Plastid genome evolution of a monophyletic group in the subtribe Lauriineae (Laureae, Lauraceae)

Central Asia revealed as a key area in evolution of Eremurus (Asphodelaceae)

Eremurus was described at the beginning of the 19th century. However, due to limited sampling and the small number of gene markers to date, its phylogeny and evolution are largely unknown. In this study, we analyzed plastomes from 27 species belonging to 2 subgenera and 3 sections of Eremurus, which are found in Central Asia (its center of diversity) and China. We also analyzed nuclear DNA ITS of 33 species, encompassing all subgenera and sections of the genus in Central Asia, southwest Asia and China. Our findings revealed that the genus was monophyletic, although both subgenera Eremurus and Henningia were found to be paraphyletic. Both plastome and nrDNA-based phylogenetic trees had three clades that did not reflect the current taxonomy of the genus. Our biogeographical and time-calibrated trees suggest that Eremurus originated in the ancient Tethyan area in the second half of the Eocene. Diversification of Eremurus occurred from the early Oligocene to the late Miocene. Paratethys Sea retreat and several orogenetic events, such as the progressive uplift of the Qinghai-Tibet Plateau and surrounding mountain belts (Altai, Pamir, Tian Shan), caused serious topographic and climate (aridification) changes in Central Asia that may have triggered a split of clades and speciation. In this transformed Central Asia, speciation proceeded rapidly driven mainly by vicariance caused by numerous mountain chains and specialization to a variety of climatic, topographic and soil conditions that exist in this region.

Comparative chloroplast genomes of Argentina species: genome evolution and phylogenomic implications

The genus Argentina Hill belongs to the tribe Potentilleae Sweet and contains approximately 75 species predominantly distributed in the Sino-Himalayan region and the Malesian archipelago. So far we have less knowledge on the phylogenetic relationships within Argentina owing to limited sampling of Argentina taxa or gene fragments in previous studies. Moreover, to date there is no phylogenetic study on Argentina from the perspective of comparative chloroplast (cp) genomics. Here we performed comparative genomic analyses on the cp genomes of 39 accessions representing 18 taxa of Argentina. The Argentina cp genomes presented the typical quadripartite structure, with the sizes ranging from 155 096 bp to 157 166 bp. The 39 Argentina cp genomes contained a set of 112 unique genes, comprising four ribosomal RNA (rRNA) genes, 30 transfer RNA (tRNA) genes, as well as 78 protein-coding genes (PCGs). The cp genome organization, gene content and order in Argentina were highly conserved, but some visible divergences were present in IR/SC boundary regions. Ten regions (trnH-GUG-psbA, trnG-GCC-trnfM-CAU, trnD-GUC-trnY-GUA, rpl32-trnL-UAG, atpH-atpI, rps16-trnQ-UUG, trnS-GCU-trnG-UCC, ndhF-rpl32, trnR-UCU-atpA, and accD-psaI) were identified as excellent candidate DNA markers for future studies on species identification, population genetics and phylogeny of Argentina. Our results indicated that Argentina is monophyletic. In the current sampling, the A. smithiana - A. anserina clade was sister to the remainder of Argentina. Our results corroborated the previous taxonomic treatments to transfer A. phanerophlebia and A. micropetala from the genus Sibbaldia L. to Argentina. Our results showed close relationships among A. stenophylla, A. microphylla, A. taliensis, and A. tatsienluensis, congruent with previous studies based on the morphology of these species. Twenty-six genes (rps3, rps15, rps16, rps19, rpl16, rpl20, rpl22, rpoA, rpoB, rpoC1, rpoC2, atpA, atpF, psbB, psbF, ndhA, ndhB, ndhC, ndhD, ndhF, rbcL, accD, ccsA, matK, ycf1, ycf2) were with sites under positive selection, and adaptive evolution of these genes might have played crucial roles in Argentina species adaptation to the harsh mountain environment. This study will facilitate future work on taxonomy, phylogenetics, and adaptive evolution of Argentina.

