Genomes of autotetraploid wild and cultivated Ziziphus mauritiana reveal polyploid evolution and crop domestication.

Indian jujube (Ziziphus mauritiana) holds a prominent position in the global fruit and pharmaceutical markets. Here, we report the assemblies of haplotype-resolved, telomere-to-telomere genomes of autotetraploid wild and cultivated Indian jujube plants using a two-stage assembly strategy. The generation of these genomes permitted in-depth investigations into the divergence and evolutionary history of this important fruit crop. Using a graph-based pan-genome constructed from eight monoploid genomes, we identified structural variation (SV)-FST hotspots and SV hotspots. Gap-free genomes provide a means to obtain a global view of centromere structures. We identified presence-absence variation-related genes in four monoploid genomes (cI, cIII, wI, and wIII) and resequencing populations. We also present the population structure and domestication trajectory of the Indian jujube based on the resequencing of 73 wild and cultivated accessions. Metabolomic and transcriptomic analyses of mature fruits of wild and cultivated accessions unveiled the genetic basis underlying loss of fruit astringency during domestication of Indian jujube. This study reveals mechanisms underlying the divergence, evolution, and domestication of the autotetraploid Indian jujube and provides rich and reliable genetic resources for future research.

SubPhaser: a robust allopolyploid subgenome phasing method based on subgenome-specific k-mers.

With advanced sequencing technology, dozens of complex polyploid plant genomes have been characterized. However, for many polyploid species, their diploid ancestors are unknown or extinct, making it impossible to unravel the subgenomes and genome evolution directly. We developed a novel subgenome-phasing algorithm, SubPhaser, specifically designed for a neoallopolyploid or a homoploid hybrid. SubPhaser first searches for the subgenome-specific sequence (k-mer), then assigns homoeologous chromosomes into subgenomes, and further provides tools to annotate and investigate specific sequences. SubPhaser works well on neoallopolyploids and homoploid hybrids containing subgenome-specific sequences like wheat, but fails on autopolyploids lacking subgenome-specific sequences like alfalfa, indicating that SubPhaser can phase neoallopolyploid/homoploid hybrids with high accuracy, sensitivity and performance. This highly accurate, highly sensitive, ancestral data free chromosome phasing algorithm, SubPhaser, offers significant application value for subgenome phasing in neoallopolyploids and homoploid hybrids, and for the subsequent exploration of genome evolution and related genetic/epigenetic mechanisms.

Comparative Transcriptome Analysis Provides Insights into Response of Ulva compressa to Fluctuating Salinity Conditions.

Ulva compressa, a green tide-forming species, can adapt to hypo-salinity conditions, such as estuaries and brackish lakes. To understand the underlying molecular mechanisms of hypo-salinity stress tolerance, transcriptome-wide gene expression profiles in U. compressa were created using digital gene expression profiles. The RNA-seq data were analyzed based on the comparison of differently expressed genes involved in specific pathways under hypo-salinity and recovery conditions. The up-regulation of genes in photosynthesis and glycolysis pathways may contribute to the recovery of photosynthesis and energy metabolism, which could provide sufficient energy for the tolerance under long-term hyposaline stress. Multiple strategies, such as ion transportation and osmolytes metabolism, were performed to maintain the osmotic homeostasis. Additionally, several long noncoding RNA were differently expressed during the stress, which could play important roles in the osmotolerance. Our work will serve as an essential foundation for the understanding of the tolerance mechanism of U. compressa under the fluctuating salinity conditions.

HomBlocks: A multiple-alignment construction pipeline for organelle phylogenomics based on locally collinear block searching.

