The chromosome-level wintersweet (Chimonanthus praecox) genome provides insights into floral scent biosynthesis and flowering in winter

From sequences to sustainability: Exploring dipterocarp genomes for oleoresin production, timber quality, and conservation

Dipterocarp species dominate tropical forest ecosystems and provide key ecological and economic value through their use of aromatic resins, medicinal chemicals, and high-quality timber. However, habitat loss and unsustainable logging have endangered many Dipterocarpaceae species. Genomic strategies provide new opportunities for both elucidating the molecular pathways underlying these desirable traits and informing conservation efforts for at-risk taxa. This review summarizes the progress in dipterocarp genomics analysis and applications. We describe 16 recently published Dipterocarpaceae genome sequences, representing crucial genetic blueprints. Phylogenetic comparisons delineate evolutionary relationships among species and provide frameworks for pinpointing functional changes underlying specialized metabolism and wood development patterns. We also discuss connections revealed thus far between specific gene families and both oleoresin biosynthesis and wood quality traits-including the identification of key terpenoid synthases and cellulose synthases likely governing pathway flux. Moreover, the characterization of adaptive genomic markers offers vital resources for supporting conservation practices prioritizing resilient genotypes displaying valuable oleoresin and timber traits. Overall, progress in dipterocarp functional and comparative genomics provides key tools for addressing the intertwined challenges of preserving biodiversity in endangered tropical forest ecosystems while sustainably deriving aromatic chemicals and quality lumber that support diverse human activities.

High-quality reference genome of cowpea beetle Callosobruchus maculatus

Callosobruchus maculatus is one of the most competitive stored grain pests, which causes a great loss to agricultural economy. However, due to an inadequacy of high-quality reference genome, the molecular mechanisms for olfactory and hypoxic adaptations to stored environments are unknown and require to be revealed urgently, which will contribute to the detection and prevention of the invasive pests C. maculatus. Here, we presented a high-quality chromosome-level genome of C. maculatus based on Illumina, Nanopore and Hi-C sequencing data. The total size was 1.2 Gb, and 65.17% (797.47 Mb) of it was identified to be repeat sequences. Among assembled chromosomes, chromosome 10 was considered the X chromosome according to the evidence of reads coverage and homologous genes among species. The current version of high-quality genome provides preferable data resources for the adaptive evolution research of C. maculatus.

Multi-omics analyses and botanical perfumer hypothesis provide insights into the formation and maintenance of aromatic characteristics of Dendrobium loddigesii flowers

Dendrobium loddigesii, a member of the Orchidaceae family, is a valuable horticultural crop known for its aromatic qualities. However, the mechanisms responsible for the development of its aromatic characteristics remain poorly understood. To elucidate these underlying mechanisms, we assembled the first chromosome-level reference genome of D. loddigesii using PacBio HiFi-reads, Illumina short-reads, and Hi-C data. The assembly comprises 19 pseudochromosomes with N50 contig and N50 scaffold sizes of 55.15 and 89.94 Mb, respectively, estimating the genome size to be 1.68 Gb, larger than that of other sequenced Dendrobium species. During the flowering stages, we conducted a comprehensive analysis combining volatilomics and transcriptomics to understand the characteristics and biosynthetic mechanisms pathways of the floral scent. Our findings emphasize the significant contribution of aromatic terpenoids, especially monoterpenoids, in defining the floral aroma. Furthermore, we identified two crucial terpene synthase (TPS) genes that play a key role in maintaining the aroma during flowering. Through the integration volatilomics data with catalytic assays of DlTPSbs proteins, we identified specific compounds responsible for the aromatic characteristics of D. loddigesii. This integrated analysis of the genome, transcriptome, and volatilome, offers valuable insights into the development and preservation of D. loddigesii's aromatic characteristics, setting the stage for further exploration of the botanical perfumer hypothesis.

The chromosome-level genomes of the herbal magnoliids Warburgia ugandensis and Saururus chinensis

Warburgia ugandensis and Saururus chinensis are two of the most important medicinal plants in magnoliids and are widely utilized in traditional Kenya and Chinese medicine, respectively. The absence of higher-quality reference genomes has hindered research on the medicinal compound biosynthesis mechanisms of these plants. We report the chromosome-level genome assemblies of W. ugandensis and S. chinensis, and generated 1.13 Gb and 0.53 Gb genomes from 74 and 27 scaffolds, respectively, using BGI-DIPSEQ, Nanopore, and Hi-C sequencing. The scaffold N50 lengths were 82.97 Mb and 48.53 Mb, and the assemblies were anchored to 14 and 11 chromosomes of W. ugandensis and S. chinensis, respectively. In total, 24,739 and 20,561 genes were annotated, and 98.5% and 98% of the BUSCO genes were fully represented, respectively. The chromosome-level genomes of W. ugandensis and S. chinensis will be valuable resources for understanding the genetics of these medicinal plants, studying the evolution of magnoliids and angiosperms and conserving plant genetic resources.

