Complete chloroplast genome sequences of two endangered Phoebe (Lauraceae) species

Comparative genomics analysis of endangered wild Egyptian Moringa peregrina (Forssk.) Fiori plastome, with implications for the evolution of Brassicales order

Moringa is a mono-genus belonging to the Moringaceae family, which includes 13 species. Among them, Moringa peregrina is plant species native to the Arabian Peninsula, Southern Sinai in Egypt, and the Horn of Africa, and comprehensive studies on its nutritional, industrial, and medicinal values have been performed. Herein, we sequenced and analyzed the initial complete chloroplast genome of Moringa peregrina. Concurrently, we analyzed the new chloroplast genome along with 25 chloroplast genomes related to species representing eight families in the Brassicales order. The results indicate that the plastome sequence of M. peregrina consists of 131 genes, with an average GC content of 39.23%. There is a disparity in the IR regions of the 26 species ranging from 25,804 to 31,477 bp. Plastome structural variations generated 20 hotspot regions that could be considered prospective DNA barcode locations in the Brassicales order. Tandem repeats and SSR structures are reported as significant evidence of structural variations among the 26 tested specimens. Furthermore, selective pressure analysis was performed to estimate the substitution rate within the Moringaceae family, which revealing that the ndhA and accD genes are under positive selective pressure. The phylogenetic analysis of the Brassicales order produced an accurate monophyletic annotation cluster of the Moringaceae and Capparaceae species, offering unambiguous identification without overlapping groups between M. oleifera and M. peregrina, which are genetically strongly associated. Divergence time estimation suggests that the two Moringa species recently diversified, 0.467 Ma. Our findings highlight the first complete plastome of the Egyptian wild-type of M. peregrina, which can be used for determining plastome phylogenetic relationships and systematic evolution history within studies on the Moringaceae family.

Paclobutrazol Promotes Root Development of Difficult-to-Root Plants by Coordinating Auxin and Abscisic Acid Signaling Pathways in Phoebe bournei

Phoebe bournei is a rare and endangered plant endemic to China with higher-value uses in essential oil and structural wood production. Its seedlings are prone to death because of its undeveloped system. Paclobutrazol (PBZ) can improve root growth and development in certain plants, but its concentration effect and molecular mechanism remain unclear. Here, we studied the physiological and molecular mechanisms by which PBZ regulates root growth under different treatments. We found that, with moderate concentration treatment (MT), PBZ significantly increased the total root length (69.90%), root surface area (56.35%), and lateral root number (47.17%). IAA content was the highest at MT and was 3.83, 1.86, and 2.47 times greater than the control, low, and high-concentration treatments. In comparison, ABA content was the lowest and reduced by 63.89%, 30.84%, and 44.79%, respectively. The number of upregulated differentially expressed genes (DEGs) induced at MT was more than that of down-regulated DEGs, which enriched 8022 DEGs in response to PBZ treatments. WGCNA showed that PBZ-responsive genes were significantly correlated with plant hormone content and involved in plant hormone signal transduction and MAPK signal pathway-plant pathways, which controls root growth. The hub genes are observably associated with auxin, abscisic acid syntheses, and signaling pathways, such as PINs, ABCBs, TARs, ARFs, LBDs, and PYLs. We constructed a model which showed PBZ treatments mediated the antagonism interaction of IAA and ABA to regulate the root growth in P. bournei. Our result provides new insights and molecular strategies for solving rare plants' root growth problems.

