Mitochondrial genome variation and intergenomic sequence transfers in Hevea species.

Among the Hevea species, rubber tree (Hevea brasiliensis) is the most important source of natural rubber. In previous studies, we sequenced the complete nuclear and chloroplast genomes of Hevea species, providing an invaluable resource for studying their phylogeny, disease resistance, and breeding. However, given that plant mitochondrial genomes are more complex and more difficult to assemble than that of the other organelles, little is known about their mitochondrial genome, which limits the comprehensive understanding of Hevea genomic evolution. In this study, we sequenced and assembled the mitochondrial genomes of four Hevea species. The four mitochondrial genomes had consistent GC contents, codon usages and AT skews. However, there were significant differences in the genome lengths and sequence repeats. Specifically, the circular mitochondrial genomes of the four Hevea species ranged from 935,732 to 1,402,206 bp, with 34-35 unique protein-coding genes, 35-38 tRNA genes, and 6-13 rRNA genes. In addition, there were 17,294-46,552 bp intergenomic transfer fragments between the chloroplast and mitochondrial genomes, consisting of eight intact genes (psaA, rrn16S, tRNA-Val, rrn5S, rrn4.5S, tRNA-Arg, tRNA-Asp, and tRNA-Asn), intergenic spacer regions and partial gene sequences. The evolutionary position of Hevea species, crucial for understanding its adaptive strategies and relation to other species, was verified by phylogenetic analysis based on the protein-coding genes in the mitochondrial genomes of 21 Malpighiales species. The findings from this study not only provide valuable insights into the structure and evolution of the Hevea mitochondrial genome but also lay the foundation for further molecular, evolutionary studies, and genomic breeding studies on rubber tree and other Hevea species, thereby potentially informing conservation and utilization strategies.

Insights to the superoxide dismutase genes and its roles in Hevea brasiliensis under abiotic stress.

The superoxide dismutase (SOD) protein significantly influences the development and growth of plants and their reaction to abiotic stresses. However, little is known about the characteristics of rubber tree SOD genes and their expression changes under abiotic stresses. The present study recognized 11 SOD genes in the rubber tree genome, including 7 Cu/ZnSODs, 2 MnSODs, and 2 FeSODs. Except for HbFSD1, SODs were scattered on five chromosomes. The phylogenetic analysis of SOD proteins in rubber trees and a few other plants demonstrated that the SOD proteins contained three major subgroups. Moreover, the genes belonging to the same clade contained similar gene structures, which confirmed their classification further. The extension of the SOD gene family in the rubber tree was mainly induced by the segmental duplication events. The cis-acting components analysis showed that HbSODs were utilized in many biological procedures. The transcriptomics data indicated that the phosphorylation of the C-terminal domain of RNA polymerase II might control the cold response genes through the CBF pathway and activate the SOD system to respond to cold stress. The qRT-PCR results showed that the expression of HbCSD1 was significantly downregulated under drought and salt stresses, which might dominate the adaption capability to different stresses. Additionally, salt promoted the expression levels of HbMSD1 and HbMSD2, exhibiting their indispensable role in the salinity reaction. The study results will provide a theoretical basis for deep research on HbSODs in rubber trees. Supplementary Information: The online version contains supplementary material available at 10.1007/s13205-022-03328-7.

Assembly and comparative analysis of the complete mitochondrial genome of three Macadamia species (M. integrifolia, M. ternifolia and M. tetraphylla).