A high-quality haplotype genome of Michelia alba DC reveals differences in methylation patterns and flower characteristics

Michelia alba DC is a highly valuable ornamental plant of the Magnoliaceae family. This evergreen tropical tree commonly grows in Southeast Asia and is adored for its delightful fragrance. Our study assembled the M. alba haplotype genome MC and MM by utilizing Nanopore ultralong reads, Pacbio Hifi long reads and parental second-generation data. Moreover, the first methylation map of Magnoliaceae was constructed based on the methylation site data obtained using Nanopore data. Metabolomic datasets were generated from the flowers of three different species to assess variations in pigment and volatile compound accumulation. Finally, transcriptome data were generated to link genomic, methylation, and morphological patterns to reveal the reasons underlying the differences between M. alba and its parental lines in petal color, flower shape, and fragrance. We found that the AP1 and AP2 genes are crucial in M. alba petal formation, while the 4CL, PAL, and C4H genes control petal color. The data generated in this study serve as a foundation for future physiological and biochemical research on M. alba, facilitate the targeted improvement of M. alba varieties, and offer a theoretical basis for molecular research on Michelia L.

Using leaf economic spectrum and photosynthetic acclimation to evaluate the potential performance of wintersweet under future climate conditions

The function of landscape plants on the ecosystem can alleviate environmental issues of urbanization and global change. Global changes due to elevated CO2 affect plant growth and survival, but there is a lack of quantitative methods to evaluate the adaptability of landscape plants to future climate conditions. Leaf traits characterized by leaf economic spectrum (LES) are the universal currency for predicting the impact on plant ecosystem functions. Elevated CO2 usually leads to photosynthetic acclimation (PC), characterised by decreased photosynthetic capacity. Here, we proposed a theoretical and practical framework for the use of LES and PC to project the potential performance of landscape plants under future climatic conditions through principal component analysis, structural equation modelling, photosynthetic restriction analysis and nitrogen allocation analysis. We used wintersweet (an important landscaping species) to test the feasibility of this framework under elevated CO2 and different nitrogen (N) supplies. We found that elevated CO2 decreased the specific leaf area but increased leaf N concentration. The results suggest wintersweet may be characterized by an LES with high leaf construction costs, low photosynthetic return, and robust stress resistance. Elevated CO2 reduced photosynthetic capacity and stomatal conductance but increased photosynthetic rate and leaf area. These positive physio-ecological traits, e.g., larger leaf area (canopy), higher water use efficiency and stress resistance, may lead to improved performance of wintersweet under the predicted future climatic conditions. The results suggest planting more wintersweet in urban landscaping may be an effective adaptive strategy to climate change.

Unveiling the aesthetic secrets: exploring connections between genetic makeup, chemical, and environmental factors for enhancing/improving the color and fragrance/aroma of Chimonanthus praecox

Floral color and scent profiles vary across species, geographical locations, and developmental stages. The exclusive floral color and fragrance of Chimonanthus praecox is contributed by a range of endogenous chemicals that distinguish it from other flowers and present amazing ornamental value. This comprehensive review explores the intricate interplay of environmental factors, chemicals and genes shaping the flower color and fragrance of Chimonanthus praecox. Genetic and physiological factors control morpho-anatomical attributes as well as pigment synthesis, while environmental factors such as temperature, light intensity, and soil composition influence flower characteristics. Specific genes control pigment synthesis, and environmental factors such as temperature, light intensity, and soil composition influence flower characteristics. Physiological processes including plant hormone contribute to flower color and fragrance. Hormones, notably ethylene, exert a profound influence on varioustraits. Pigment investigations have spotlighted specific flavonoids, including kaempferol 3-O-rutinoside, quercetin, and rutin. Red tepals exhibit unique composition with cyanidin-3-O-rutinoside and cyanidin-3-O-glucoside being distinctive components. Elucidating the molecular basis of tepal color variation, particularly in red and yellow varieties, involves the identification of crucial regulatory genes. In conclusion, this review unravels the mysteries of Chimonanthus praecox, providing a holistic understanding of its flower color and fragrance for landscape applications. This comprehensive review uniquely explores the genetic intricacies, chemical and environmental influences that govern the mesmerizing flower color and fragrance of Chimonanthus praecox, providing valuable insights for its landscape applications. This review article is designed for a diverse audience, including plant geneticists, horticulturists, environmental scientists, urban planners, and students, offering understandings into the genetic intricacies, ecological significance, and practical applications of Chimonanthus praecox across various disciplines. Its appeal extends to professionals and enthusiasts interested in plant biology, conservation, and industries dependent on unique floral characteristics.