Organelle phylogenomic analysis requires precisely constructed multi-gene alignment matrices concatenated by pre-aligned single gene datasets. For non-bioinformaticians, it can take days to weeks to manually create high-quality multi-gene alignments comprising tens or hundreds of homologous genes. Here, we describe a new and highly efficient pipeline, HomBlocks, which uses a homologous block searching method to construct multiple sequence alignment. This approach can automatically recognize locally collinear blocks among organelle genomes and excavate phylogenetically informative regions to construct multiple sequence alignment in a few hours. In addition, HomBlocks supports organelle genomes without annotation and makes adjustment to different taxon datasets, thereby enabling the inclusion of as many common genes as possible. Topology comparison of trees built by conventional multi-gene and HomBlocks alignments implemented in different taxon categories shows that the same efficiency can be achieved by HomBlocks as when using the traditional method. The availability of Homblocks makes organelle phylogenetic analyses more accessible to non-bioinformaticians, thereby promising to lead to a better understanding of phylogenic relationships at an organelle genome level. AVAILABILITY AND IMPLEMENTATION: HomBlocks is implemented in Perl and is supported by Unix-like operative systems, including Linux and macOS. The Perl source code is freely available for download from https://github.com/fenghen360/HomBlocks.git, and documentation and tutorials are available at https://github.com/fenghen360/HomBlocks. CONTACT: yxmao@ouc.edu.cn or fenghen360@126.com.

Transcriptome-wide identification of optimal reference genes for expression analysis of Pyropia yezoensis responses to abiotic stress.

BACKGROUND: Pyropia yezoensis, a marine red alga, is an ideal research model for studying the mechanisms of abiotic stress tolerance in intertidal seaweed. Real-time quantitative polymerase chain reaction (RT-qPCR) is the most commonly used method to analyze gene expression levels. To accurately quantify gene expression, selection and validation of stable reference genes is required. RESULTS: We used transcriptome profiling data from different abiotic stress treatments to identify six genes with relatively stable expression levels: MAP, ATPase, CGS1, PPK, DPE2, and FHP. These six genes and three conventional reference genes, UBC, EF1-α, and eif4A, were chosen as candidates for optimal reference gene selection. Five common statistical approaches (geNorm, ΔCt method, NormFinder, BestKeeper, and ReFinder) were used to identify the stability of each reference gene. Our results show that: MAP, UBC, and FHP are stably expressed in all analyzed conditions; CGS1 and UBC are stably expressed under conditions of dehydration stress; and MAP, UBC, and CGS1 are stably expressed under conditions of temperature stress. CONCLUSION: We have identified appropriate reference genes for RT-qPCR in P. yezoensis under different abiotic stress conditions which will facilitate studies of gene expression under these conditions.

Characterization of the Complete Chloroplast Genomes of Buddleja colvilei and B. sessilifolia: Implications for the Taxonomy of Buddleja L.

Buddleja colvilei Hook.f. & Thomson (Scrophulariaceae) is a threatened alpine plant with a distribution throughout the Himalayas, also used as an ornamental plant. The name Buddleja sessilifolia B.S. Sun ex S.Y. Pao was assigned in 1983 to a plant distributed throughout the Gaoligong Mountains, but the name was later placed in synonymy with B. colvilei in the Flora of China. In this study we sequenced the complete chloroplast (cp) genomes of two individuals of B. colvilei and three individuals of B. sessilifolia from across the range. Both molecular and morphological analysis support the revision of B. sessilifolia. The phylogenetic analysis constructed with the whole cp genomes, the large single-copy regions (LSC), small single-copy regions (SSC), inverted repeat (IR) and the nuclear genes 18S/ITS1/5.8S/ITS2/28S all supported B. sessilifolia as a distinct species. Additionally, coalescence-based species delimitation methods (bGMYC, bPTP) using the whole chloroplast datasets also supported B. sessilifolia as a distinct species. The results suggest that the B. sessilifolia lineage was early diverging among the Asian Buddleja species. Overall gene contents were similar and gene arrangements were found to be highly conserved in the two species, however, fixed differences were found between the two species. A total of 474 single nucleotide polymorphisms (SNPs) were identified between the two species. The Principal Coordinate Analysis of the morphological characters resolved two groups and supported B. sessilifolia as a distinct species. Discrimination of B. colvilei and B. sessilifolia using morphological characters and the redescription of B. sessilifolia are detailed here.

The complete chloroplast genome of Gracilariopsis lemaneiformis (Rhodophyta) gives new insight into the evolution of family Gracilariaceae.