BACKGROUND: Macadamia is a true dicotyledonous plant that thrives in a mild, humid, low wind environment. It is cultivated and traded internationally due to its high-quality nuts thus, has significant development prospects and scientific research value. However, information on the genetic resources of Macadamia spp. remains scanty. RESULTS: The mitochondria (mt) genomes of three economically important Macadamia species, Macadamia integrifolia, M. ternifolia and M. tetraphylla, were assembled through the Illumina sequencing platform. The results showed that each species has 71 genes, including 42 protein-coding genes, 26 tRNAs, and 3 rRNAs. Repeated sequence analysis, RNA editing site prediction, and analysis of genes migrating from chloroplast (cp) to mt were performed in the mt genomes of the three Macadamia species. Phylogenetic analysis based on the mt genome of the three Macadamia species and 35 other species was conducted to reveal the evolution and taxonomic status of Macadamia. Furthermore, the characteristics of the plant mt genome, including genome size and GC content, were studied through comparison with 36 other plant species. The final non-synonymous (Ka) and synonymous (Ks) substitution analysis showed that most of the protein-coding genes in the mt genome underwent negative selections, indicating their importance in the mt genome. CONCLUSION: The findings of this study provide a better understanding of the Macadamia genome and will inform future research on the genus.

The Chromosome-Scale Reference Genome of Macadamia tetraphylla Provides Insights Into Fatty Acid Biosynthesis.

Macadamia is an evergreen tree belonging to the Proteaceae family. The two commercial macadamia species, Macadamia integrifolia and M. tetraphylla, are highly prized for their edible kernels. The M. integrifolia genome was recently sequenced, but the genome of M. tetraphylla has to date not been published, which limits the study of biological research and breeding in this species. This study reports a high-quality genome sequence of M. tetraphylla based on the Oxford Nanopore Technologies technology and high-throughput chromosome conformation capture techniques (Hi-C). An assembly of 750.87 Mb with 51.11 Mb N50 length was generated, close to the 740 and 758 Mb size estimates by flow cytometry and k-mer analysis, respectively. Genome annotation indicated that 61.42% of the genome is composed of repetitive sequences and 34.95% is composed of long terminal repeat retrotransposons. Up to 31,571 protein-coding genes were predicted, of which 92.59% were functionally annotated. The average gene length was 6,055 bp. Comparative genome analysis revealed that the gene families associated with defense response, lipid transport, steroid biosynthesis, triglyceride lipase activity, and fatty acid metabolism are expanded in the M. tetraphylla genome. The distribution of fourfold synonymous third-codon transversion showed a recent whole-genome duplication event in M. tetraphylla. Genomic and transcriptomic analysis identified 187 genes encoding 33 crucial oil biosynthesis enzymes, depicting a comprehensive map of macadamia lipid biosynthesis. Besides, the 55 identified WRKY genes exhibited preferential expression in root as compared to that in other tissues. The genome sequence of M. tetraphylla provides novel insights for breeding novel varieties and genetic improvement of agronomic traits.

Complete mitochondrial genomes of three Mangifera species, their genomic structure and gene transfer from chloroplast genomes.

BACKGROUND: Among the Mangifera species, mango (Mangifera indica) is an important commercial fruit crop. However, very few studies have been conducted on the Mangifera mitochondrial genome. This study reports and compares the newly sequenced mitochondrial genomes of three Mangifera species. RESULTS: Mangifera mitochondrial genomes showed partial similarities in the overall size, genomic structure, and gene content. Specifically, the genomes are circular and contain about 63-69 predicted functional genes, including five ribosomal RNA (rRNA) genes and 24-27 transfer RNA (tRNA) genes. The GC contents of the Mangifera mitochondrial genomes are similar, ranging from 44.42-44.66%. Leucine (Leu) and serine (Ser) are the most frequently used, while tryptophan (Trp) and cysteine (Cys) are the least used amino acids among the protein-coding genes in Mangifera mitochondrial genomes. We also identified 7-10 large chloroplast genomic fragments in the mitochondrial genome, ranging from 1407 to 6142 bp. Additionally, four intact mitochondrial tRNAs genes (tRNA-Cys, tRNA-Trp, tRNA-Pro, and tRNA-Met) and intergenic spacer regions were identified. Phylogenetic analysis based on the common protein-coding genes of most branches provided a high support value. CONCLUSIONS: We sequenced and compared the mitochondrial genomes of three Mangifera species. The results showed that the gene content and the codon usage pattern of Mangifera mitochondrial genomes is similar across various species. Gene transfer from the chloroplast genome to the mitochondrial genome were identified. This study provides valuable information for evolutionary and molecular studies of Mangifera and a basis for further studies on genomic breeding of mango.

