified numerous gene transfer sequences across the three species. The variations in these mtDNA show potential for use as molecular indicators in classification studies. Additionally, genomic and phylogenetic analysis indicates that C. oleifera is genetically more similar to C. meiocarpa than to C. drupifera. Our findings provide essential molecular resources for understanding the genetic characteristics of Tea-oil Camellia and offer new evidence to advance evolutionary research on Camellia and other related woody species.