The complete chloroplast genome of Gracilariopsis lemaneiformis was recovered from a Next Generation Sequencing data set. Without quadripartite structure, this chloroplast genome (183,013 bp, 27.40% GC content) contains 202 protein-coding genes, 34 tRNA genes, 3 rRNA genes, and 1 tmRNA gene. Synteny analysis showed plasmid incorporation regions in chloroplast genomes of three species of family Gracilariaceae and in Grateloupia taiwanensis of family Halymeniaceae. Combined with reported red algal plasmid sequences in nuclear and mitochondrial genomes, we postulated that red algal plasmids may have played an important role in ancient horizontal gene transfer among nuclear, chloroplast, and mitochondrial genomes. Substitution rate analysis showed that purifying selective forces maintaining stability of protein-coding genes of nine red algal chloroplast genomes over long periods must be strong and that the forces acting on gene groups and single genes of nine red algal chloroplast genomes were similar and consistent. The divergence of Gp. lemaneiformis occurred ~447.98 million years ago (Mya), close to the divergence time of genus Pyropia and Porphyra (443.62 Mya).

Comparative transcriptome profiling of Pyropia yezoensis (Ueda) M.S. Hwang & H.G. Choi in response to temperature stresses.

BACKGROUND: Pyropia yezoensis is a model organism often used to investigate the mechanisms underlying stress tolerance in intertidal zones. The digital gene expression (DGE) approach was used to characterize a genome-wide comparative analysis of differentially expressed genes (DEGs) that influence the physiological, developmental or biochemical processes in samples subjected to 4 treatments: high-temperature stress (HT), chilling stress (CS), freezing stress (FS) and normal temperature (NT). RESULTS: Equal amounts of total RNAs collected from 8 samples (two biological replicates per treatment) were sequenced using the Illumina/Solexa platform. Compared with NT, a total of 2202, 1334 and 592 differentially expressed unigenes were detected in HT, CS and FS respectively. Clustering analysis suggested P. yezoensis acclimates to low and high-temperature stress condition using different mechanisms: In heat stress, the unigenes related to replication and repair of DNA and protein processing in endoplasmic reticulum were active; however at low temperature stresses, unigenes related to carbohydrate metabolism and energy metabolism were active. Analysis of gene differential expression showed that four categories of DEGs functioning as temperature sensors were found, including heat shock proteins, H2A, histone deacetylase complex and transcription factors. Heat stress caused chloroplast genes down-regulated and unigenes encoding metacaspases up-regulated, which is an important regulator of PCD. Cold stress caused an increase in the expression of FAD to improve the proportion of polyunsaturated fatty acids. An up-regulated unigene encoding farnesyl pyrophosphate synthase was found in cold stress, indicating that the plant hormone ABA also played an important role in responding to temperature stress in P. yezoensis. CONCLUSION: The variation of amount of unigenes and different gene expression pattern under different temperature stresses indicated the complicated and diverse regulation mechanism in response to temperature stress in P. yezoensis. Several common metabolism pathways were found both in P. yezoensis and in higher plants, such as FAD in low-temperature stress and HSP in heat stress. Meanwhile, many chloroplast genes and unigene related to the synthesis of abscisic acid were detected, revealing its unique temperature-regulation mechanism in this intertidal species. This sequencing dataset and analysis may serve as a valuable resource to study the mechanisms involved in abiotic stress tolerance in intertidal seaweeds.

ORPA: a fast and efficient phylogenetic analysis method for constructing genome-wide alignments of organelle genomes.

Creating a multi-gene alignment matrix for phylogenetic analysis using organelle genomes involves aligning single-gene datasets manually, a process that can be time-consuming and prone to errors. The HomBlocks pipeline has been created to eliminate the inaccuracies arising from manual operations. The processing of a large number of sequences, however, remains a time-consuming task. To conquer this challenge, we develop a speedy and efficient method called Organelle Genomes for Phylogenetic Analysis (ORPA). ORPA can quickly generate multiple sequence alignments for whole-genome comparisons by parsing the result files of NCBI BLAST, completing the task just in 1 min. With increasing data volume, the efficiency of ORPA is even more pronounced, over 300 times faster than HomBlocks in aligning 60 high-plant chloroplast genomes. The phylogenetic tree outputs from ORPA are equivalent to HomBlocks, indicating its outstanding efficiency. Due to its speed and accuracy, ORPA can identify species-level evolutionary conflicts, providing valuable insights into evolutionary cognition.