Chromosome-level genome assembly provides insights into the genome evolution and functional importance of the phenylpropanoid-flavonoid pathway in Thymus mongolicus

BACKGROUND

Thymus mongolicus (family Lamiaceae) is a Thyme subshrub with strong aroma and remarkable environmental adaptability. Limited genomic information limits the use of this plant.

RESULTS

Chromosome-level 605.2 Mb genome of T. mongolicus was generated, with 96.28% anchored to 12 pseudochromosomes. The repetitive sequences were dominant, accounting for 70.98%, and 32,593 protein-coding genes were predicted. Synteny analysis revealed that Lamiaceae species generally underwent two rounds of whole genome duplication; moreover, species-specific genome duplication was identified. A recent LTR retrotransposon burst and tandem duplication might play important roles in the formation of the Thymus genome. Using comparative genomic analysis, phylogenetic tree of seven Lamiaceae species was constructed, which revealed that Thyme plants evolved recently in the family. Under the phylogenetic framework, we performed functional enrichment analysis of the genes on nodes that contained the most gene duplication events (> 50% support) and of relevant significant expanded gene families. These genes were highly associated with environmental adaptation and biosynthesis of secondary metabolites. Combined transcriptome and metabolome analyses revealed that Peroxidases, Hydroxycinnamoyl-CoA shikimate/quinate hydroxycinnamoyl transferases, and 4-coumarate-CoA ligases genes were the essential regulators of the phenylpropanoid-flavonoid pathway. Their catalytic products (e.g., apigenin, naringenin chalcone, and several apigenin-related compounds) might be responsible for the environmental tolerance and aromatic properties of T. mongolicus.

CONCLUSION

This study enhanced the understanding of the genomic evolution of T. mongolicus, enabling further exploration of its unique traits and applications, and contributed to the understanding of Lamiaceae genomics and evolutionary biology.

Transcriptome and volatile compounds analyses of floral development provide insight into floral scent formation in Paeonia lactiflora 'Wu Hua Long Yu'

Herbaceous peony (Paeonia lactiflora) is a well-known ornamental plant in China, celebrated for its beautiful flowers that can emit fragrances. However, exact molecular mechanisms governing synthesis of floral volatiles within herbaceous peony remain unclear. To address this gap in knowledge, our study focused on analyzing the transcriptome and the levels of floral volatile compounds in P. lactiflora 'Wu Hua Long Yu' at different stages of flower development. Using gas chromatography-mass spectrometry (GC-MS), we obtained eighteen major volatile compounds, with monoterpenes being the dominant components among them. Our transcriptome analysis, based on pooled sequencing data, revealed the most differentially expressed genes (DEGs) existed between stages S1 and S3 of flower development. Among these DEGs, we identified 89 functional genes associated with the synthesis of volatile monoterpenes, with 28 of these genes showing a positive correlation with the release of monoterpenes. Specifically, key regulators of monoterpene synthesis in herbaceous peony appear to be 1-deoxy-D-xylulose 5-phosphate synthase (DXS), geranyl pyrophosphate synthase (GPPS), and terpene synthase (TPS). Additionally, our study identified some transcription factors (TFs) that may be involved in the biosynthesis of monoterpenes. These discoveries offer invaluable illumination into the intricate molecular underpinnings orchestrating the generation of floral fragrances in herbaceous peonies, and they offer a foundation for further research to identify and utilize candidate gene resources for this purpose.

Integrated transcriptome and proteome analysis provides insights into CpFPA1 for floral induction in Chimonanthus praecox (Magnoliidae) without FLC in genome

KEY MESSAGE

We used transcriptomic and proteomic association analysis to reveal the critical genes/proteins at three key flower bud differentiation stages and overexpression of CpFPA1 in Arabidopsis resulted in earlier flowering. Wintersweet (Chimonanthus praecox), a rare winter-flowering woody plant, is well known for its unique blooming time, fragrance and long flowering period. However, the molecular mechanism of flowering in C. praecox remains poorly unclear. In this study, we used transcriptomic and proteomic association analysis to reveal the critical genes/proteins at three key flower bud (FB) differentiation stages (FB.Apr, FB.May and FB.Nov) in C. praecox. The results showed that a total of 952 differential expressed genes (DEGs) and 40 differential expressed proteins (DEPs) were identified. Gene ontology (GO) enrichment revealed that DEGs in FB.Apr/FB.May comparison group were mainly involved in metabolic of biological process, cell and cell part of cellular component and catalytic activity of molecular function. In the EuKaryotic Orthologous Groups (KOG) functional classification, DEPs were predicted mainly in the function of general function prediction only (KOG0118), post-translational modification, protein turnover and chaperones. The autonomous pathway genes play an essential role in the floral induction. Based on transcriptome and proteome correlation analysis, six candidate genes associated with the autonomous pathway were identified, including FPA1, FPA2a, FPA2b, FCA, FLK, FY. Furthermore, CpFPA1 was isolated and functionally characterized, and ectopic expression of CpFPA1 in Arabidopsis Columbia (Col-0) resulted in earlier flowering. These data could contribute to understand the function of CpFPA1 for floral induction and provide information for further research on the molecular mechanisms of flowering in wintersweet.