Comparative chloroplast genome analyses of diverse Phoebe (Lauraceae) species endemic to China provide insight into their phylogeographical origin

The genus Phoebe (Lauraceae) includes about 90 evergreen tree species that are an ideal source of timber. Habitat destruction and deforestation have resulted in most of them being endemic to China. The accurate identification of endangered Phoebe species in China is necessary for their conservation. Chloroplast genome sequences can play an important role in species identification. In this study, comparative chloroplast genome analyses were conducted on diverse Phoebe species that are primarily distributed in China. Despite the conserved nature of chloroplast genomes, we detected some highly divergent intergenic regions (petA-psbE, ndhF-rpl32, and psbM-trnD-GUC) as well as three highly divergent genes (rbcL, ycf1, and ycf2) that have potential applications in phylogenetics and evolutionary analysis. The phylogenetic analysis indicated that various Phoebe species in China were divided into three clades. The complete chloroplast genome was better suited for phylogenetic analysis of Phoebe species. In addition, based on the phylogeographical analysis of Phoebe species in China, we inferred that the Phoebe species in China first originated in Yunnan and then spread to other southern areas of the Yangtze River. The results of this research will add to existing case studies on the phylogenetic analysis of Phoebe species and have the potential to contribute to the conservation of Phoebe species that are in danger of extinction.

The chloroplast genome of black pepper (Piper nigrum L.) and its comparative analysis with related Piper species

Piper nigrum, also known as black pepper, is an economically and ecologically important crop of the genus Piper. It has been titled as the king of spices due to its wide consumption throughout the world. In the present investigation, the chloroplast genome of P. nigrum has been assembled from a whole genome sequence by integrating the short and long reads generated through Illumina and PacBio platforms, respectively. The chloroplast genome was observed to be 161,522 bp in size, having a quadripartite structure with a large single copy (LSC) region of 89,153 bp and a small single copy (SSC) region of 18,255 bp separated by a copy of inverted repeats (IRs), each 27,057 bp in length. Taking into consideration all the duplicated genes, a total of 131 genes were observed, which included 81 protein-coding genes, 37 tRNAs, 4 rRNAs, and 1 pseudogene. Individually, the LSC region consisted of 83 genes, the SSC region had 13 genes, and 18 genes were present in each IR region. Additionally, 216 SSRs were detected and 11 of these were validated through amplification in 12 species of Piper. The features of the chloroplast genome have been compared with those of the genus Piper. Our results provide useful insights into evolutionary and molecular studies of black pepper which will contribute to its further genetic improvement and breeding.

The Complete Chloroplast Genome of Hypoestes forskaolii (Vahl) R.Br: Insights into Comparative and Phylogenetic Analyses within the Tribe Justiceae

Hypoestes forskaolii is one of the most important species of the family Acanthaceae, known for its high economic and medicinal importance. It is well distributed in the Arab region as well as on the African continent. Previous studies on ethnomedicine have reported that H. forskaolii has an anti-parasitic effect as well as antimalarial and anthelmintic activities. Previous studies mainly focused on the ethnomedicinal properties, hence, there is no information on the genomic architecture and phylogenetic positions of the species within the tribe Justiceae. The tribe Justicieae is the most taxonomically difficult taxon in Acanthoideae due to its unresolved infratribal classification. Therefore, by sequencing the complete chloroplast genome (cp genome) of H. forskaolii, we explored the evolutionary patterns of the cp genome and reconstructed the phylogeny of Justiceae. The cp genome is quadripartite and circular in structure and has a length of 151,142 bp. There are 130 genes (86 coding for protein, 36 coding for tRNA and 8 coding for rRNA) present in the plastome. Analyses of long repeats showed only three types of repeats: forward, palindromic and reverse were present in the genome. Microsatellites analysis revealed 134 microsatellites in the cp genome with mononucleotides having the highest frequency. Comparative analyses within Justiceae showed that genomes structure and gene contents were highly conserved but there is a slight distinction in the location of the genes in the inverted repeat and single copy junctions. Additionally, it was discovered that the cp genome includes variable hotspots that can be utilized as DNA barcodes and tools for determining evolutionary relationships in the Justiceae. These regions include: atpH-atpI, trnK-rps16, atpB-rbcL, trnT-trnL, psbI-trnS, matK, trnH-psbA, and ndhD. The Bayesian inference phylogenetic tree showed that H. forskaolii is a sister to the Dicliptra clade and belongs to Diclipterinae. The result also confirms the polyphyly of Justicia and inclusion of Diclipterinae within justicioid. This research has revealed the phylogenetic position of H. forskaolii and also reported the resources that can be used for evolutionary and phylogenetic studies of the species and the Justicieae.

