Complete chloroplast genome of Castanopsis sclerophylla (Lindl.) Schott: Genome structure and comparative and phylogenetic analysis

The complete chloroplast genome assembly of Castanopsis orthacantha Franch. 1899 (Fagaceae) in Southwestern China

Castanopsis orthacantha Franch. 1899 is one representative tree species distributed in the evergreen broad-leaved forests of southwestern China. This species is an important source of timber for manufacturing furniture, floors, and paper. It also plays a significant role in maintaining ecological balance and stability. To help with the genetic diversity assessment of C. orthacantha, we sequenced and assembled the first complete chloroplast genome. The length of the chloroplast genome was 160,588 bp, with a typical quadripartite structure (GenBank accession no. OR900101). The large single-copy (LSC), small single-copy (SSC), and two inverted repeats (IRs) were 90,237 bp, 18,953 bp, and 25,699 bp in length, respectively. We annotated one hundred and thirty genes across the chloroplast genome, including 86 protein-coding genes (79 are unique), 37 tRNA genes (29 are unique), and eight rRNA genes (four are unique). Seventeen genes had one intron, and four were detected with two introns. The maximum likelihood phylogeny suggested that C. orthacantha, C. lamontii, C. sclerophylla, and C. hainanensis formed a clade with a high bootstrap value. This newly sequenced chloroplast genome assembly will aid in the population genetic and phylogenetic studies of Castanopsis species in the future.

Hierarchy of codon usage frequencies from codon-anticodon interaction in the crystal basis model

Analyzing the codon usage frequencies of a specimen of 20 plants, for which the codon-anticodon pattern is known, we have remarked that the hierarchy of the usage frequencies present an almost "universal" behavior. Searching to explain this behavior, we assume that the codon usage probability results from the sum of two contributions: the first dominant term is an almost "universal" one and it depends on the codon-anticodon interaction; the second term is a local one, i.e. depends on the biological species. The codon-anticodon interaction is written as a spin-spin plus a z-spin term in the formalism of the crystal basis model. From general considerations, in particular from the choice of the signs and some constraints on the parameters defining the interaction, we are able to explain most of the observed data.

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

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.

The characteristic of the complete chloroplast genome of Lithocarpus konishii (Fagaceae), a rare and endemic species in South China

Lithocarpus konishii, a rare species endemic to islands in South China, was evaluated as a vulnerable species (VU) by the 'China Species Red List.' Here, we first presented the complete chloroplast genome sequence of L. konishii. The chloroplast genome was 161,059 bp in length with 36.76% GC content, containing a small single-copy region (SSC, 18,967 bp), a large single-copy region (LSC, 90,250 bp), and a pair of inverted repeats (IRs, 25,921 bp each). A total of 139 genes were predicted, including 87 protein-coding genes (CDS), 8 rRNAs, and 44 tRNAs. Based on the concatenated shared unique CDS sequence dataset, maximum-likelihood and Bayesian inference methods were used to build the phylogenetic trees of 18 species from the Fagaceae family. Results indicated that L. konishii is closely related to L. longnux and L. pachyphyllus var. fruticosus, and forms a monophyly of the subfamily Castaneoideae with Castanopsis and Castanea. This study provides a theoretical basis for the conservation genomics of this endangered plant.

Chloroplast Genomes of Genus Tilia: Comparative Genomics and Molecular Evolution

Tilia is a complex genus in the family Malvaceae that has high ecological and economical values. Owing to the lack of sufficient distinguishable morphological and molecular characteristics, interspecific relationships in this genus are not clear. Chloroplast (cp) genomes are small, meanwhile most angiosperms usually undergo matrilineal inheritance. Consequently, they can be used in molecular systematics and phylogenetic analyses. Here, we sequenced and assembled cp genomes from T. endochrysea, T. tomentosa, T. miqueliana, T. americana and T. cordata, and compared them with those of seven previously reported Tilia species. Similar gene contents, gene orders and GC contents existed among the 12 cp genomes, which ranged from 162,564 to 162,855 bp and encoded 113 unique genes. Abundant simple sequence repeats (119–127) and dispersed repeats (97–135) were detected in Tilia cp genomes. In total, 11 hypervariable regions were identified that could be suitable for species identification and phylogenetic studies. A phylogenetic analysis of Malvaceae based on 5 hypervariable genes (matK + ndhF + rpoB + rpoC2+ycf1) revealed that all eight subfamilies were monophyletic groups. Additionally, the genus Tilia was divided into three groups on the basis of all 521 molecular variation loci. The current study provides valuable insights into the genomic evolution of the genus Tilia.