Characterization of the Complete Mitochondrial Genome of Wintersweet (Chimonanthus praecox) and Comparative Analysis within Magnoliids

Mitochondrial genome sequencing is a valuable tool for investigating mitogenome evolution, species phylogeny, and population genetics. Chimonanthus praecox (L.) Link, also known as "La Mei" in Chinese, is a famous ornamental and medical shrub belonging to the order Laurales of the Calycanthaceae family. Although the nuclear genomes and chloroplast genomes of certain Laurales representatives, such as Lindera glauca, Laurus nobilis, and Piper nigrum, have been sequenced, the mitochondrial genome of Laurales members remains unknown. Here, we reported the first complete mitogenome of C. praecox. The mitogenome was 972,347 bp in length and comprised 60 unique coding genes, including 40 protein-coding genes (PCGs), 17 tRNA genes, and three rRNA genes. The skewness of the PCGs showed that the AT skew (-0.0096233) was negative, while the GC skew (0.031656) was positive, indicating higher contents of T's and G's in the mitochondrial genome of C. praecox. The Ka/Ks ratio analysis showed that the Ka/Ks values of most genes were less than one, suggesting that these genes were under purifying selection. Furthermore, there is a substantial abundance of dispersed repeats in C. praecox, constituting 16.98% of the total mitochondrial genome. A total of 731 SSR repeats were identified in the mitogenome, the highest number among the eleven available magnoliids mitogenomes. The mitochondrial phylogenetic analysis based on 29 conserved PCGs placed the C. praecox in Lauraceae, and supported the sister relationship of Laurales with Magnoliales, which was congruent with the nuclear genome evidence. The present study enriches the mitogenome data of C. praecox and promotes further studies on phylogeny and plastid evolution.

Polyploid Genome Assembly Provides Insights into Morphological Development and Ascorbic Acid Accumulation of Sauropus androgynus

Sauropus androgynus (S. androgynus) (2n = 4x = 52) is one of the most popular functional leafy vegetables in South and Southeast Asia. With its rich nutritional and pharmaceutical values, it has traditionally had widespread use for dietary and herbal purposes. Here, the genome of S. androgynus was sequenced and assembled, revealing a genome size of 1.55 Gb with 26 pseudo-chromosomes. Phylogenetic analysis traced back the divergence of Sauropus from Phyllanthus to approximately 29.67 million years ago (Mya). Genome analysis revealed that S. androgynus polyploidized around 20.51 Mya and shared a γ event about 132.95 Mya. Gene function analysis suggested that the expansion of pathways related to phloem development, lignin biosynthesis, and photosynthesis tended to result in the morphological differences among species within the Phyllanthaceae family, characterized by varying ploidy levels. The high accumulation of ascorbic acid in S. androgynus was attributed to the high expression of genes associated with the L-galactose pathway and recycling pathway. Moreover, the expanded gene families of S. androgynus exhibited multiple biochemical pathways associated with its comprehensive pharmacological activity, geographic adaptation and distinctive pleasurable flavor. Altogether, our findings represent a crucial genomic asset for S. androgynus, casting light on the intricate ploidy within the Phyllanthaceae family.

Contemporary understanding of transcription factor regulation of terpenoid biosynthesis in plants

KEY MESSAGE

This review summarized how TFs function independently or in response to environmental factors to regulate terpenoid biosynthesis via fine-tuning the expression of rate-limiting enzymes. Terpenoids are derived from various species and sources. They are essential for interacting with the environment and defense mechanisms, such as antimicrobial, antifungal, antiviral, and antiparasitic properties. Almost all terpenoids have high medicinal value and economic performance. Recently, the control of enzyme genes on terpenoid biosynthesis has received a great deal of attention, but transcriptional factors regulatory network on terpenoid biosynthesis and accumulation has yet to get a thorough review. Transcription factors function as activators or suppressors independently or in response to environmental stimuli, fine-tuning terpenoid accumulation through regulating rate-limiting enzyme expression. This study investigates the advancements in transcription factors related to terpenoid biosynthesis and systematically summarizes previous works on the specific mechanisms of transcription factors that regulate terpenoid biosynthesis via hormone signal-transcription regulatory networks in plants. This will help us to better comprehend the regulatory network of terpenoid biosynthesis and build the groundwork for terpenoid development and effective utilization.

