Phylogenomic analyses of Camellia support reticulate evolution among major clades

Yerba mate (Ilex paraguariensis) genome provides new insights into convergent evolution of caffeine biosynthesis

Yerba mate (YM, Ilex paraguariensis) is an economically important crop marketed for the elaboration of mate, the third-most widely consumed caffeine-containing infusion worldwide. Here, we report the first genome assembly of this species, which has a total length of 1.06 Gb and contains 53,390 protein-coding genes. Comparative analyses revealed that the large YM genome size is partly due to a whole-genome duplication (Ip-α) during the early evolutionary history of Ilex, in addition to the hexaploidization event (γ) shared by core eudicots. Characterization of the genome allowed us to clone the genes encoding methyltransferase enzymes that catalyse multiple reactions required for caffeine production. To our surprise, this species has converged upon a different biochemical pathway compared to that of coffee and tea. In order to gain insight into the structural basis for the convergent enzyme activities, we obtained a crystal structure for the terminal enzyme in the pathway that forms caffeine. The structure reveals that convergent solutions have evolved for substrate positioning because different amino acid residues facilitate a different substrate orientation such that efficient methylation occurs in the independently evolved enzymes in YM and coffee. While our results show phylogenomic constraint limits the genes coopted for convergence of caffeine biosynthesis, the X-ray diffraction data suggest structural constraints are minimal for the convergent evolution of individual reactions.

Phylotranscriptomics resolved phylogenetic relationships and divergence time between 20 golden camellia species

Golden camellia species are endangered species with great ecological significance and economic value in the section Chrysantha of the genus Camellia of the family Theaceae. Literature shows that more than 50 species of golden camellia have been found all over the world, but the exact number remains undetermined due to the complex phylogenetic background, the non-uniform classification criteria, and the presence of various synonyms and homonyms; and phylogenetic relationships among golden camellia species at the gene level are yet to be disclosed. Therefore, it is necessary to investigate the divergence time and phylogenetic relationships between all golden camellia species at the gene level to improve their classification system and achieve accurate identification of them. Phenotypic data and transcriptomic sequences of 20 golden camellia species commonly found in Guangxi, China were obtained. PCA and OPLS-DA analyses were conducted based on phenotypic data, and agglomerative clustering was performed to generate the clustering tree of the 20 golden camellia species. Single-copy homologous genes were used to generate phylogenetic trees using Neighbor-Joining, Maximum Likelihood, and Bayesian Inference methods, and the results obtained with these three methods were compared. Then the molecular dating analysis was performed to reveal the divergence time and evolutionary relationships. Rhododendron griersonianum, Diospyros lotus, and Impatiens glandulifera were used as outgroups. The phylogenetic tree based on single-copy homologous genes showed that golden camellia species with shorter geographical distances were closer phylogenetically. Phylogenetic relationships based on phenotypic traits and those based on single-copy homologous genes were inconsistent, suggesting that species with a close genetic evolutionary relationship may show high variation in phenotypic traits and thus the analysis of evolutionary relationships based on phenotypic traits may result in inaccurate outcomes. Among three phylogenetic trees constructed by the three methods, the evolutionary sequences were different, but evolutionary relationships between most species were consistent. For 6 species, the divergence time estimated by Maximum Likelihood and Bayesian Inference varied much, that estimated by Bayesian Inference later than that estimated by Maximum Likelihood. Using these two methods, the resulting divergence time of 14 species was 3.452 Mya. The divergence time predicted in our study is later than that in the literature. In the present study phylogenetic relationships among 20 golden camellia species were analyzed at the transcriptome level to provide a supplement to the phylogenetic classification and evolutionary relationships explored using morphological traits and some molecular markers. Our findings show that the 20 golden camellia species diverged at a later time than other known species in the genus Camellia. Since our analyses were based on the failed molecular clock hypothesis, our conclusions are tentative. Further research using more systematic analyses and more methods should be conducted to confirm the phylogenetic relationships among golden camellia species.

