Plastome phylogenomics and biogeography of the subfam. Polygonoideae (Polygonaceae)

The complete chloroplast genome and phylogenetic analysis of Persicaria jucunda (Meisn.) Migo (Polygonaceae)

Persicaria jucunda is a plant distributed at meadow or wetland. Our study reports the complete chloroplast genome. The chloroplast genome of P. jucunda is a typical tetrameric structure with a total length of 159,843 bp, containing a large single-copy (LSC) region of 84,350 bp, a small single-copy (SSC) region of 13,151 bp, and two inverted repeat regions (IRs) of 31,171 bp. The total GC content was 38.2%, 36.5% for the LSC region, 33.2% for the SSC region, and 41.5% for the IR region. The P. jucunda chloroplast genome contains 128 genes, including 83 protein-coding genes, 37 tRNA genes, and eight rRNA genes. Phylogenetic analysis based on 36 chloroplast genomes showed similarity to P. foliosa and P. kawagoeana among the species analyzed. The chloroplast genome provides a valuable genetic resource for phylogenetic studies.

Comparative Analyses of the Complete Mitogenomes of Two Oxyria Species (Polygonaceae) Provide Insights into Understanding the Mitogenome Evolution Within the Family

Oxyria (Polygonaceae) is a small genus only comprising two species, Oxyria digyna and O. sinensis. Both species have well-documented usage in Chinese herbal medicine. We sequenced and assembled the complete mitogenomes of these two species and conducted a comparative analysis of the mitogenomes within Polygonaceae. Both O. digyna and O. sinensis displayed distinctive multi-branched conformations, consisting of one linear and one circular molecule. These two species shared similar gene compositions and exhibited distinct codon preferences, with mononucleotides as the most abundant type of simple sequence repeats. In the mitogenome of O. sinensis, a pair of long forward repeat sequences can mediate the division of molecule 1 into two sub-genomic circular molecules. Homologous sequence analysis revealed the occurrence of gene transfer between the chloroplast and mitochondrial genomes within Oxyria species. Additionally, a substantial number of homologous collinear blocks with varied arrangements were observed across different Polygonaceae species. Phylogenetic analysis suggested that mitogenome genes can serve as reliable markers for constructing phylogenetic relationships within Polygonaceae. Comparative analysis of eight species revealed Polygonaceae mitogenomes exhibited variability in gene presence, and most protein-coding genes (PCGs) have undergone negative selection. Overall, our study provided a comprehensive overview of the structural, functional, and evolutionary characteristics of the Polygonaceae mitogenomes.

Characteristics and phylogenetic analysis of the complete chloroplast genome of Mesembryanthemum cordifolium L. F. (Aizoaceae)

Mesembryanthemum cordifolium, a perennial plant with crassulacean acid metabolism (CAM) in the Aizoaceae family, has significant ornamental and medicinal values. In this study, we reported the first complete chloroplast genome sequence of this species. The total genome size was 153,734 bp in length, including a large single-copy (LSC) region of 85,692 bp, a small single-copy (SSC) region of 18,212 bp, and a pair of inverted repeat (IR) regions of 24,915 bp by each. The overall GC content of the M. cordifolium chloroplast genome was 37.08%. The genome encodes 131 genes, comprising 87 protein-coding genes (PCGs), 36 transfer RNA genes (tRNAs), and eight ribosomal RNA genes (rRNAs). Phylogenetic analysis shows this species was relatively close to M. crystallinum. This chloroplast genome sequence will be valuable for species discrimination and for understanding phylogenetic relationships within the genus Mesembryanthemum.