Genome-wide identification and analysis of the evolution and expression pattern of the SBP gene family in two Chimonanthus species

BACKGROUND

Chimonanthus praecox and Chimonanthus salicifolius are closely related species that diverged approximately six million years ago. While both C. praecox and C. salicifolius could withstand brief periods of low temperatures of - 15 °C. Their flowering times are different, C. praecox blooms in early spring, whereas C. salicifolius blooms in autumn. The SBP-box (SQUAMOSA promoter-binding protein) is a plant-specific gene family that plays a crucial vital role in regulating plant flowering. Although extensively studied in various plants, the SBP gene family remains uncharacterized in Calycanthaceae.

METHODS AND RESULTS

We conducted genome-wide identification of SBP genes in both C. praecox and C. salicifolius and comprehensively characterized the chromosomal localization, gene structure, conserved motifs, and domains of the identified SBP genes. In total, 15 and 18 SBP genes were identified in C. praecox and C. salicifolius, respectively. According to phylogenetic analysis, the SBP genes from Arabidopsis, C. praecox, and C. salicifolius were clustered into eight groups. Analysis of the gene structure and conserved protein motifs showed that SBP proteins of the same subfamily have similar motif structures. The expression patterns of SBP genes were analyzed using transcriptome data. The results revealed that more than half of the genes exhibited lower expression levels in leaves than in flowers, suggesting their potential involvement in the flower development process and may be linked to the winter and autumn flowering of C. praecox and C. salicifolius.

CONCLUSION

Thirty-three SBPs were identified in C. praecox and C. salicifolius. The evolutionary characteristics and expression patterns were examined in this study. These results provide valuable information to elucidate the evolutionary relationships of the SBP family and help determine the functional characteristics of the SBP genes in subsequent studies.

Unlocking secrets of nature's chemists: Potential of CRISPR/Cas-based tools in plant metabolic engineering for customized nutraceutical and medicinal profiles

Plant species have evolved diverse metabolic pathways to effectively respond to internal and external signals throughout their life cycle, allowing adaptation to their sessile and phototropic nature. These pathways selectively activate specific metabolic processes, producing plant secondary metabolites (PSMs) governed by genetic and environmental factors. Humans have utilized PSM-enriched plant sources for millennia in medicine and nutraceuticals. Recent technological advances have significantly contributed to discovering metabolic pathways and related genes involved in the biosynthesis of specific PSM in different food crops and medicinal plants. Consequently, there is a growing demand for plant materials rich in nutrients and bioactive compounds, marketed as "superfoods". To meet the industrial demand for superfoods and therapeutic PSMs, modern methods such as system biology, omics, synthetic biology, and genome editing (GE) play a crucial role in identifying the molecular players, limiting steps, and regulatory circuitry involved in PSM production. Among these methods, clustered regularly interspaced short palindromic repeats-CRISPR associated protein (CRISPR/Cas) is the most widely used system for plant GE due to its simple design, flexibility, precision, and multiplexing capabilities. Utilizing the CRISPR-based toolbox for metabolic engineering (ME) offers an ideal solution for developing plants with tailored preventive (nutraceuticals) and curative (therapeutic) metabolic profiles in an ecofriendly way. This review discusses recent advances in understanding the multifactorial regulation of metabolic pathways, the application of CRISPR-based tools for plant ME, and the potential research areas for enhancing plant metabolic profiles.

Genome-wide identification and analysis of MIKC-type MADS-box genes expression in Chimonanthus salicifolius

BACKGROUND

MIKC type MADS-box transcription factors are one of the largest gene families and play a pivotal role in flowering time and flower development. Chimonanthus salicifolius belongs to the family Calycanthaceae and has a unique flowering time and flowering morphology compared to other Chimonanthus species, but the research on MIKC type MADS-box gene family of C. salicifolius has not been reported.

OBJECTIVE

Identification, comprehensive bioinformatic analysis, the expression pattern of MIKC-type MADS-box gene family from different tissues of C. salicifolius.

METHODS

Genome-wide investigation and expression pattern under different tissues of the MIKC-type MADS-box gene family in C. salicifolius, and their phylogenetic relationships, evolutionary characteristics, gene structure, motif distribution, promoter cis-acting element were performed.