Assembly and analysis of the first complete mitochondrial genome sequencing of main Tea-oil Camellia cultivars Camellia drupifera (Theaceae): revealed a multi-branch mitochondrial conformation for Camellia

BACKGROUND

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.

RESULTS

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.

CONCLUSIONS

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.

Genetic structure and demographic analysis of a true single-population species, Camellia azalea

Single-population species (SPS) consist of only one natural population and often are at high risk of extinction. Although almost all species must go through this special stage in their evolutionary process, there is little understanding of how SPS survives. Camellia azalea C. F. Wei is a typical SPS, and has precious breeding values for its special flowering period. This study surveyed the age structure and spatial distribution of C. azalea, analyzed its genetic diversity and fine-scale spatial genetic structure (SGS) using microsatellite markers for 629 individuals, and estimated the effect of human disturbances on its population dynamics. Results showed that this species had a relatively moderate genetic diversity (I = 0.989, He = 0.509, and Ho = 0.497), high rate of sapling (~ 35%), and a narrow habitat (~ 6 km long, ~ 10 m wide). Although the construction of dams and roads did not lead to a significant loss of genetic diversity and genetic differentiation (FST = 0.0096 ~ 0.0128, Nm = 19 ~ 26), it limited C. azalea's seed flow (adults, 95 m; juveniles, 60 m), which was a reason for juveniles having a stronger SGS than adults. These results indicate that as an SPS, C. azalea still possesses the potential capacity for self-evolution and regeneration, however, it is at risk of extinction due to its small range, narrow habitat, and human distances. Furthermore, the results are also of enlightening significance to the conservation of other SPS, especially those distributed along the riparian zone.

Evolutionary Histories of Camellia japonica and Camellia rusticana

The genus Camellia is widely distributed, primarily in East Asia. Camellia japonica is located at the northern limit of this genus distribution, and understanding changes in its distribution is crucial for understanding the evolution of plants in this region, as well as their relationship with geological history and climate change. Moreover, the classification of sect. Camellia in Japan has not been clarified. Therefore, this study aims to understand the evolutionary history of the Japanese sect. Camellia. The genetic population structure was analysed using SNP data and MIG-seq. The relationship between the Japanese sect. Camellia, including the related species in China, was further inferred from the phylogeny generated by RA x ML, SplitsTree and PCA. Population genetic structure was inferred using a Bayesian clustering method (ADMIXTURE). We subsequently employed approximate Bayesian computation, which was further supported by the coalescent simulations (DIYABC, fastsimcoal and Bayesian Skyline Plots) to explore the changes in population, determining which events appropriately explain the phylogeographical signature. Ecological niche modelling was combined with genetic analyses to compare current and past distributions. The analyses consistently showed that C. japonica and C. rusticana are distinct, having diverged from each other during the Middle to Late Miocene period. Furthermore, C. japonica differentiated into four major populations (North, South, Ryukyu-Taiwan and Continent). The Japanese sect. Camellia underwent speciation during archipelago formation, reflecting its ancient evolutionary history compared with other native Japanese plants. C. rusticana did not diverge from C. japonica in snow-rich environments during the Quaternary period. Our results suggest that both species have been independent since ancient times and that ancestral populations of C. japonica have persisted in northern regions. Furthermore, the C. japonica population on the continent is hypothesised to have experienced a reverse-colonisation event from southern Japan during the late Pleistocene glaciation.

OHDLF: A Method for Selecting Orthologous Genes for Phylogenetic Construction and Its Application in the Genus Camellia