A comparative analysis of complete chloroplast genomes of seven Ocotea species (Lauraceae) confirms low sequence divergence within the Ocotea complex

The genus Ocotea (Lauraceae) includes about 450 species, of which about 90% are Neotropical, while the rest is from Macaronesia, Africa and Madagascar. In this study we present the first complete chloroplast genome sequences of seven Ocotea species, six Neotropical and one from Macaronesia. Genome sizes range from 152,630 (O. porosa) to 152,685 bp (O. aciphylla). All seven plastomes contain a total of 131 (114 unique) genes, among which 87 (80 unique) encode proteins. The order of genes (if present) is the same in all Lauraceae examined so far. Two hypervariable loci were found in the LSC region (psbA-trnH, ycf2), three in the SSC region (ycf1, ndhH, trnL(UAG)-ndhF). The pairwise cp genomic alignment between the taxa showed that the LSC and SSC regions are more variable compared to the IR regions. The protein coding regions comprise 25,503–25,520 codons in the Ocotea plastomes examined. The most frequent amino acids encoded in the plastomes were leucine, isoleucine, and serine. SSRs were found to be more frequent in the two dioecious Neotropical Ocotea species than in the four bisexual species and the gynodioecious species examined (87 vs. 75–84 SSRs). A preliminary phylogenetic analysis based on 69 complete plastomes of Lauraceae species shows the seven Ocotea species as sister group to Cinnamomum sensu lato. Sequence divergence among the Ocotea species appears to be much lower than among species of the most closely related, likewise species-rich genera Cinnamomum, Lindera and Litsea.

Comparative Analysis of Chloroplast Genomes of Four Medicinal Capparaceae Species: Genome Structures, Phylogenetic Relationships and Adaptive Evolution

This study presents for the first time the complete chloroplast genomes of four medicinal species in the Capparaceae family belonging to two different genera, Cadaba and Maerua (i.e., C. farinosa, C. glandulosa, M. crassifolia and M. oblongifolia), to investigate their evolutionary process and to infer their phylogenetic positions. The four species are considered important medicinal plants, and are used in the treatment of many diseases. In the genus Cadaba, the chloroplast genome ranges from 156,481 bp to 156,560 bp, while that of Maerua ranges from 155,685 bp to 155,436 bp. The chloroplast genome of C. farinosa, M. crassifolia and M. oblongifolia contains 138 genes, while that of C. glandulosa contains 137 genes, comprising 81 protein-coding genes, 31 tRNA genes and 4 rRNA genes. Out of the total genes, 116–117 are unique, while the remaining 19 are replicated in inverted repeat regions. The psbG gene, which encodes for subunit K of NADH dehydrogenase, is absent in C. glandulosa. A total of 249 microsatellites were found in the chloroplast genome of C. farinosa, 251 in C. glandulosa, 227 in M. crassifolia and 233 in M. oblongifolia, the majority of which are mononucleotides A/T found in the intergenic spacer. Comparative analysis revealed variable hotspot regions (atpF, rpoC2, rps19 and ycf1), which can be used as molecular markers for species authentication and as regions for inferring phylogenetic relationships among them, as well as for evolutionary studies. The monophyly of Capparaceae and other families under Brassicales, as well as the phylogenetic positions of the studied species, are highly supported by all the relationships in the phylogenetic tree. The cp genomes reported in this study will provide resources for studying the genetic diversity of Capparaceae, as well as resolving phylogenetic relationships within the family.