The high-quality genome of Grona styracifolia uncovers the genomic mechanism of high levels of schaftoside, a promising drug candidate for treatment of COVID-19.

Recent study has evidenced that traditional Chinese medicinal (TCM) plant-derived schaftoside shows promise as a potential drug candidate for COVID-19 treatment. However, the biosynthetic pathway of schaftoside in TCM plants remains unknown. In this study, the genome of the TCM herb Grona styracifolia (Osbeck) H.Ohashi & K.Ohashi (GSO), which is rich in schaftoside, was sequenced, and a high-quality assembly of GSO genome was obtained. Our findings revealed that GSO did not undergo recent whole genome duplication (WGD) but shared an ancestral papilionoid polyploidy event, leading to the gene expansion of chalcone synthase (CHS) and isoflavone 2'-hydroxylase (HIDH). Furthermore, GSO-specific tandem gene duplication resulted in the gene expansion of C-glucosyltransferase (CGT). Integrative analysis of the metabolome and transcriptome identified 13 CGTs and eight HIDHs involved in the biosynthetic pathway of schaftoside. Functional studies indicated that CGTs and HIDHs identified here are bona fide responsible for the biosynthesis of schaftoside in GSO, as confirmed through hairy root transgenic system and in vitro enzyme activity assay. Taken together, the ancestral papilionoid polyploidy event expanding CHSs and HIDHs, along with the GSO-specific tandem duplication of CGT, contributes, partially if not completely, to the robust biosynthesis of schaftoside in GSO. These findings provide insights into the genomic mechanisms underlying the abundant biosynthesis of schaftoside in GSO, highlighting the potential of GSO as a source of bioactive compounds for pharmaceutical development.

Near telomere-to-telomere genome of the model plant Physcomitrium patens.

The model plant Physcomitrium patens has played a pivotal role in enhancing our comprehension of plant evolution and development. However, the current genome harbours numerous regions that remain unfinished and erroneous. To address these issues, we generated an assembly using Oxford Nanopore reads and Hi-C mapping. The assembly incorporates telomeric and centromeric regions, thereby establishing it as a near telomere-to-telomere genome except a region in chromosome 1 that is not fully assembled due to its highly repetitive nature. This near telomere-to-telomere genome resolves the chromosome number at 26 and provides a gap-free genome assembly as well as updated gene models to aid future studies using this model organism.

Genomic and Transcriptomic Insight of Giant Sclerotium Formation of Wood-Decay Fungi.

Many fungi form persistent and dormant sclerotia with compact hardened mycelia during unfavorable circumstances. While most of these sclerotia are small in size, Wolfiporia cocos, a wood-decay fungus, grows into giant sclerotia, which are mainly composed of polysaccharides of linear (1→3)-ß-D-glucans. To explore the underlying mechanism of converting sophisticated wood polysaccharides for biosynthesis of highly homogenized glucans in W. cocos, we sequenced and assembled the genome of a cultivated W. cocos strain (WCLT) in China. The 62-Mb haploid genome contains 44.2% repeat sequences, of which, 48.0% are transposable elements (TEs). Contrary to the genome of W. cocos from North America, WCLT has independently undergone a partial genome duplication (PGD) event. The large-scale TE insertion and PGD occurrence overlapped with an archeological Pleistocene stage of low oxygen and high temperature, and these stresses might have induced the differences in sclerotium due to geographical distribution. The wood decomposition enzymes, as well as sclerotium-regulator kinases, aquaporins, and highly expanded gene families such as NAD-related families, together with actively expressed 1,3-ß-glucan synthase for sclerotium polysaccharides, all have contributed to the sclerotium formation and expansion. This study shall inspire further exploration on how fungi convert wood into simple glucans in the sclerotium of W. cocos.

The Taxus genome provides insights into paclitaxel biosynthesis.