Complete chloroplast genome of Baccaurea ramiflora and its phylogenetic analysis.

Baccaurea ramiflora Lour. is a popular tropical fruit tree, mainly grown in Myanmar, India, and other tropical or sub-tropical regions where it is commonly referred to as Myanmar grapes, Burmese grapes, or Latkan, respectively. Besides food, B. ramiflora is a traditional medicinal plant with several pharmaceutical effects. It is also a crucial component of Chinese Dai medicine. Here, the chloroplast genome of B. ramiflora was sequenced, assembled, and annotated. The complete chloroplast genome is 161,093 bp in length with a GC content of 36.71%. Additionally, it comprises a large single-copy region (LSC) of 89,503 bp, a small single-copy region (SSC) of 18,818 bp, and two inverted repeat regions (IRa and IRb) of 26,386 bp. In total, 128 genes were annotated, including 82 protein-coding genes, 37 tRNA genes, 8 rRNA genes, and 1 pseudogene. Phylogenetic analysis revealed that B. ramiflora is closely related to Phyllanthus emblica, Glochidion chodoense, and Phyllanthus amarus. This study provides useful genomic information for future phylogenetic studies of B. ramiflora and Phyllanthaceae family.

The complete chloroplast genome and phylogenetic analysis of Artocarpus champeden.

Artocarpus champeden Spreng. is a popular fruit tree, grown in tropical and subtropical regions. Besides food, A. champeden is also a medicinal plant with various medicinal properties. In this study, A. champeden chloroplast genome was sequenced, assembled, and annotated due to its rich information on species evolution and inter-species genetic relationships. The quadripartite structure of A. champeden complete chloroplast genome is 158,568 bp in length and comprises a large single-copy region (LSC) of 88,076 bp, a small single-copy region (SSC) of 19,028 bp, and two inverted repeat regions (IRa and IRb) of 25,732 bp. A total of 131 genes were annotated, including 85 protein-coding genes, 37 tRNA genes, eight rRNA genes, and one pseudogene. Phylogenetic analysis revealed a close relationship between A. champeden and A. heterophyllus. In addition, the study provides abundant genomic information for future phylogenetic studies of A. champeden and the Moraceae family.

Complete chloroplast genome sequence and phylogenetic analysis of dragon fruit (Selenicereus undatus (Haw.) D.R.Hunt).

Selenicereus undatus (Haw.) D.R.Hunt is a member of the family Cactaceae. The chloroplast genome of S. undatus was sequenced, assembled, and annotated in the present study. The chloroplast genome was 133,326 bp in length, consisting of a typical quadripartite circle: a large single-copy region of 68,256 bp, two inverted repeat regions of 21,677 bp, and a small single copy region of 21,716 bp. A total of 120 predicted genes were identified, and a maximum likelihood was constructed, placing S. undatus as the sister taxon of Lophocereus schottii and Carnegiea gigantea, other members of the family Cactaceae.

Comparative analysis of the complete plastid genomes of Mangifera species and gene transfer between plastid and mitochondrial genomes.

Mango is an important commercial fruit crop belonging to the genus Mangifera. In this study, we reported and compared four newly sequenced plastid genomes of the genus Mangifera, which showed high similarities in overall size (157,780-157,853 bp), genome structure, gene order, and gene content. Three mutation hotspots (trnG-psbZ, psbD-trnT, and ycf4-cemA) were identified as candidate DNA barcodes for Mangifera. These three DNA barcode candidate sequences have high species identification ability. We also identified 12 large fragments that were transferred from the plastid genome to the mitochondrial genome, and found that the similarity was more than 99%. The total size of the transferred fragment was 35,652 bp, accounting for 22.6% of the plastid genome. Fifteen intact chloroplast genes, four tRNAs and numerous partial genes and intergenic spacer regions were identified. There are many of these genes transferred from mitochondria to the chloroplast in other species genomes. Phylogenetic analysis based on whole plastid genome data provided a high support value, and the interspecies relationships within Mangifera were resolved well.