The complete annotated plastome sequences of six genera in the tropical woody Polygonaceae

BACKGROUND

The Polygonaceae is a family well-known for its weeds, and edible plants, Fagopyrum (buckwheat) and Rheum (rhubarb), which are primarily herbaceous and temperate in distribution. Yet, the family also contains a number of lineages that are principally distributed in the tropics and subtropics. Notably, these lineages are woody, unlike their temperate relatives. To date, full-genome sequencing has focused on the temperate and herbaceous taxa. In an effort to increase breadth of genetic knowledge of the Polygonaceae, we here present six fully assembled and annotated chloroplast genomes from six of the tropical, woody genera: Coccoloba rugosa (a narrow and endangered Puerto Rican endemic), Gymnopodium floribundum, Neomillspaughia emarginata, Podopterus mexicanus, Ruprechtia coriacea, and Triplaris cumingiana.

RESULTS

These assemblies represent the first publicly-available assembled and annotated plastomes for the genera Podopterus, Gymnopodium, and Neomillspaughia, and the first assembled and annotated plastomes for the species Coccoloba rugosa, Ruprechtia coriacea, and Triplaris cumingiana. We found the assembled chloroplast genomes to be above the median size of Polygonaceae plastomes, but otherwise exhibit features typical of the family. The features of greatest sequence variation are found among the ndh genes and in the small single copy (SSC) region of the plastome. The inverted repeats show high GC content and little sequence variation across genera. When placed in a phylogenetic context, our sequences were resolved within the Eriogonoideae.

CONCLUSIONS

These six plastomes from among the tropical woody Polygonaceae appear typical within the family. The plastome assembly of Ruprechtia coriacea presented here calls into question the sequence identity of a previously published plastome assembly of R. albida.

A chromosome-level genome reveals genome evolution and molecular basis of anthraquinone biosynthesis in Rheum palmatum

BACKGROUND

Rhubarb is one of common traditional Chinese medicine with a diverse array of therapeutic efficacies. Despite its widespread use, molecular research into rhubarb remains limited, constraining our comprehension of the geoherbalism.

RESULTS

We assembled the genome of Rheum palmatum L., one of the source plants of rhubarb, to elucidate its genome evolution and unpack the biosynthetic pathways of its bioactive compounds using a combination of PacBio HiFi, Oxford Nanopore, Illumina, and Hi-C scaffolding approaches. Around 2.8 Gb genome was obtained after assembly with more than 99.9% sequences anchored to 11 pseudochromosomes (scaffold N50 = 259.19 Mb). Transposable elements (TE) with a continuous expansion of long terminal repeat retrotransposons (LTRs) is predominant in genome size, contributing to the genome expansion of R. palmatum. Totally 30,480 genes were predicted to be protein-coding genes with 473 significantly expanded gene families enriched in diverse pathways associated with high-altitude adaptation for this species. Two successive rounds of whole genome duplication event (WGD) shared by Fagopyrum tataricum and R. palmatum were confirmed. We also identified 54 genes involved in anthraquinone biosynthesis and other 97 genes entangled in flavonoid biosynthesis. Notably, RpALS emerged as a compelling candidate gene for the octaketide biosynthesis after the key residual screening.

CONCLUSION

Overall, our findings offer not only an enhanced understanding of this remarkable medicinal plant but also pave the way for future innovations in its genetic breeding, molecular design, and functional genomic studies.

The complete chloroplast genome of the medicinally important plant Plumbago zeylanica L. (plumbaginaceae) and phylogenetic analysis

Plumbago zeylanica L. 1753 is a medicinally-important herb in family Plumbaginaceae. In this study, we assembled and reported the complete chloroplast genome of P. zeylanica. The plastome of P. zeylanica was 169,178 bp, including a large single-copy region of 92,135 bp, a small single-copy region (SSC) of 13,455 bp and a pair of inverted repeat regions (IRs) of 31,794 bp. It contained 124 genes, including 79 protein-coding genes, 37 tRNA genes and eight rRNA genes. Phylogenetic analysis showed that P. zeylanica formed a close relationship with P. auriculata in Plumbago. The first complete chloroplast genome report of P. zeylanica providing an opportunity to explore the genetic diversity, and would be also helpful in the species identification and conservation.