RESULTS

A total of 29 MIKC-type MADS-box genes were identified from the whole genome sequencing. Interspecies synteny analysis revealed more significant collinearity between C. salicifolius and the magnoliids species compared to eudicots and monocots. MIKC-type MADS-box genes from the same subfamily share similar distribution patterns, gene structure, and expression patterns. Compared with Arabidopsis thaliana, Nymphaea colorata, and Chimonanthus praecox, the FLC genes were absent in C. salicifolius, while the AGL6 subfamily was expanded in C. salicifolius. The selectively expanded promoter (AGL6) and lack of repressor (FLC) genes may explain the earlier flowering in C. salicifolius. The loss of the AP3 homologous gene in C. salicifolius is probably the primary cause of the morphological distinction between C. salicifolius and C. praecox. The csAGL6a gene is specifically expressed in the flowering process and indicates the potential function of promoting flowering.

CONCLUSION

This study offers a genome-wide identification and expression profiling of the MIKC-types MADS-box genes in the C. salicifolius, and establishes the foundation for screening flowering development genes and understanding the potential function of the MIKC-types MADS-box genes in the C. salicifolius.

Genome-wide high-throughput chromosome conformation capture analysis reveals hierarchical chromatin interactions during early somatic embryogenesis

Somatic embryogenesis (SE), like zygotic embryo development, is a progressive process. Early SE is the beginning of a switch from a somatic to an embryogenic state and is an important stage for initiating chromatin reprogramming of SE. Previous studies suggest that changes in chromatin accessibility occur during early SE, although information on the 3D structure of chromatin is not yet available. Here, we present a chromosome-level genome assembly of longan (Dimocarpus longan) using PacBio combined with high-through chromosome conformation capture scaffolding, which resulted in a 446 Mb genome assembly anchored onto 15 scaffolds. During early SE, chromatin was concentrated and then decondensed, and a large number of long terminal repeat retrotransposons (LTR-RTs) were enriched in the local chromatin interaction region, suggesting LTR-RTs were involved in chromatin reorganization. Early SE was accompanied by the transformation from A to B compartments, and the interactions between B compartments were enhanced. Results from chromatin accessibility, monomethylation of histone H3 at lysine 4 (H3K4me1) modification, and transcription analyses further revealed a gene regulatory network for cell wall thickening during SE. Particularly, we found that the H3K4me1 differential peak binding motif showed abnormal activation of ethylene response factor transcription factors and participation in SE. The chromosome-level genomic and multiomics analyses revealed the 3D conformation of chromatin during early SE, providing insight into the molecular mechanisms underlying cell wall thickening and the potential regulatory networks of TFs during early SE in D. longan. These results provide additional clues for revealing the molecular mechanisms of plant SE.

Genome-Wide Identification and Expression Analysis of the bHLH Transcription Factor Family in Wintersweet (Chimonanthus praecox)

Wintersweet (Chimonanthus praecox (L.) Link, Calycanthaceae) is an esteemed ornamental flowering shrub known for its distinct blooming period in winter, vibrant color petals, and captivating floral fragrance. Basic helix-loop-helix (bHLH) transcription factors (TFs) play pivotal roles as key regulators in secondary metabolites biosynthesis, growth, and development in plants. However, the systematic analysis of the bHLH family members and their role in the regulation of floral traits in Wintersweet remains insufficiently understood. To bridge this knowledge gap, we conducted a comprehensive genome-wide analysis of the C. praecox bHLH (CpbHLH) gene family, identifying a total of 131 CpbHLH genes across 11 chromosomes. Phylogenetic analysis classified these CpbHLH genes into 23 subfamilies, wherein most members within the same subfamily exhibited analogous intron/exon patterns and motif composition. Moreover, the expansion of the CpbHLH gene family was primarily driven by segmental duplication, with duplicated gene pairs experiencing purifying selection during evolution. Transcriptomic analysis revealed diverse expression patterns of CpbHLH genes in various tissues and distinct stages of Wintersweet flower development, thereby suggesting their involvement in a diverse array of physiological processes. Furthermore, yeast 2-hybrid assay demonstrated interaction between CpbHLH25 and CpbHLH59 (regulators of floral scent and color) as well as with CpbHLH112 and CpMYB2, suggesting potential coordinately regulation of secondary metabolites biosynthesis in Wintersweet flowers. Collectively, our comprehensive analysis provides valuable insights into the structural attributes, evolutionary dynamics, and expression profiles of the CpbHLH gene family, laying a solid foundation for further explorations of the multifaceted physiological and molecular roles of bHLH TFs in Wintersweet.