Seven Complete Chloroplast Genomes from Symplocos: Genome Organization and Comparative Analysis

In the present study, chloroplast genome sequences of four species of Symplocos (S. chinensis for. pilosa, S. prunifolia, S. coreana, and S. tanakana) from South Korea were obtained by Ion Torrent sequencing and compared with the sequences of three previously reported Symplocos chloroplast genomes from different species. The length of the Symplocos chloroplast genome ranged from 156,961 to 157,365 bp. Overall, 132 genes including 87 functional genes, 37 tRNA genes, and eight rRNA genes were identified in all Symplocos chloroplast genomes. The gene order and contents were highly similar across the seven species. The coding regions were more conserved than the non-coding regions, and the large single-copy and small single-copy regions were less conserved than the inverted repeat regions. We identified five new hotspot regions (rbcL, ycf4, psaJ, rpl22, and ycf1) that can be used as barcodes or species-specific Symplocos molecular markers. These four novel chloroplast genomes provide basic information on the plastid genome of Symplocos and enable better taxonomic characterization of this genus.

Comparative analysis and phylogenetic investigation of Hong Kong Ilex chloroplast genomes

Ilex is a monogeneric plant group (containing approximately 600 species) in the Aquifoliaceae family and one of the most commonly used medicinal herbs. However, its taxonomy and phylogenetic relationships at the species level are debatable. Herein, we obtained the complete chloroplast genomes of all 19 Ilex types that are native to Hong Kong. The genomes are conserved in structure, gene content and arrangement. The chloroplast genomes range in size from 157,119 bp in Ilex graciliflora to 158,020 bp in Ilex kwangtungensis. All these genomes contain 125 genes, of which 88 are protein-coding and 37 are tRNA genes. Four highly varied sequences (rps16-trnQ, rpl32-trnL, ndhD-psaC and ycf1) were found. The number of repeats in the Ilex genomes is mostly conserved, but the number of repeating motifs varies. The phylogenetic relationship among the 19 Ilex genomes, together with eight other available genomes in other studies, was investigated. Most of the species could be correctly assigned to the section or even series level, consistent with previous taxonomy, except Ilex rotunda var. microcarpa, Ilex asprella var. tapuensis and Ilex chapaensis. These species were reclassified; I. rotunda was placed in the section Micrococca, while the other two were grouped with the section Pseudoaquifolium. These studies provide a better understanding of Ilex phylogeny and refine its classification.

EST-SSR marker development based on transcriptome sequencing and genetic analyses of Phoebe bournei (Lauraceae)

High-throughput sequencing of the Phoebe bournei transcriptome was performed, and novel SSR markers were identified. A total of 73,518 nonredundant unigenes were assembled and annotated by sequence similarity searching in diverse public databases. A total of 40,853 SSRs were identified from 73,518 unigenes. Twenty-three pairs of polymorphic EST-SSR markers were selected from 98 markers and used for genetic analyses in 75 individuals from three P. bournei populations. The 23 pairs of markers could detect abundant genetic information from the samples (PIC = 0.769), and cross-species amplification was successfully performed in other related species. Three populations had high level of genetic diversity (He = 0.658 in average), of which the population YS from Jiangxi province had the most abundant genetic diversity (He = 0.722). The results of genetic structure analyses showed that the population YS from Jiangxi province had obvious genetic differences from the other two populations, and the genetic information of the population SX from Fujian province was related to that of the population LC from Guangdong province and the population YS. The transcriptomic resources and EST-SSR markers are valuable tools not only for the ecological conservation of P. bournei but also for phylogenetic studies.

Complete Chloroplast Genome of Abutilon fruticosum: Genome Structure, Comparative and Phylogenetic Analysis