Chloroplast Genome of Lithocarpus dealbatus (Hook.f. & Thomson ex Miq.) Rehder Establishes Monophyletic Origin of the Species and Reveals Mutational Hotspots with Taxon Delimitation Potential

There is phylogenetic ambiguity in the genus Lithocarpus and subfamily Quercoideae (Family: Fagaceae). Lithocarpus dealbatus, an ecologically important tree, is the dominant species among the Quercoideae in India. Although several studies have been conducted on the species' regeneration and ecological and economic significance, limited information is available on its phylo-genomics. To resolve the phylogeny in Quercoideae, we sequenced and assembled the 161,476 bp chloroplast genome of L. dealbatus, which has a large single-copy section of 90,732 bp and a small single-copy region of 18,987 bp, separated by a pair of inverted repeat regions of 25,879 bp. The chloroplast genome contained 133 genes, of which 86 were protein-coding genes, 39 were transfer RNAs, and eight were ribosomal RNAs. Analysis of repeat elements and RNA editing sites revealed interspecific similarities within the Lithocarpus genus. DNA diversity analysis identified five highly diverged coding and noncoding hotspot regions in the four genera, which can be used as polymorphic markers for species/taxon delimitation across the four genera of Quercoideae viz., Lithocarpus, Quercus, Castanea, and Castanopsis. The chloroplast-based phylogenetic analysis among the Quercoideae established a monophyletic origin of Lithocarpus, and a closer evolutionary lineage with a few Quercus species. Besides providing insights into the chloroplast genome architecture of L. dealbatus, the study identified five mutational hotspots having high taxon-delimitation potential across four genera of Quercoideae.

Chloroplast genomes of two Pueraria DC. species: sequencing, comparative analysis and molecular marker development

Puerariae lobatae radix (Ge‐Gen in Chinese) and Puerariae thomsonii radix (Fen‐Ge) are widely used as medicine and health products, particularly in Chinese medicine. Puerarin and daidzein are the primary bioactive compounds in Puerariae radix. These isoflavones have been used to treat cardiovascular and cerebrovascular diseases, hypertension, diabetes, and osteoporosis. The content of puerarin in Ge‐Gen is about six times higher than that in Fen‐Ge, so its use has a higher pharmacological effect. It is therefore of great importance to effectively distinguish between these two species. However, because their basal plants, P. lobata (Willd.) Ohwi and P. thomsonii Benth., possess an extremely similar appearance, and detecting the level of chemical constituents is just a rough distinction, it is necessary to develop more efficient identification approaches. Here the complete chloroplast genomes of P. lobata and P. thomsonii were deciphered, including sequencing, assembly, comparative analysis, and molecular marker development. The results showed that they are 153,393 and 153,442 bp in length, respectively; both contain 124 annotated genes, including eight encoding rRNA, 29 encoding tRNA, and 87 encoding proteins. Phylogenetic analysis showed that they form a clade, indicating that they originate from the same ancestor. After obtaining 10 intergenic/intronic regions with a genetic distance greater than 0.5 cm, primers were designed to amplify regions of high variability in P. lobata and P. thomsonii. Finally, a 60‐bp differential base fragment, located in the intron of rpl16, was developed as a molecular marker to efficiently distinguish between these two species.

Complete Chloroplast Genomes of Vachellia nilotica and Senegalia senegal: Comparative Genomics and Phylogenomic Placement in a New Generic System

Vachellia and Senegalia are the most important genera in the subfamily Mimosoideae (Fabaceae). Recently, species from both genera were separated from the long-characterized Acacia due to their macro-morphological characteristics. However, this morpho-taxonomic differentiation struggles to discriminate some species, for example, Vachellia nilotica and Senegalia senegal. Therefore, sequencing the chloroplast (cp) genomes of these species and determining their phylogenetic placement via conserved genes may help to validate the taxonomy. Hence, we sequenced the cp genomes of V. nilotica and S. senegal, and the results showed that the sizes of the genomes are 165.3 and 162.7 kb, respectively. The cp genomes of both species comprised large single-copy regions (93,849~91,791 bp) and pairs of inverted repeats (IR; 26,093~26,008 bp). The total numbers of genes found in the V. nilotica and S. senegal cp genomes were 135 and 132, respectively. Approximately 123:130 repeats and 290:281 simple sequence repeats were found in the S. senegal and V. nilotica cp genomes, respectively. Genomic characterization was undertaken by comparing these genomes with those of 17 species belonging to related genera in Fabaceae. A phylogenetic analysis of the whole genome dataset and 56 shared genes was undertaken by generating cladograms with the same topologies and placing both species in a new generic system. These results support the likelihood of identifying segregate genera from Acacia with phylogenomic disposition of both V. nilotica and S. senegal in the subfamily Mimosoideae. The current study is the first to obtain complete genomic information on both species and may help to elucidate the genome architecture of these species and evaluate the genetic diversity among species.