The complete chloroplast genome and phylogenetic analysis of Nephelium lappaceum (rambutan).

Nephelium lappaceum is a popular tropical fruit belonging to the Sapindaceae family. The plant originated in Malaysia and Indonesia and is commonly called rambutan. Because of its refreshing flavor and exotic appearance, rambutan is widely accepted in the World. Due to its significant medicinal properties, the fruit has also been employed in traditional medicine for centuries. The chloroplast genome of rambutan was sequenced, assembled, and annotated in the present study. The chloroplast genome length was 161,356 bp and contained 132 genes, including 87 protein-coding genes, 37 transfer RNA (tRNA) genes, and 8 ribosomal RNA (rRNA) genes. It possessed the typical quadripartite circle structure with a large single-copy region (86,009 bp), a small single-copy region (18,153 bp), and two inverted repeat regions (28,597 bp). A total of 35 SSR markers were found in the chloroplast genome of Nephelium lappaceum, of which 33 were monomer, 1 was dimer and 1 was tetramer. Phylogenetic analysis based on the complete chloroplast genome sequences of 21 plant species showed that rambutan was closely related to Pometia tomentosa. These results provide a foundation for further phylogenetic and evolutionary studies of the Sapindaceae family.

The complete chloroplast genome of Passiflora caerulea, a tropical fruit with a distinctive aroma.

Passiflora caerulea is native to brazil. In recent years, the edible, medicinal, and ornamental value of P. caerulea has stimulated its wide cultivation in Southeast Asian countries, especially China. Because the chloroplast genome is rich with information about the species evolution as well as its genetic relationship to other species, the P. caerulea chloroplast genome was sequenced, assembled, and annotated in this study. The P. caerulea chloroplast genome is 151,362 bp in total with an overall GC content of 37.03%. It has a quadripartite structure, includes a large single-copy region (LSC, 85,623 bp), a small single-copy region (SSC, 13,397 bp), and two inverted repeat regions (IRa and IRb, 26,180 bp combined). There are 131 genes in the P. caerulea chloroplast genome, including 79 protein-coding genes, 37 tRNA genes, 8 rRNA genes, and 7 pseudogenes. Phylogenetic analysis of 29 Passiflora spp. showed that P. caerulea is most closely related to P. edulis. These results provide a considerable foundation for P. caerulea conservation genetics research.

The complete chloroplast genome of Morinda citrifolia (noni).

Morinda citrifolia L. (Rubiaceae), commonly called noni, is a medicinal plant that is often used as botanical dietary supplement. This study is the first to report and characterize the complete chloroplast genome of M. citrifolia. We found that it contains 153,113 bp with a GC content of 38.05%, consisting of two inverted repeat regions (IRs, 25,588 bp), a large single-copy region (LSC, 83,974 bp), and a small single copy (SSC, 17,963 bp) region. One hundred and twenty-five genes were annotated, including 84 protein-coding genes, 33 transfer RNA (tRNA) genes, and 8 ribosomal RNA (rRNA) genes. Phylogenetic analysis showed that M. citrifolia and Gynochthodes officinalis were closely related. Overall, this study provided a wealth of information for a follow-up phylogenetic and evolutionary study of the Gentianales.

The complete chloroplast genome of Hevea camargoana.