Abutilon fruticosum is one of the endemic plants with high medicinal and economic value in Saudi Arabia and belongs to the family Malvaceae. However, the plastome sequence and phylogenetic position have not been reported until this study. In this research, the complete chloroplast genome of A. fruticosum was sequenced and assembled, and comparative and phylogenetic analyses within the Malvaceae family were conducted. The chloroplast genome (cp genome) has a circular and quadripartite structure with a total length of 160,357 bp and contains 114 unique genes (80 protein-coding genes, 30 tRNA genes and 4 rRNA genes). The repeat analyses indicate that all the types of repeats (palindromic, complement, forward and reverse) were present in the genome, with palindromic occurring more frequently. A total number of 212 microsatellites were identified in the plastome, of which the majority are mononucleotides. Comparative analyses with other species of Malvaceae indicate a high level of resemblance in gene content and structural organization and a significant level of variation in the position of genes in single copy and inverted repeat borders. The analyses also reveal variable hotspots in the genomes that can serve as barcodes and tools for inferring phylogenetic relationships in the family: the regions include trnH-psbA, trnK-rps16, psbI-trnS, atpH-atpI, trnT-trnL, matK, ycf1 and ndhH. Phylogenetic analysis indicates that A. fruticosum is closely related to Althaea officinalis, which disagrees with the previous systematic position of the species. This study provides insights into the systematic position of A. fruticosum and valuable resources for further phylogenetic and evolutionary studies of the species and the Malvaceae family to resolve ambiguous issues within the taxa.

The Phoebe genome sheds light on the evolution of magnoliids

Lauraceae includes the genus Phoebe, and the family is linked to the evolution of magnoliids. We sequenced the genome of Phoebe bournei Nanmu. The assembled genome size was 989.19 Mb, with a contig N50 value of 2.05 Mb. A total of 28,198 protein-coding genes were annotated in P. bournei. Whole-genome duplication (WGD) analysis showed that Lauraceae has experienced two WGD events; the older WGD event occurred just before the divergence of Lauraceae and Magnoliales, and the more recent WGD was shared by all lineages of Lauraceae. The phylogenetic tree showed that magnoliids form a sister clade to monocots and eudicots. We also identified 63 MADS-box genes, including AGL12-like genes that may be related to the regulation of P. bournei roots and FIN219-like genes encoding GH3 proteins, which are involved in photomorphogenesis. SAUR50-like genes involved in light signal-mediated pedicel or stem development were also identified. Four ATMYB46- and three PtrEPSP-homologous genes related to lignin biosynthesis were identified. These genes may be associated with the formation of straight trunks in P. bournei. Overall, the P. bournei reference genome provides insight into the origin, evolution, and diversification of Phoebe and other magnoliids.

Plastome phylogenomics, systematics, and divergence time estimation of the Beilschmiedia group (Lauraceae)

Intergeneric relationships of the Beilschmiedia group (Lauraceae) remain unresolved, hindering our understanding of their classification and evolutionary diversification. To remedy this, we sequenced and assembled complete plastid genomes (plastomes) from 25 species representing five genera spanning most major clades of Beilschmiedia and close relatives. Our inferred phylogeny is robust and includes two major clades. The first includes a monophyletic Endiandra nested within a paraphyletic Australasian Beilschmiedia group. The second includes (i) a subclade of African Beilschmiedia plus Malagasy Potameia, (ii) a subclade of Asian species including Syndiclis and Sinopora, (iii) the lone Neotropical species B. immersinervis, (iv) a subclade of core Asian Beilschmiedia, sister to the Neotropical species B. brenesii, and v) two Asian species including B. turbinata and B. glauca. The rampant non-monophyly of Beilschmiedia we identify necessitates a major taxonomic realignment of the genus, including but not limited to the mergers of Brassiodendron and Sinopora into the genera Endiandra and Syndiclis, respectively. Along these lines, the high degree of continental, clade-wide endemism we identify suggests that geographical distribution may be a good proxy for delineating taxa within this group. Our molecular divergence time estimates indicate that stem Beilschmiedia group members date to the Early Eocene (~50 Ma); their crown age dates to the Eocene-Oligocene boundary (~34 Ma). These findings contradict older estimates of the group and support mounting evidence that the origin and diversification of many pantropical angiosperm clades are not easily attributed to strict western Gondwanan vicariance. Finally, our study highlights the phylogenetic utility of plastomes in Lauraceace, and lays a solid foundation for future phylogenomic and biogeographic investigations within the family.

