Complete chloroplast genome sequences of Myristicaceae species with the comparative chloroplast genomics and phylogenetic relationships among them.

BACKGROUND: Myristicaceae was widly distributed from tropical Asia to Oceania, Africa, and tropical America. There are 3 genera and 10 species of Myristicaceae present in China, mainly distributed in the south of Yunnan Province. Most research on this family focuses on fatty acids, medicine, and morphology. Based on the morphology, fatty acid chemotaxonomy, and a few of molecular data, the phylogenetic position of Horsfieldia pandurifolia Hu was controversial. RESULTS: In this study, the chloroplast genomes of two Knema species, Knema globularia (Lam.) Warb. and Knema cinerea (Poir.) Warb., were characterized. Comparing the genome structure of these two species with those of other eight published species, including three Horsfieldia species, four Knema species, and one Myristica species, it was found that the chloroplast genomes of these species were relatively conserved, retaining the same gene order. Through sequence divergence analysis, there were 11 genes and 18 intergenic spacers were subject to positive selection, which can be used to analyze the population genetic structure of this family. Phylogenetic analysis showed that all Knema species were clustered in the same group and formed a sister clade with Myristica species support by both high maximum likelihood bootstrap values and Bayesian posterior probabilities; among Horsfieldia species, Horsfieldia amygdalina (Wall.) Warb., Horsfieldia kingii (Hook.f.) Warb., Horsfieldia hainanensis Merr. and Horsfieldia tetratepala C.Y.Wu. were grouped together, but H. pandurifolia formed a single group and formed a sister clade with genus Myristica and Knema. Through the phylogenetic analysis, we support de Wilde' view that the H. pandurifolia should be separated from Horsfieldia and placed in the genus Endocomia, namely Endocomia macrocoma subsp. prainii (King) W.J.de Wilde. CONCLUSION: The findings of this study provide a novel genetic resources for future research in Myristicaceae and provide a molecular evidence for the taxonomic classification of Myristicaceae.

Transcriptomics integrated with widely targeted metabolomics reveals the cold resistance mechanism in Hevea brasiliensis.

The rubber tree is the primary source of natural rubber and is mainly cultivated in Southeast Asian countries. Low temperature is the major abiotic stress affecting the yield of the rubber tree. Therefore, uncovering the cold resistance mechanism in the rubber tree is necessary. The present study used RNA-sequencing technology and ultra-performance liquid chromatography-tandem mass spectrometry (UPLC-MS/MS) to analyze the transcriptomic and metabolomic changes in two rubber tree clones with different cold resistance capacities (temperature-sensitive Reyan 8-79 and cold-resistant Yunyan 77-4) at 0 h, 2 h, 6 h, and 20 h of exposure to 4°C. Independent analysis of the transcriptome and metabolitome showed that under prolonged low-temperature treatment, Yunyan 77-4 expressed more genes involved in regulating enzyme activity, changing cell permeability, and synthesizing significant metabolites, such as flavonoids and amino acids, than Reyan 8-79. The KEGG annotation and enrichment analysis identified arginine metabolism and biosynthesis of flavonoids as the major pathway associated with cold resistance. Integrated transcriptome and metabolome analysis showed that the increase in the expression of genes modulated flavonoid biosynthesis, arginine biosynthesis, and anthocyanins biosynthesis, resulting in higher levels of metabolites, such as naringenin chalcone, apigenin, dihydroquercetin, cyanidin 3-glucoside, L-arginosuccinate, N-acetyl-ornithine, ornithine, and N-acetyl-glutamate, in Yunyan 77-4 than in Reyan 8-79 after prolonged low-temperature treatment. Phylogenetic analysis identified the genes, such as CHS (gene356) and F3H (gene33147) of flavonoid biosynthesis and NAGS (gene16028, gene33765), ArgC (gene2487), and ASS (gene6161) of arginine biosynthesis were the key genes involved in the cold resistant of rubber tree. Thus, the present study provides novel insights into how rubber clones resist cold and is a valuable reference for cold-resistance breeding.

The complete chloroplast genome sequence of Knema elegans (Myristicaceae).