Hevea camargoana is a natural latex producing tropical plant and a close relative of H. brasiliensis, the primary commercial source of natural rubber. This study sequenced and analyzed the chloroplast genome of H. camargoana. The circular chloroplast genome of H. camargoana contains 161,291 bp with a GC content of 35.72%. This region contains two inverted repeat regions (26,819 bp), a large single-copy region (89,281 bp), and a small single-copy (18,372 bp) region in the complete chloroplast genome. A total of 134 genes were annotated, including 86 protein-coding genes, 36 transfer RNA genes, 8 ribosomal RNA genes, and 4 pseudogenes. The results showed that H. camargoana and H. brasiliensis were closely related, suggesting that H. camargoana may be used for the future variety improvement of rubber trees.

Complete chloroplast genome of Hevea benthamiana, a SALB-resistant relative wild species of rubber tree.

Hevea benthamiana is a SALB-resistant wild species of H. brasiliensis, the only source of mass production of high quality natural rubber. This study sequenced and analyzed the chloroplast genome of H. benthamiana. The chloroplast genome of H. benthamiana contains 161,124 bp and consists of 51,495 bp of A (31.96%), 52,022 bp of T (32.29%), 28,915 bp of G (17.95%), and 28,692 bp of C (17.81%). The ring-shaped genome includes four regions: a large single-copy region (LSC, 89,110 bp), a small single copy (SSC, 18,376 bp) region, and two inverted repeat regions (IRs, 26,819 bp). A total of 134 genes were annotated, of which 86 encode proteins; four are pseudogenes; 36 are tRNA genes, and eight are rRNA genes. Phylogenetic analyses showed that H. benthamiana is very closely related to H. Brasiliensis, this result indicates that H. benthamiana is highly valuable for the breeding of SALB-resistant varieties of rubber trees.

Complete chloroplast genome of Synsepalum dulcificum D.: a magical plant that modifies sour flavors to sweet.

Synsepalum dulcificum D. belongs to the Sapotaceae family, which is an evergreen shrub native to tropical West Africa. It is a kind of magical plant that has the unique characteristic of modifying sour flavors to sweet. In this study, the chloroplast genome of S. dulcificum was sequenced, assembled, and annotated firstly. Chloroplast genome size of S. dulcificum is 158,463 bp, the circular chloroplast genome consists of four regions: a large single-copy region of 88,256 bp, two inverted repeat regions of 25,958 bp, and a small single-copy region of 18,669 bp, with the GC content of 36.87%. A total of 133 genes were annotated in the S. dulcificum chloroplast genome, of which 88 were protein-coding genes (PCGs), 37 were transfer RNA (tRNA) genes, and eight were ribosomal RNA (rRNA) genes. Phylogenetic analysis showed that Pouteria campechiana was most closely related to S. dulcificum. The study provides important genomic data for further utilization and breeding of S. dulcificum.

The complete chloroplast genome of Annona muricata L.: a tropical fruit with important medicinal properties.

Annona muricata L. (A. muricata) is an important tropical fruit and medicinal plant. It is one of the easily found plants used traditionally in treating cancer. In many tropical countries, especially in Southeast Asia, A. muricata is popular for its edible fruit and medicinal merits. In this study, the complete chloroplast genome of A. muricata was sequenced, assembled, and annotated. The chloroplast genome of A. muricata was found to be a double strand ring structure with the size of 196,038 bp that consists of four regions: a large single-copy region of 75,339 bp, a small single-copy region of 3105 bp, and two inverted repeat regions of 58,797 bp. The GC content of the whole chloroplast genome was 39.92%. It was found that 111 protein-coding genes, one Pseudogene, 38 tRNA genes, and eight rRNA genes were annotated in the chloroplast genome, and the total number of genes was 158. DNA sequences of the chloroplast genomes of 19 species which belonged to three families of Magnoliales order were analyzed and a phylogenetic tree was constructed. The result indicated that A. muricata, Annona cherimola, Uvaria macrophylla, Greenwayodendron suaveolens, and Chieniodendron hainanense had a close phylogenetic relationship. The findings also provided abundant basic data for the genomics study of A. muricata.