The ancient gymnosperm genus Taxus is the exclusive source of the anticancer drug paclitaxel, yet no reference genome sequences are available for comprehensively elucidating the paclitaxel biosynthesis pathway. We have completed a chromosome-level genome of Taxus chinensis var. mairei with a total length of 10.23 gigabases. Taxus shared an ancestral whole-genome duplication with the coniferophyte lineage and underwent distinct transposon evolution. We discovered a unique physical and functional grouping of CYP725As (cytochrome P450) in the Taxus genome for paclitaxel biosynthesis. We also identified a gene cluster for taxadiene biosynthesis, which was formed mainly by gene duplications. This study will facilitate the elucidation of paclitaxel biosynthesis and unleash the biotechnological potential of Taxus.

A chromosome-level genome assembly of Pyropia haitanensis (Bangiales, Rhodophyta).

Pyropia haitanensis (Bangiales, Rhodophyta), a major economically important marine crop, is also considered as an ideal research model of Rhodophyta to address several major biological questions such as sexual reproduction and adaptation to intertidal abiotic stresses. However, comparative genomic analysis to decipher the underlying molecular mechanisms is hindered by the lack of high-quality genome information. Therefore, we integrated sequencing data from Illumina short-read sequencing, PacBio single-molecule sequencing and BioNano optical genome mapping. The assembled genome was approximately 53.3 Mb with an average GC% of 67.9%. The contig N50 and scaffold N50 were 510.3 kb and 5.8 Mb, respectively. Additionally, 10 superscaffolds representing 80.9% of the total assembly (42.7 Mb) were anchored and orientated to the 5 linkage groups based on markers and genetic distance; this outcome is consistent with the karyotype of five chromosomes (n = 5) based on cytological observation in P. haitanensis. Approximately 9.6% and 14.6% of the genomic region were interspersed repeat and tandem repeat elements, respectively. Based on full-length transcriptome data generated by PacBio, 10,903 protein-coding genes were identified. The construction of a genome-wide phylogenetic tree demonstrated that the divergence time of P. haitanensis and Porphyra umbilicalis was ~204.4 Ma. Interspecies comparison revealed that 493 gene families were expanded and that 449 were contracted in the P. haitanensis genome compared with those in the Po. umbilicalis genome. The genome identified is of great value for further research on the genome evolution of red algae and genetic adaptation to intertidal stresses.

Pyropia yezoensis genome reveals diverse mechanisms of carbon acquisition in the intertidal environment.

Changes in atmospheric CO2 concentration have played a central role in algal and plant adaptation and evolution. The commercially important red algal genus, Pyropia (Bangiales) appears to have responded to inorganic carbon (Ci) availability by evolving alternating heteromorphic generations that occupy distinct habitats. The leafy gametophyte inhabits the intertidal zone that undergoes frequent emersion, whereas the sporophyte conchocelis bores into mollusk shells. Here, we analyze a high-quality genome assembly of Pyropia yezoensis to elucidate the interplay between Ci availability and life cycle evolution. We find horizontal gene transfers from bacteria and expansion of gene families (e.g. carbonic anhydrase, anti-oxidative related genes), many of which show gametophyte-specific expression or significant up-regulation in gametophyte in response to dehydration. In conchocelis, the release of HCO3- from shell promoted by carbonic anhydrase provides a source of Ci. This hypothesis is supported by the incorporation of 13C isotope by conchocelis when co-cultured with 13C-labeled CaCO3.

Gene expression profiles of Pyropia yezoensis in response to dehydration and rehydration stresses.