Intraspecific differentiation of Lindera obtusiloba as revealed by comparative plastomic and evolutionary analyses

Lindera obtusiloba Blume is the northernmost tree species in the family Lauraceae, and it is a key species in understanding the evolutionary history of this family. The species of L. obtusiloba in East Asia has diverged into the Northern and Southern populations, which are geographically separated by an arid belt. Though the morphological differences between populations have been observed and well documented, intraspecific variations at the plastomic level have not been systematically investigated to date. Here, ten chloroplast genomes of L. obtusiloba individuals were sequenced and analyzed along with three publicly available plastomes. Comparative plastomic analysis suggests that both the Northern and the Southern populations share similar overall structure, gene order, and GC content in their plastomes although the size of the plasome and the level of intraspecific variability do vary between the two populations. The Northern have relatively larger plastomes while the Southern population possesses higher intraspecific variability, which could be attributed to the complexity of the geological environments in the South. Phylogenomic analyses also support the split of the Northern and Southern clades among L. obtusiloba individuals. However, there is no obvious species boundary between var. obtusiloba and var. heterophylla in the Southern population, indicating that gene flow could still occur between these two varieties, and this could be used as a good example of reticulate evolution. It is also found that a few photosynthesis-related genes are under positive selection, which is mainly related to the geological and environmental differences between the Northern and the Southern regions. Our results provide a reference for phylogenetic analysis within species and suggest that phylogenomic analyses with a sufficient number of nuclear and chloroplast genomic target loci from widely distributed individuals could provide a deeper understanding of the population evolution of the widespread species.

Comparative Analysis of Chloroplast Genomes of "Tiantai Wu-Yao" (Lindera aggregata) and Taxa of the Same Genus and Different Genera

Lindera aggregata is a species of the Lauraceae family, which has important medicinal, economic and ornamental values. In this study, we sequenced, assembled and annotated the chloroplast genome of L. aggregata and reannotated and corrected eight unverified annotations in the same genus. The chloroplast genomes taxa from Lindera and from different genera of Lauraceae were compared and analyzed, and their phylogenetic relationship and divergence time were speculated. All the 36 chloroplast genomes had typical quadripartite structures that ranged from 150,749 to 154,736 bp in total length. These genomes encoded 111-112 unique genes, including 78-79 protein-coding genes, 29-30 tRNA and 4 rRNA. Furthermore, there were 78-97 SSRs loci in these genomes, in which mononucleotide repeats were the most abundant; there were 24-49 interspersed repeats, and forward repeat types were the most frequent. The codon bias patterns of all species tended to use codons ending with A or U. Five and six highly variable regions were identified within genus and between genera, respectively, and three common regions (ycf1, ndhF-rpl32 and rpl32-trnL) were identified, which can be used as important DNA markers for phylogeny and species identification. According to the evaluation of the Ka/Ks ratio, most of the genes were under purifying selection, and only 10 genes were under positive selection. Finally, through the construction of the evolutionary tree of 39 chloroplast genomes, the phylogenetic relationship of Lauraceae was clarified and the evolutionary relationship of Lindera was revealed. The species of genus Lindera experienced rapid adaptive radiation from Miocene to Pleistocene. The results provided valuable insights for the study of chloroplast genomes in the Lauraceae family, especially in the genus Lindera.

Comparative analysis and characterization of the chloroplast genome of Krascheninnikovia ceratoides (Amarathaceae): a xerophytic semi-shrub exhibiting drought resistance and high-quality traits

BACKGROUND

Krascheninnikovia ceratoides, a perennial halophytic semi-shrub belonging to the genus Krascheninnikovia (Amarathaceae), possesses noteworthy ecological, nutritional, and economic relevance. This species is primarily distributed across arid, semi-arid, and saline-alkaline regions of the Eurasian continent, encompassing Inner Mongolia, Xinjiang, Qinghai, Gansu, Ningxia, and Tibet.