A chromosome-scale genome assembly of Artemisia argyi reveals unbiased subgenome evolution and key contributions of gene duplication to volatile terpenoid diversity

Artemisia argyi Lévl. et Vant., a perennial Artemisia herb with an intense fragrance, is widely used in traditional medicine in China and many other Asian countries. Here, we present a chromosome-scale genome assembly of A. argyi comprising 3.89 Gb assembled into 17 pseudochromosomes. Phylogenetic and comparative genomic analyses revealed that A. argyi underwent a recent lineage-specific whole-genome duplication (WGD) event after divergence from Artemisia annua, resulting in two subgenomes. We deciphered the diploid ancestral genome of A. argyi, and unbiased subgenome evolution was observed. The recent WGD led to a large number of duplicated genes in the A. argyi genome. Expansion of the terpene synthase (TPS) gene family through various types of gene duplication may have greatly contributed to the diversity of volatile terpenoids in A. argyi. In particular, we identified a typical germacrene D synthase gene cluster within the expanded TPS gene family. The entire biosynthetic pathways of germacrenes, (+)-borneol, and (+)-camphor were elucidated in A. argyi. In addition, partial deletion of the amorpha-4,11-diene synthase (ADS) gene and loss of function of ADS homologs may have resulted in the lack of artemisinin production in A. argyi. Our study provides new insights into the genome evolution of Artemisia and lays a foundation for further improvement of the quality of this important medicinal plant.

Chromosome-level reference genome of Tetrastigma hemsleyanum (Vitaceae) provides insights into genomic evolution and the biosynthesis of phenylpropanoids and flavonoids

Here, we present a high-quality chromosome-scale genome assembly (2.19 Gb) and annotation of Tetrastigma hemsleyanum, a perennial herbaceous liana native to subtropical China with diverse medicinal applications. Approximately 73% of the genome was comprised of transposable elements (TEs), of which long terminal repeat retrotransposons (LTR-RTs) were a predominant group (69% of the genome). The genome size increase of T. hemsleyanum (relative to Vitis species) was mostly due to the proliferation of LTR-RTs. Of the different modes of gene duplication identified, transposed duplication (TRD) and dispersed duplication (DSD) were the predominant ones. Genes, particularly those involved in the phenylpropanoid-flavonoid (PF) pathway and those associated with therapeutic properties and environmental stress resistance, were significantly amplified through recent tandem duplications. We dated the divergence of two intraspecific lineages in Southwest (SW) versus Central-South-East (CSE) China to the late Miocene (approximately 5.2 million years ago). Of those, the former showed more upregulated genes and metabolites. Based on resequencing data of 38 individuals representing both lineages, we identified various candidate genes related to 'response to stimulus' and 'biosynthetic process', including ThFLS11, which is putatively involved in flavonoid accumulation. Overall, this study provides abundant genomic resources for future evolutionary, ecological, and functional genomics studies in T. hemsleyanum and related species.

A chromosome-level genome assembly of radish (Raphanus sativus L.) reveals insights into genome adaptation and differential bolting regulation

High-quality radish (Raphanus sativus) genome represents a valuable resource for agronomical trait improvements and understanding genome evolution among Brassicaceae species. However, existing radish genome assembly remains fragmentary, which greatly hampered functional genomics research and genome-assisted breeding. Here, using a NAU-LB radish inbred line, we generated a reference genome of 476.32 Mb with a scaffold N50 of 56.88 Mb by incorporating Illumina, PacBio and BioNano optical mapping techniques. Utilizing Hi-C data, 448.12 Mb (94.08%) of the assembled sequences were anchored to nine radish chromosomes with 40 306 protein-coding genes annotated. In total, 249.14 Mb (52.31%) comprised the repetitive sequences, among which long terminal repeats (LTRs, 30.31%) were the most abundant class. Beyond confirming the whole-genome triplication (WGT) event in R. sativus lineage, we found several tandem arrayed genes were involved in stress response process, which may account for the distinctive phenotype of high disease resistance in R. sativus. By comparing against the existing Xin-li-mei radish genome, a total of 2 108 573 SNPs, 7740 large insertions, 7757 deletions and 84 inversions were identified. Interestingly, a 647-bp insertion in the promoter of RsVRN1 gene can be directly bound by the DOF transcription repressor RsCDF3, resulting into its low promoter activity and late-bolting phenotype of NAU-LB cultivar. Importantly, introgression of this 647-bp insertion allele, RsVRN1^In-536 , into early-bolting genotype could contribute to delayed bolting time, indicating that it is a potential genetic resource for radish late-bolting breeding. Together, this genome resource provides valuable information to facilitate comparative genomic analysis and accelerate genome-guided breeding and improvement in radish.