Accurate phylogenetic tree construction for species without reference genomes often relies on de novo transcriptome assembly to identify single-copy orthologous genes. However, challenges such as whole-genome duplication (WGD), heterozygosity, gene duplication, and loss can hinder the selection of these genes, leading to limited data for constructing reliable species trees. To address these issues, we developed a new analytical pipeline, OHDLF (Orthologous Haploid Duplication and Loss Filter), which filters orthologous genes from transcript data and adapts parameter settings based on genomic characteristics for further phylogenetic tree construction. In this study, we applied OHDLF to the genus Camellia and evaluated its effectiveness in constructing phylogenetic trees. The results highlighted the pipeline's ability to handle challenges like high heterozygosity and recent gene duplications by selectively retaining genes with a missing rate and merging duplicates with high similarity. This approach ensured the preservation of informative sites and produced a highly supported consensus tree for Camellia. Additionally, we evaluate the accuracy of the OHDLF phylogenetic trees for different species, demonstrating that the OHDLF pipeline provides a flexible and effective method for selecting orthologous genes and constructing accurate phylogenetic trees, adapting to the genomic characteristics of various plant groups.

A new nuclear phylogeny of the tea family (Theaceae) unravels rapid radiations in genus Camellia

Molecular analyses of rapidly radiating groups often reveal incongruence between gene trees. This mainly results from incomplete lineage sorting, introgression, and gene tree estimation error, which complicate the estimation of phylogenetic relationships. In this study, we reconstruct the phylogeny of Theaceae using 348 nuclear loci from 68 individuals and two outgroup taxa. Sequence data were obtained by target enrichment using the recently released Angiosperm 353 universal probe set applied to herbarium specimens. The robustness of the topologies to variation in data quality was established under a range of different filtering schemes, using both coalescent and concatenation approaches. Our results confirmed most of the previously hypothesized relationships among tribes and genera, while clarifying additional interspecific relationships within the rapidly radiating genus Camellia. We recovered a remarkably high degree of gene tree heterogeneity indicative of rapid radiation in the group and observed cytonuclear conflicts, especially within Camellia. This was especially pronounced around short branches, which we primarily associate with gene tree estimation error. Our analysis also indicates that incomplete lineage sorting (ILS) contributed to gene-tree conflicts and accounted for approximately 14 % of the explained variation, whereas inferred introgression levels were low. Our study advances the understanding of the evolution of this important plant family and provides guidance on the application of target capture methods and the evaluation of key processes that influence phylogenetic discordances.

Camelliazijinica (Theaceae), a new species endemic to Danxia landscape from Guangdong Province, China

A new species of the genus Camellia (Theaceae), Camelliazijinica, discovered in the Danxia landscape from Guangdong Province, China, is characterized and illustrated. Phylogenetic analysis based on chloroplast genomes suggested its affinity with C.drupifera, C.oleifera and C.fluviatilis, however, it morphologically differs from all of the latter by leaf shape and size. Phonologically, it most closely resembles C.microphylla, but can be distinguished from the latter by its young branchlets glabrous (vs. densely pubescent), fewer bracteoles and sepals, diverse leaf shape, midvein raised slightly with sparsely pubescent or glabrous (vs. prominently with densely pubescent) and leaf adaxially matt (vs. vernicose) when dried. By morphological and molecular analyses, Camelliazijinica represented a distinct new species of C.sect.Paracamellia.

Comparative Phylogenetic Analysis of Ancient Korean Tea "Hadong Cheon-Nyeon Cha (Camellia sinensis var. sinensis)" Using Complete Chloroplast Genome Sequences

Wild teas are valuable genetic resources for studying evolution and breeding. Here, we report the complete chloroplast genome of the ancient Korean tea 'Hadong Cheon-nyeon Cha' (C. sinensis var. sinensis), which is known as the oldest tea tree in Korea. This study determined seven Camellia sinensis var. sinenesis, including Hadong Cheon-nyeon Cha (HCNC) chloroplast genome sequences, using Illumina sequencing technology via de novo assembly. The chloroplast genome sizes ranged from 157,019 to 157,114 bp and were organized into quadripartite regions with the typical chloroplast genomes. Further, differences in SNPs and InDels were detected across the seven chloroplast genomes through variance analysis. Principal component and phylogenetic analysis suggested that regional constraints, rather than functional constraints, strongly affected the sequence evolution of the cp genomes in this study. These genomic resources provide evolutionary insight into Korean tea plant cultivars and lay the foundation for a better understanding of the ancient Korean tea plant HCNC.