Knema elegans is a member of Myristicaceae. The K. elegans chloroplast genome is found to be 155,691 bp in length and has a base composition of A (30.02%), G (19.31%), C (19.89%), and T (30.78%). The genome contained two short inverted repeat (IRa and IRb) regions (48,122 bp) which were separated by a large single-copy (LSC) region (86,883 bp) and a small single-copy (SSC) region (20,686 bp). The chloroplast genome has 85 protein-coding genes, 27 transfer RNA (tRNA) genes, and 8 ribosomal RNA (rRNA) genes. Further, complete chloroplast sequence of K. elegans was aligned together with two species of Myristicaceae and five basal angiosperms species for which the complete chloroplast sequence have been reported. This complete chloroplast genome will provide valuable information for the development of DNA markers for future species resource development and phylogenetic analysis of K. elegans.

The complete chloroplast genome sequence of Knema conferta (Myristicaceae).

Knema conferta is a member of Myristicaceae. The K. conferta chloroplast genome is found to be 155,744 bp in length and has a base composition of A (30.02%), G (19.30%), C (19.90%), and T (30.78%). The genome contained two short inverted repeat (IRa and IRb) regions (48,052 bp) which were separated by a large single copy (LSC) region (86,926 bp) and a small single copy (SSC) region (20,770 bp). The genome encoded a total of 128 unigenes, including 89 protein-coding genes, 31 transfer RNA (tRNA) genes, and 8 ribosomal RNA (rRNA) genes. Further, complete chloroplast sequence of K. conferta was aligned together with 2 species of Knema and 5 basal angiosperms species which have reported the complete chloroplast sequence. This complete chloroplast genome will provide valuable information for the development of DNA markers for future species resource development and phylogenetic analysis of K. conferta.

The complete chloroplast genome sequence of Knema linifolia (Myristicaceae).

Knema linifolia is a member of Myristicaceae. The K. linifolia chloroplast genome is found to be 155,754 bp in length and has a base composition of A (30.02%), G (19.30%), C (19.89%), and T (30.79%). The genome contained two short inverted repeat (IRa and IRb) regions (48,080 bp) which were separated by a large single copy (LSC) region (86,991 bp) and a small single copy (SSC) region (20,683 bp). The chloroplast genome has 89 protein-coding genes, 31 transfer RNA (tRNA) genes, and 8 ribosomal RNA (rRNA) genes. Further, complete chloroplast sequence of K. linifolia was aligned together with 2 species of Knema and 5 basal angiosperms species which have reported the complete chloroplast sequence. This complete chloroplast genome will provide valuable information for the development of DNA markers for future species resource development and phylogenetic analysis of K. linifolia.

The Chromosome-Based Rubber Tree Genome Provides New Insights into Spurge Genome Evolution and Rubber Biosynthesis.

The rubber tree, Hevea brasiliensis, produces natural rubber that serves as an essential industrial raw material. Here, we present a high-quality reference genome for a rubber tree cultivar GT1 using single-molecule real-time sequencing (SMRT) and Hi-C technologies to anchor the ∼1.47-Gb genome assembly into 18 pseudochromosomes. The chromosome-based genome analysis enabled us to establish a model of spurge chromosome evolution, since the common paleopolyploid event occurred before the split of Hevea and Manihot. We show recent and rapid bursts of the three Hevea-specific LTR-retrotransposon families during the last 10 million years, leading to the massive expansion by ∼65.88% (∼970 Mbp) of the whole rubber tree genome since the divergence from Manihot. We identify large-scale expansion of genes associated with whole rubber biosynthesis processes, such as basal metabolic processes, ethylene biosynthesis, and the activation of polysaccharide and glycoprotein lectin, which are important properties for latex production. A map of genomic variation between the cultivated and wild rubber trees was obtained, which contains ∼15.7 million high-quality single-nucleotide polymorphisms. We identified hundreds of candidate domestication genes with drastically lowered genomic diversity in the cultivated but not wild rubber trees despite a relatively short domestication history of rubber tree, some of which are involved in rubber biosynthesis. This genome assembly represents key resources for future rubber tree research and breeding, providing novel targets for improving plant biotic and abiotic tolerance and rubber production.

The complete chloroplast genome sequence of Horsfieldia amygdalina (Myristicaceae).