Comparative analysis of the complete chloroplast genome sequences of six species of Pulsatilla Miller, Ranunculaceae

BACKGROUND

Baitouweng is a traditional Chinese medicine with a long history of different applications. Although referred to as a single medicine, Baitouweng is actually comprised of many closely related species. It is therefore critically important to identify the different species that are utilized in these medicinal applications. Knowledge about their phylogenetic relationships can be derived from their chloroplast genomes and may provide additional insights into development of molecular markers.

METHODS

Genomic DNA was extracted from six species of Pulsatilla and then sequenced on an Illumina HiSeq 4000. Sequences were assembled into contigs by SOAPdenovo 2.04, aligned to the reference genome using BLAST, and then manually corrected. Genome annotation was performed by the online DOGMA tool. General characteristics of the cp genomes of the six species were analyzed and compared with closely related species. Additionally, phylogenetic trees were constructed, based on single nucleotide polymorphisms (SNPs) and 51 shared protein-coding gene sequences in the cp genome among all 31 species via maximum likelihood.

RESULTS

The size of cp genomes of P. chinensis (Bge.) Regel, P. chinensis (Bge.) Regel var. kissii (Mandl) S. H. Li et Y. H. Huang, P. cernua (Thunb.) Bercht. et Opiz f. plumbea J. X. Ji et Y. T. zhao, P. dahurica (Fisch.) Spreng, P. turczaninovii Kryl. et Serg, and P. cernua (Thunb.) Bercht. et Opiz. were 163,851 bp, 163,756 bp, 162,481 bp, 162,450 bp, 162,795 bp, and 162,924 bp, respectively. Each species included two inverted repeat regions, a small single-copy region, and a large single-copy region. A total of 134 genes were annotated, including 90 protein-coding genes, 36 tRNAs, and eight rRNAs across all species. In simple sequence repeat analysis, only P. dahurica was found to contain hexanucleotide repeats. A total of 26, 39, 32, 37, 32 and 43 large repeat sequences were identified in the genic regions of the six Pulsatilla species. Nucleotide diversity analysis revealed that the rpl36 gene and ccsA-ndhD region have the highest Pi value. In addition, two phylogenetic trees of the cp genomes were constructed, which laced all Pulsatilla species into one branch within Ranunculaceae.

CONCLUSIONS

We identified and analyzed the cp genome features of six species of P. Miller, with implications for species identification and phylogenetic analysis.

Comparison of the Complete Eragrostis pilosa Chloroplast Genome with Its Relatives in Eragrostideae (Chloridoideae; Poaceae)

Eragrostis of the tribe Eragrostideae is a taxonomically complex genus, because of its polyploid nature and the presence of similar morphological characters among its species. However, the relationship between these morphologically indistinguishable species at the genomic level has not yet been investigated. Here, we report the complete chloroplast genome of E. pilosa and compare its genome structures, gene contents, simple sequence repeats (SSRs), sequence divergence, codon usage bias, and Kimura 2-parameter (K2P) interspecific genetic distances with those of other Eragrostideae species. The E. pilosa chloroplast genome was 134,815 bp in length and contained 132 genes and four regions, including a large single-copy region (80,100 bp), a small single-copy region (12,661 bp), and a pair of inverted repeats (21,027 bp). The average nucleotide diversity between E. pilosa and E. tef was estimated to be 0.011, and 0.01689 among all species. The minimum and maximum K2P interspecific genetic distance values were identified in psaA (0.007) and matK (0.029), respectively. Of 45 SSRs, eight were shared with E. tef, all of which were in the LSC region. Phylogenetic analysis resolved the monophyly of the sampled Eragrostis species and confirmed the close relationship between E. pilosa and E. tef. This study provides useful chlorophyll genomic information for further species identification and phylogenetic reconstruction of Eragrostis species.