RESULTS

We reported the comprehensive chloroplast (cp) genome of K. ceratoides, characterized by a circular conformation spanning 151,968 bp with a GC content of 36.60%. The cp genome encompassed a large single copy (LSC, 84,029 bp), a small single copy (SSC, 19,043 bp), and a pair of inverted repeats (IRs) regions (24,448 bp each). This genome harbored 128 genes and encompassed 150 simple sequence repeats (SSRs). Through comparative analyses involving cp genomes from other Cyclolobeae (Amarathaceae) taxa, we observed that the K. ceratoides cp genome exhibited high conservation, with minor divergence events in protein-coding genes (PCGs) accD, matK, ndhF, ndhK, ycf1, and ycf2. Phylogenetic reconstructions delineated K. ceratoides as the sister taxon to Atriplex, Chenopodium, Dysphania, and Suaeda, thus constituting a robust clade. Intriguingly, nucleotide substitution ratios (Ka/Ks) between K. ceratoides and Dysphania species for ycf1 and ycf2 genes surpassed 1.0, indicating the presence of positive selection pressure on these loci.

CONCLUSIONS

The findings of this study augment the genomic repository for the Amarathaceae family and furnish crucial molecular instruments for subsequent investigations into the ecological adaptation mechanisms of K. ceratoides within desert ecosystems.

Comparative analyses of eight complete plastid genomes of two hemiparasitic Cassytha vines in the family Lauraceae

Cassytha is the sole genus of hemiparasitic vines (ca. 20 spp.) belonging to the Cassytheae tribe of the Lauraceae family. It is extensively distributed in tropical and subtropical regions. In this study, we determined the complete plastid genome sequences of C. filiformis and C. larsenii, which do not possess the typical quadripartite structure. The length of C. filiformis plastomes ranged from 114,215 to 114,618 bp, whereas that of C. larsenii plastomes ranged from 114,900 to 114,988 bp. Comparative genomic analysis revealed 1,013 mutation sites, four large intragenomic deletions, and five highly variable regions in the eight plastome sequences. Phylogenetic analyses based on 61 complete plastomes of Laurales species, 19 ITS sequences, and trnK barcodes from 91 individuals of Cassytha spp. confirmed a non-basal group comprising individuals of C. filiformis, C. larsenii, and C. pubescens in the family Lauraceae and proposed a sister relationship between C. filiformis and C. larsenii. Further morphological comparisons indicated that the presence or absence of hairs on the haustoria and the shape or size of fruits were useful traits for differentiating C. filiformis and C. larsenii.

Comparative and phylogenetic analysis of complete chloroplast genomes from seven Neocinnamomum taxa (Lauraceae)

The genus Neocinnamomum is considered to be one of the most enigmatic groups in Lauraceae, mainly distributed in tropical and subtropical regions of Southeast Asia. The genus contains valuable oilseed and medicinal tree species. However, there are few studies on the genus Neocinnamomum at present, and its interspecific relationship is still unclear. In order to explore the genetic structure and evolutionary characteristics of the Neocinnamomum chloroplast genome and to resolve the species relationships within the genus, comparative genomic and phylogenetic analyses were performed on the whole chloroplast genome sequences of 51 samples representing seven Neocinnamomum taxa. The whole Neocinnamomum chloroplast genome size ranged from 150,753-150,956 bp, with a GC content of 38.8%-38.9%. A total of 128 genes were annotated within the Neocinnamomum chloroplast genome, including 84 protein coding genes, 8 rRNA genes, and 36 tRNA genes. Between 71-82 SSRs were detected, among which A/T base repeats were the most common. The chloroplast genome contained a total of 31 preferred codons. Three highly variable regions, trnN-GUU-ndhF, petA-psbJ, and ccsA-ndhD, were identified with Pi values > 0.004. Based on the whole chloroplast genome phylogenetic tree, the phylogenetic relationships among the seven Neocinnamomum taxa were determined. N. delavayi and N. fargesii were the most closely related species, and N. lecomtei was identified as the most basal taxon. In this study, the characteristics and sequence variation of the chloroplast genomes of seven Neocinnamomum taxa were revealed, and the genetic relationship among the species was clarified. The results of this study will provide a reference for subsequent molecular marker development and phylogenetic research of Neocinnamomum.