Horsfieldia amygdalina is a member of Myristicaceae. The H. amygdalina chloroplast genome is found to be 155,683 bp in length and has a base composition of A (29.99%), G (19.32%), C (19.92%), and T (30.77%). The genome contained two short inverted repeat (IRa and IRb) regions (37,754 bp) which were separated by a large single copy (LSC) region (86,931 bp) and a small single copy (SSC) region (30,998 bp). The genome encodes 121 unique genes, including 86 protein-coding genes, 27 transfer RNA (tRNA) genes, and 8 ribosomal RNA (rRNA) genes. Further, complete chloroplast sequence of H. amygdalina was aligned together with Horsfieldia pandurifolia, Myristica yunnanensis and other Magnoliales and basal angiosperms species which have reported the complete chloroplast sequence. This complete chloroplast genome will provide valuable information for the development of DNA markers for future species resource development and phylogenetic analysis of H. amygdalina.

The complete chloroplast genome sequence of Horsfieldia kingii (Myristicaceae).

Horsfieldia kingii is a member of Myristicaceae. The H. kingii chloroplast genome is found to be 155,655 bp in length and has a base composition of A (30.03%), G (19.52%), C (19.72%), and T (30.73%). The genome contained two short inverted repeat (IRa and IRb) regions (48,052 bp) which were separated by a large single copy (LSC) region (86,912 bp) and a small single copy (SSC) region (20,691 bp). The genome encodes 123 unique genes, including 85 protein-coding genes, 27 transfer RNA (tRNA) genes, and 8 ribosomal RNA (rRNA) genes. Further, complete chloroplast sequence of H. kingii was aligned together with other 2 species of Myristicaceae and other 5 basal angiosperms species which have reported the complete chloroplast sequence. This complete chloroplast genome will provide valuable information for the development of DNA markers for future species resource development and phylogenetic analysis of H. kingii.

The complete chloroplast genome sequence of Knema furfuracea (Myristicaceae).

Knema furfuracea is a member of Myristicaceae. The K. furfuracea chloroplast genome is found to be 154,527 bp in length and has a base composition of A (29.99%), G (19.31%), C (19.92%), and T (30.78%). The genome contained two short inverted repeat (IRa and IRb) regions (48,110 bp) which were separated by a large single copy (LSC) region (86,188 bp) and a small single copy (SSC) region (20,229 bp). The chloroplast genome has 87 protein-coding genes, 27 transfer RNA (tRNA) genes, and 8 ribosomal RNA (rRNA) genes. Further, complete chloroplast sequence of K. furfuracea was aligned together with two species of Myristicaceae and five basal angiosperms species which have reported the complete chloroplast sequence. This complete chloroplast genome will provide valuable information for the development of DNA markers for future species resource development and phylogenetic analysis of K. furfuracea.

Chloroplast genome of tropical and sub-tropical fruit tree Clausena lansium (Rutaceae).

The Clausena lansium, originally native to the southern part of China and has a long history of cultivation, is a tree member of the family Rutaceae. Chloroplast genome sequences play a significant role in the development of molecular markers in plant phylogenetic and population genetic studies. In this study, we report the complete chloroplast genome sequence of C. lansium for the first time (accession number of MH047377). The chloroplast genome is 159,284 bp long and includes 113 genes. It's LSC, SSC, and IR regions are 88,634, 18,896, and 25,877 bp long, respectively. Phylogenetic tree analysis exhibited that C. lansium was clustered with other Rutaceae species with high bootstrap values.

The complete chloroplast genome of tropical and sub-tropical fruit tree Lucuma nervosa (Sapotaceae).

The Lucuma nervosa, native to Western Ghats of India, Malaysia and south-eastern Asia, is a tree member of the mulberry family (Sapotaceae). Chloroplast genome sequences play an significant role in the development of molecular markers in plant phylogenetic and population genetic studies. In this study, we report the complete chloroplast genome sequence of L. nervosa for the first time. The chloroplast genome is 157,920 bp long and includes 113 genes. Its LSC, SSC, and IR regions are 88,123, 18,861, and 25,468 bp long, respectively. Phylogenetic tree analysis exhibited that L. nervosa was clustered with other Sapotaceae species with high bootstrap values.