Characterization of 20 complete plastomes from the tribe Laureae (Lauraceae) and distribution of small inversions

Lindera Thunb. (Lauraceae) consists of approximately 100 species, mainly distributed in the temperate and tropical regions of East Asia. In this study, we report 20 new, complete plastome sequences including 17 Lindera species and three related species, Actinodaphne lancifolia, Litsea japonica and Sassafras tzumu. The complete plastomes of Lindera range from 152,502 bp (L. neesiana) to 154,314 bp (L. erythrocarpa) in length. Eleven small inversion (SI) sites are documented among the plastomes. Six of the 11 SI sites are newly reported and they locate in rpoB-trnC, psbC-trnS, petA-psbJ, rpoA and ycf2 regions. The distribution patterns of SIs are useful for species identification. An average of 83 simple sequence repeats (SSRs) were detected in each plastome. The mono-SSRs accounted for 72.7% of total SSRs, followed by di- (12.4%), tetra- (9.4%), tri- (4.2%), and penta-SSRs (1.3%). Of these SSRs, 64.6% were distributed in an intergenic spacer (IGS) region. In addition, 79.8% of the SSRs are located in a large single copy (LSC) region. In contrast, almost no SSRs are distributed in inverted repeat (IR) regions. The SSR loci are useful to identifying species but the phylogenetic value is low because the majority of them show autapomorphic status or highly homoplastic characteristics. The nucleotide diversity (Pi) values also indicated the conserved nature of the IR region compared to LSC and small single copy (SSC) regions. Five spacer regions with high Pi values, trnH-psbA, petA-psbJ and ndhF-rpl32, rpl32-trnL and Ψycf1-ndhF, have a potential use for the molecular identification study of Lindera and related species. Lindera species form a paraphyletic group in the plastome tree because of the inclusion of related genera such as Actinodaphne, Laurus, Litsea and Neolitsea. A former member of tribe Laureae, Sassafras, forms a clade with the tribe Cinnamomeae. The SIs do not affect the phylogenetic relationship of Laureae. This result indicated that ancient plastome captures may have contribute to the mixed intergeneric relationship of Laureae. Alternatively, the result may indicate that the morphological characters defined the genera of Lauraceae originated for several times.

Plastome sequences help to improve the systematic position of trinerved Lindera species in the family Lauraceae

Lindera is a genus (c. 100 spp.) of trees belonging to the “core Laureae” group in the family Lauraceae. It is often confused with Litsea, and the systematics of the genus is unclear. Here, total 10 complete plastomes from nine trinerved Lindera species and another species Lindera obtusiloba (sect. Palminerviae Meissn.) were sequenced. Nine highly variable regions, trnH-GUG/psbA, psbM/trnD-GUC, petA/psbL, ndhF, trnL-UAG/ndhD, and ycf1, were identified among the 10 Lindera species. In addition, a total of 1,836 mutation events including six micro-inversions, 156 indels, and 1,674 substitutions, were also summarized. Comparing our sequences with other available plastomes in the “core Laureae,” we put forward that six hypervariable loci, trnH-GUG/psbA, ndhF, ndhF/rpl32, trl32/trnL-UAG, ndhD, and ycf1, could potentially be used as plastid barcode candidates for species identification. Further phylogenetic analyses were conducted using 49 complete Lauraceae plastomes. The results supported a close relationship among trinerved Lindera species and suggested an improved trinerved group comprising species of trinerved Lindera species and Iteadaphne caudate.

Comparison of Four Complete Chloroplast Genomes of Medicinal and Ornamental Meconopsis Species: Genome Organization and Species Discrimination

High-throughput sequencing of chloroplast genomes has been used to gain insight into the evolutionary relationships of plant species. In this study, we sequenced the complete chloroplast genomes of four species in the Meconopsis genus: M. racemosa, M. integrifolia (Maxim.) Franch, M. horridula and M. punicea. These plants grow in the wild and are recognized as having important medicinal and ornamental applications. The sequencing results showed that the size of the Meconopsis chloroplast genome ranges from 151864 to 153816 bp. A total of 127 genes comprising 90 protein-coding genes, 37 tRNA genes and 8 rRNA genes were observed in all four chloroplast genomes. Comparative analysis of the four chloroplast genomes revealed five hotspot regions (matK, rpoC2, petA, ndhF, and ycf1), which could potentially be used as unique molecular markers for species identification. In addition, the ycf1 gene may also be used as an effective molecular marker to distinguish Papaveraceae and determine the evolutionary relationships among plant species in the Papaveraceae family. Futhermore, these four genomes can provide valuable genetic information for other related studies.