Pyropia yezoensis is an economically important marine macroalgae, naturally distributed in the upper intertidal zone. Owing to the nature of its habitat, the thallus will periodically be exposed to seawater or atmosphere, and can lose up to 95% of its cellular water content. This makes the alga an ideal research model to investigate the mechanisms of desiccation tolerance. In this study, we investigated the response mechanisms to dehydration and rehydration stresses at the transcription level in Pyropia yezoensis. The differently expressed genes were analyzed based on the different functions of encoding proteins: effector proteins (chloroplast proteins, macromolecular protective substances, and toxicity degradation enzymes) and regulatory proteins (protein kinases and phosphatases). Under osmotic stress, the unigenes related to photosynthesis were down-regulated significantly while those encoding glutathione transferase, superoxide dismutase and heat shock proteins were up-regulated significantly. We inferred that the photosynthetic activity was reduced to prevent damage caused by photosynthetic by-products and that the expression of antioxidant enzyme was increased to prevent the damage associated with reactive oxygen species. Additionally, unigenes encoding serine/threonine kinases and phospholipases were up-regulated in response to osmotic stress, indicating that these kinases play an important role in osmotolerance. Our work will serve as an essential foundation for the understanding of desiccation tolerance mechanisms in Pyropia yezoensis in the upper intertidal zones of rocky coasts.

The first plastid genome of a filamentous taxon 'Bangia' sp. OUCPT-01 in the Bangiales.

Red algae are important primary photosynthetic organisms. The Bangiales comprise a morphologically diverse order of red algae. Until now, complete plastid genomes of the Bangiales were only mapped for foliose species. To date, no filamentous plastomes have been published. The aim of this study was to determine and analyze the complete plastid genome of the filamentous marine species 'Bangia' sp. OUCPT-01. It is a circular molecule, 196,913 bps in length with a guanine-cytosine (GC) content of 33.5%. It has a quadripartite structure with two single copy regions separated by two direct non-identical repeats. It has 205 protein-coding genes, 37 tRNAs, and 6 rRNAs. Therefore, it has a high coding capacity and is highly similar to other Bangiales species in terms of content and structure. In particular, it reveals that the genera in the Bangiales have highly conserved gene content and plastome synteny. This plastome and existing data provide insights into the phylogenetic relationships among the Bangiales genera of the Rhodophyta. According to its plastid- and mitochondrial genomes, 'Bangia 2' is a sister group to Porphyra. However, the position of Wildemania schizophylla in the Bangiales is still controversial. Our results show that the Bangiales divergence time was ~225 million years ago.

The complete mitochondrial genome of Tringa semipalmata inornata (Charadriiformes; Scolopacidae).

In this study, we presented the complete mitochondrial genome of Tringa semipalmata. The circular genome is 16,603 bp in length and contains 13 protein-coding genes (PCGs), 22 transfer RNA (tRNA) genes, 2 ribosome RNA genes and 1 D-loop control regions. The overall nucleotide composition is as follows: 31.2% A, 25.2% T, 29.9% C and 13.6% G, with a total G + C content of 43.53%. The phylogenetic tree was constructed to validate the taxonomic status of T. semipalmata, exhibiting it a close relationship to other Tringa species.

The complete mitochondrial genome of northern grasshopper mouse (Onychomys leucogaster).

In this study, we presented the complete mitochondrial genome of northern grasshopper mouse (Onychomys leucogaster). The circular genome is 16,370 bp in length and contains 13 protein-coding genes (PCGs), 22 transfer RNA (tRNA) genes, 2 ribosome RNA genes, and 1 D-loop control regions. The overall nucleotide composition is: 31.2% A, 25.2% T, 29.9% C, and 13.6% G, with a total G + C content of 43.53%. The phylogenetic tree was constructed to validate the taxonomic status of Onychomys leucogaster, exhibiting a closest relationship with Neotoma fuscipes.

Characterization of the complete plastid genome of Porphyridium purpureum strain CCMP1328.

In this study, the complete plastid genome of Porphyridium purpureum strain CCMP1328 was recovered through Illumina sequencing data. This complete plastid genome of P. purpureum was 220,483 bp in length and contained a pair of IR regions (4604 bp). The pt genome of P. purpureum encoded 234 genes including 199 protein-coding genes, 29 tRNA genes, one tmRNA, and six ribosomal RNA genes in IR regions. The overall GC content of P. purpureum cp genome is 30.4%. By phylogenetic analysis using 18S DNA fragments through NJ method, P. purpureum strain CCMP1328 was grouped in the P. purpureum cluster without further distinction. This complete plastid genomes can be subsequently used for evolution studies of red algae and provide valuable insight into dynamic evolution of group II introns.