Tea-oil Camellia is one of the four woody oil crops in the world and has high ecological, economic and medicinal values. However, there are great differences in the classification and merging of tea-oil Camellia Sect. Oleifera species, which brings difficulties to the innovative utilization and production of tea-oil Camellia resources. Here, ISSR, SRAP and chloroplast sequence markers were analyzed in 18 populations of tea-oil Camellia Sect. Oleifera species to explore their phylogenetic relationships and genetic diversity. The results showed that their genetic diversity were low, with mean H and π values of 0.16 and 0.00140, respectively. There was high among-population genetic differentiation, with ISSR and SRAP markers showing an Fst of 0.38 and a high Nm of 1.77 and cpDNA markers showing an Fst of 0.65 and a low Nm of 0.27. The C. gauchowensis, C. vietnamensis and Hainan Island populations formed a single group, showing the closest relationships, and supported being the same species for them with the unifying name C. drupifera and classifying the resources on Hainan Island as C. drupifera. The tea-oil Camellia resources of Hainan Island should be classified as a special ecological type or variety of C. drupifera. However, cpDNA marker-based STRUCTURE analysis showed that the genetic components of the C. osmantha population formed an independent, homozygous cluster; hence, C. osmantha should be a new species in Sect. Oleifera. The C. oleifera var. monosperma and C. oleifera populations clustered into two distinct clades, and the C. oleifera var. monosperma populations formed an independent cluster, accounting for more than 99.00% of its genetic composition; however, the C. oleifera populations contained multiple different cluster components, indicating that C. oleifera var. monosperma significantly differs from C. oleifera and should be considered the independent species C. meiocarpa. Haplotype analysis revealed no rapid expansion in the tested populations, and the haplotypes of C. oleifera, C. meiocarpa and C. osmantha evolved from those of C. drupifera. Our results support the phylogenetic classification of Camellia subgenera, which is highly significant for breeding and production in tea-oil Camellia.

Tea-oil Camellia within the genus Camellia is renowned for its premium Camellia oil, often described as “Oriental olive oil”. So far, only one partial mitochondrial genomes of Tea-oil Camellia have been published (no main Tea-oil Camellia cultivars), and comparative mitochondrial genomic studies of Camellia remain limited. In this study, we first reconstructed the entire mitochondrial genome of C. drupifera to gain insights into its genetic structure and evolutionary history. Through our analysis, we observed a characteristic multi-branched configuration in the mitochondrial genomes of C. drupifera. A thorough examination of the protein-coding regions (PCGs) across Camellia species identified gene losses that occurred during their evolution. Notably, repeat sequences showed a weak correlation between the abundance of simple sequence repeats (SSRs) and genome size of Camellia. Additionally, despite of the considerable variations in the sizes of Camellia mitochondrial genomes, there was little diversity in GC content and gene composition. The phylogenetic tree derived from mitochondrial data was inconsistent with that generated from chloroplast data. In conclusion, our study provides valuable insights into the molecular characteristics and evolutionary mechanisms of multi-branch mitochondrial structures in Camellia. The high-resolution mitogenome of C. drupifera enhances our understanding of multi-branch mitogenomes and lays a solid groundwork for future advancements in genomic improvement and germplasm innovation within Tea-oil Camellia.

Tea-oil Camellia, a prominently woody oil crop, serves as a crucial source of edible oil, protein feed, and industrial raw materials. Notably, C. Oleifera and C. meiocarpa yield higher oil production and larger cultivation areas than other Tea-oil Camellia species. However, the taxonomy and phylogenetic relationship between these species remains elusive, complicating their commercial application. Here, we sequenced and analyzed the complete chloroplast genomes of these two species, compared them with related Camellia species, and developed chloroplast DNA markers to distinguish between them. The chloroplast genome of C. Oleifera was 157,009 bp (HZP) and C. meiocarpa was 156,549 bp (CKX) and 156,512 bp (XG) in length. Comparative analysis indicated that distinct differences in the chloroplast genome between HZP and CKX (or XG) than between CKX and XG. The repetitive sequences and interspecific variations among them showed that the differences in the number and distribution in CKX and XG were smaller than those in HZP. Phylogenetic analysis showed that C. meiocarpa was not closely related to C. oleifera. A total of 56 pairs of primers were developed to test the polymorphism among them. After PCR and sequencing verification, variations were detected in the target sequences of 17 primers. The data derived from the chloroplast genomes and the newly developed markers are invaluable for understanding the phylogenetic relationships and assessing the genetic diversity of tea-oil Camellia germplasm resources.

Polyploidization promotes the functional diversification of autophagy in plants, expanding autophagy‐associated genes (AAGs) to support processes like chloroplast division and flowering. Analysis of 92,967 AAGs in Arabidopsis thaliana, Solanum lycopersicum, Camellia oleifera, and 74 other plant species shows that 45.69% of AAGs are polyploidy‐related, highlighting polyploidy's role in linking autophagy to plant‐specific functions.

Introduction: Tea-oil Camellia species play a crucial economic and ecological role worldwide, yet their mitochondrial genomes remain largely unexplored.Methods: In this study, we assembled and analyzed the complete mitochondrial genomes of Camellia oleifera and C. meiocarpa, revealing multi-branch structures that deviate from the typical circular mitochondrial genome observed in most plants. The assembled mitogenomes span 953,690 bp (C. oleifera) and 923,117 bp (C. meiocarpa), containing 74 and 76 annotated mitochondrial genes, respectively.Results: Comparative genomic analyses indicated that C. oleifera and C. meiocarpa share a closer genetic relationship, whereas C. drupifera is more distantly related. Codon usage analysis revealed that natural selection plays a dominant role in shaping codon bias in these mitochondrial genomes. Additionally, extensive gene transfer events were detected among the three species, highlighting the dynamic nature of mitochondrial genome evolution in Tea-oil Camellia. Phylogenetic reconstruction based on mitochondrial genes exhibited incongruence with chloroplast phylogenies, suggesting potential discordance due to hybridization events, incomplete lineage sorting (ILS), or horizontal gene transfer (HGT). Furthermore, we identified species-specific mitochondrial markers, which provide valuable molecular tools for distinguishing Tea-oil Camellia species.Discussion: Our findings enhance the understanding of mitochondrial genome evolution and genetic diversity in Tea-oil Camellia, offering essential genomic resources for phylogenetics, species identification, and evolutionary research in woody plants.