Molecular phylogeny and inflorescence evolution of Prunus (Rosaceae) based on RAD-seq and genome skimming analyses

Prunus is an economically important genus widely distributed in the temperate Northern Hemisphere. Previous studies on the genus using a variety of loci yielded conflicting phylogenetic hypotheses. Here, we generated nuclear reduced representation sequencing data and plastid genomes for 36 Prunus individuals and two outgroups. Both nuclear and plastome data recovered a well-resolved phylogeny. The species were divided into three main clades corresponding to their inflorescence types, - the racemose group, the solitary-flower group and the corymbose group - with the latter two sister to one another. Prunus was inferred to have diversified initially in the Late Cretaceous around 67.32 million years ago. The diversification of the three major clades began between the Paleocene and Miocene, suggesting that paleoclimatic events were an important driving force for Prunus diversification. Ancestral state reconstructions revealed that the most recent common ancestor of Prunus had racemose inflorescences, and the solitary-flower and corymb inflorescence types were derived by reduction of flower number and suppression of the rachis, respectively. We also tested the hybrid origin hypothesis of the racemose group proposed in previous studies. Prunus has undergone extensive hybridization events, although it is difficult to identify conclusively specific instances of hybridization when using SNP data, especially deep in the phylogeny. Our study provides well-resolved nuclear and plastid phylogenies of Prunus, reveals substantial cytonuclear discord at shallow scales, and sheds new light on inflorescence evolution in this economically important lineage.

Plastome structure, phylogenomics, and divergence times of tribe Cinnamomeae (Lauraceae)

BACKGROUND

Tribe Cinnamomeae is a species-rich and ecologically important group in tropical and subtropical forests. Previous studies explored its phylogenetic relationships and historical biogeography using limited loci, which might result in biased molecular dating due to insufficient parsimony-informative sites. Thus, 15 plastomes were newly sequenced and combined with published plastomes to study plastome structural variations, gene evolution, phylogenetic relationships, and divergence times of this tribe.

RESULTS

Among the 15 newly generated plastomes, 14 ranged from 152,551 bp to 152,847 bp, and the remaining one (Cinnamomum chartophyllum XTBGLQM0164) was 158,657 bp. The inverted repeat (IR) regions of XTBGLQM0164 contained complete ycf2, trnI^CAU, rpl32, and rpl2. Four hypervariable plastid loci (ycf1, ycf2, ndhF-rpl32-trnL^UAG, and petA-psbJ) were identified as candidate DNA barcodes. Divergence times based on a few loci were primarily determined by prior age constraints rather than by DNA data. In contrast, molecular dating using complete plastid protein-coding genes (PCGs) was determined by DNA data rather than by prior age constraints. Dating analyses using PCGs showed that Cinnamomum sect. Camphora diverged from C. sect. Cinnamomum in the late Oligocene (27.47 Ma).

CONCLUSIONS

This study reports the first case of drastic IR expansion in tribe Cinnamomeae, and indicates that plastomes have sufficient parsimony-informative sites for molecular dating. Besides, the dating analyses provide preliminary insights into the divergence time within tribe Cinnamomeae and can facilitate future studies on its historical biogeography.

Complete plastid genome of Litsea honghoensis Liou 1933, an endangered evergreen species in China

Litsea honghoensis Liou is an endangered tree endemic to south China. In this study, the first complete plastid genome of L. honghoensis was presented, which had a length of 152,605 base pairs (bp) with a GC content of 39.20%. The genome consisted of a large single-copy (LSC) region of 93,560 bp, a small single-copy (SSC) region of 18,905 bp, and two inverted repeat regions (IRa and IRb) of 20,070 bp. There were 125 genes in the plastid genome, including 81 protein-coding genes, 36 transfer RNA (tRNA) genes, and eight ribosomal RNA (rRNA) genes. Phylogenomic analysis based on 52 complete plastomes of Laureae in the family Lauraceae supports the close relationships among L. honghoensis, Lindera communis, Lindera nacusua, Lindera angustifolia, and Lindera glauca.