Complete chloroplast genome sequence and phylogenetic analysis of Annona reticulata.

Annona reticulata is native to South and Central America which has many phytochemical and pharmacological activities suggesting a wide range of clinical application in lieu of cancer chemotherapy. This study provides abundant genomic data for the genetic relationship study, germplasm resources evaluation and varieties selection of A. reticulata. The complete chloroplast genome of A. reticulata was sequenced, assembled, and annotated in this study. The genome size was 201,906 bp and was divided into four regions: a large single-copy region of 69,650 bp, a small single-copy region of 3,014 bp, and two inverted repeat regions of 64,621 bp. A total number of 164 genes were annotated, including 115 protein-coding genes, one pseudogene, 40 tRNA genes, and eight rRNA genes. In terms of gene function, the 164 genes were divided into four major groups: genes for self-replication, photosynthesis, unknown function, and other genes. A maximum likelihood tree based on the chloroplast genome sequences of 24 plant species was constructed. The result of phylogenetic analysis showed that A. cherimola had the closest relationship with A. reticulate.

The complete chloroplast genome sequence of Manilkara zapota (Linn.) van Royen.

The complete chloroplast genome sequences of Manilkara zapota (Linn.) van Royen in Xishuangbanna, Yunnan province were reported in this study. The length of the sequence was 159,853 bp long with the large single copy (LSC) region of 89,632 bp, the small single copy (SSC) region of 18,747 bp, and two inverted repeat (IR) regions of 27,737 bp. The plastome contained 125 genes, including 84 protein-coding, 8 ribosomal RNA, and 33 transfer RNA genes. The overall GC content was 37.0%. Phylogenetic analysis of 12 representative plastomes within the order Ebenales suggests that M. zapota (Linn.) van Royen is closely related to the species in family Ebenaceae.

The complete chloroplast genome of Theobroma grandiflorum, an important tropical crop.

Theobroma grandiflorum (Willd. ex Spreng.) K. Schum., an economically important tree in the family Malvaceae, is native to the Amazonian region of South America and it is widely cultivated as a tropical crop. Herein, we report the complete chloroplast genome of T. grandiflorum. The size of the complete chloroplast genome of T. grandiflorum is 160,606 bp with 36.88% GC content, which includes a pair of inverted repeat regions (IRs) of 25,496 bp separated by a large single-copy region (LSC) of 89,429 bp and a small single copy (SSC) region of 20,185 bp. A total of 126 genes were annotated, of which 82 were protein-coding genes, 36 were transfer RNA (tRNA) genes, and 8 were ribosomal RNA (rRNA) genes. A maximum-likelihood (ML) analysis supported a close relationship between T. grandiflorum and T. cacao. This study will provide useful information for further phylogenetic and evolutionary analysis of Malvaceae.

Complete chloroplast genome of Helicia nilagirica Bedd. and its phylogenetic analysis.

Helicia nilagirica Bedd. is a medicinal plant. Its fruit is the main raw material from which helicid, a compound that has sedative, hypnotic, analgesic, and other central nervous system inhibitory effects, is extracted. Here, we report and characterize the complete chloroplast genome of H. nilagirica in this study. The complete chloroplast genome of H. nilagirica contains 157,217 bp and consists of four regions, including a large single-copy region (LSC, 85,516 bp), two inverted repeat regions (IRs, 26,700 bp), and a small single copy (SSC, 18,301 bp) region. A total of 132 genes were obtained by annotation, including 88 protein-coding genes, 36 transfer RNA (tRNA) genes, and 8 ribosomal RNA (rRNA) genes. Phylogenetic analysis showed that H. nilagirica is closely related to Macadamia integrifolia, suggesting that H. nilagirica may be used as rootstock or gene donor in macadamia breeding. This study lays a foundation for future phylogenetic and evolutionary studies of Proteaceae.