Chloroplast genome analysis of box-ironbark Eucalyptus

Eucalyptus L'Hérit. (Myrtaceae) is a taxonomically complex and highly speciose genus that dominates much of Australia's woody vegetation. However, very little information is available about the molecular biology and chloroplast diversity of certain groups, such as Eucalyptus section Adnataria, which is found in many woodland habitats of eastern Australia. We report four new complete chloroplast genomes of Eucalyptus, including three genomes from species previously lacking any chloroplast reference sequences. Plastomes of E. albens, E. conica, E. crebra and E. melliodora assembled using a de novo approach were shown to be largely identical to each other, and similar in size and structure to previously published chloroplast genomes from Eucalyptus. A total of 132 genes (114 single-copy genes and 18 duplicated genes in the IR regions) were identified, and shown to be highly conserved in terms of gene order, content and organization. Slightly higher divergence in the intergenic spacers was identified through comparative genomic analyses. Chloroplast sequences of 35 additional individuals representing 12 species were assembled using a reference guided approach. Rates of nucleotide substitution varied among the protein coding genes, with 17 genes under possible positive selection, and 29 invariant genes. Phylogenetic analysis of either the whole reconstructed plastome sequences or the individual genes revealed extreme discordance with expected species boundaries or higher-level relationships. Plastome relationships were better predicted by geography than by nuclear DNA or taxonomic relationships, suggesting a substantial influence of gene flow over and above the effects of incomplete lineage sorting. These results provide resources for future research and valuable insights into the prevalence of interspecific gene flow among Eucalyptus species.

The Complete Chloroplast Genomes of Echinacanthus Species (Acanthaceae): Phylogenetic Relationships, Adaptive Evolution, and Screening of Molecular Markers

Among the four species of Echinacanthus (Acanthaceae), one distributed in the West Himalayan region and three restricted to the Sino-Vietnamese karst region. Because of its ecological significance, molecular markers are necessary for proper assessment of its genetic diversity and phylogenetic relationships. Herein, the complete chloroplast genomes of four Echinacanthus species were determined for the first time. The results indicated that all the chloroplast genomes were mapped as a circular structure and each genomes included 113 unique genes, of which 80 were protein-coding, 29 were tRNAs, and 4 were rRNAs. However, the four cp genomes ranged from 151,333 to 152,672 bp in length. Comparison of the four cp genomes showed that the divergence level was greater between geographic groups. We also analyzed IR expansion or contraction in the four cp genomes and the fifth type of the large single copy/inverted repeat region in Lamiales was suggested. Furthermore, based on the analyses of comparison and nucleotide variability, six most divergent sequences (rrn16, ycf1, ndhA, rps16-trnQ-UUG, trnS-GCU-trnG-UCC, and psaA-ycf3) were identified. A total of 37-45 simple sequence repeats were discovered in the four species and 22 SSRs were identified as candidate effective molecular markers for detecting interspecies polymorphisms. These SSRs and hotspot regions could be used as potential molecular markers for future study. Phylogenetic analysis based on Bayesian and parsimony methods did not support the monophyly of Echinacanthus. The phylogenetic relationships among the four species were clearly resolved and the results supported the recognition of the Sino-Vietnamese Echinacanthus species as a new genus. Based on the protein sequence evolution analysis, 12 genes (rpl14, rpl16, rps4, rps15, rps18, rps19, psbK, psbN, ndhC, ndhJ, rpoB, and infA) were detected under positive selection in branch of Sino-Vietnamese Echinacanthus species. These genes will lead to understanding the adaptation of Echinacanthus species to karst environment. The study will help to resolve the phylogenetic relationship and understand the adaptive evolution of Echinacanthus. It will also provide genomic resources and potential markers suitable for future species identification and speciation studies of the genus.