A reference-grade genome assembly for Astragalus mongholicus and insights into the biosynthesis and high accumulation of triterpenoids and flavonoids in its roots

Astragalus membranaceus var. mongholicus (AMM), a member of the Leguminosae, is one of the most important medicinal plants worldwide. The dried roots of AMM have a wide range of pharmacological effects and are a traditional Chinese medicine. Here, we report the first chromosome-level reference genome of AMM, comprising nine pseudochromosomes with a total size of 1.47 Gb and 27 868 protein-encoding genes. Comparative genomic analysis reveals that AMM has not experienced an independent whole-genome duplication (WGD) event after the WGD event shared by the Papilionoideae species. Analysis of long terminal repeat retrotransposons suggests a recent burst of these elements at approximately 0.13 million years ago, which may explain the large size of the AMM genome. Multiple gene families involved in the biosynthesis of triterpenoids and flavonoids were expanded, and our data indicate that tandem duplication has been the main driver for expansion of these families. Among the expanded families, the phenylalanine ammonia-lyase gene family was primarily expressed in the roots of AMM, suggesting their roles in the biosynthesis of phenylpropanoid compounds. The functional versatility of 2,3-oxidosqualene cyclase genes in cluster III may play a critical role in the diversification of triterpenoids in AMM. Our findings provide novel insights into triterpenoid and flavonoid biosynthesis and can facilitate future research on the genetics and medical applications of AMM.

Unique gene duplications and conserved microsynteny potentially associated with resistance to wood decay in the Lauraceae

Wood decay resistance (WDR) is marking the value of wood utilization. Many trees of the Lauraceae have exceptional WDR, as evidenced by their use in ancient royal palace buildings in China. However, the genetics of WDR remain elusive. Here, through comparative genomics, we revealed the unique characteristics related to the high WDR in Lauraceae trees. We present a 1.27-Gb chromosome-level assembly for Lindera megaphylla (Lauraceae). Comparative genomics integrating major groups of angiosperm revealed Lauraceae species have extensively shared gene microsynteny associated with the biosynthesis of specialized metabolites such as isoquinoline alkaloids, flavonoid, lignins and terpenoid, which play significant roles in WDR. In Lauraceae genomes, tandem and proximal duplications (TD/PD) significantly expanded the coding space of key enzymes of biosynthesis pathways related to WDR, which may enhance the decay resistance of wood by increasing the accumulation of these compounds. Among Lauraceae species, genes of WDR-related biosynthesis pathways showed remarkable expansion by TD/PD and conveyed unique and conserved motifs in their promoter and protein sequences, suggesting conserved gene collinearity, gene expansion and gene regulation supporting the high WDR. Our study thus reveals genomic profiles related to biochemical transitions among major plant groups and the genomic basis of WDR in the Lauraceae.

Application of third-generation sequencing to herbal genomics

There is a long history of traditional medicine use. However, little genetic information is available for the plants used in traditional medicine, which limits the exploitation of these natural resources. Third-generation sequencing (TGS) techniques have made it possible to gather invaluable genetic information and develop herbal genomics. In this review, we introduce two main TGS techniques, PacBio SMRT technology and Oxford Nanopore technology, and compare the two techniques against Illumina, the predominant next-generation sequencing technique. In addition, we summarize the nuclear and organelle genome assemblies of commonly used medicinal plants, choose several examples from genomics, transcriptomics, and molecular identification studies to dissect the specific processes and summarize the advantages and disadvantages of the two TGS techniques when applied to medicinal organisms. Finally, we describe how we expect that TGS techniques will be widely utilized to assemble telomere-to-telomere (T2T) genomes and in epigenomics research involving medicinal plants.

Marsdenia tenacissima genome reveals calcium adaptation and tenacissoside biosynthesis

Marsdenia tenacissima is a medicinal plant widely distributed in the calcium-rich karst regions of southwest China. However, the lack of a reference genome has hampered the implementation of molecular techniques in its breeding, pharmacology and domestication. We generated the chromosome-level genome assembly in Apocynaceae using combined SMRT sequencing and Hi-C. The genome length was 381.76 Mb, with 98.9% of it found on 11 chromosomes. The genome contained 222.63 Mb of repetitive sequences and 21 899 predicted gene models, with a contig N50 of 6.57 Mb. Phylogenetic analysis revealed that M. tenacissima diverged from Calotropis gigantea at least 13.43 million years ago. Comparative genomics showed that M. tenacissima underwent ancient shared whole-genome duplication. This event, together with tandem duplication, contributed to 70.71% of gene-family expansion. Both pseudogene analysis and selective pressure calculations suggested calcium-related adaptive evolution in the M. tenacissima genome. Calcium-induced differentially expressed genes (DEGs) were mainly enriched in cell-wall-related processes. Domains (e.g. Fasciclin and Amb_all) and cis-elements (e.g. MYB and MYC) frequently occurred in the coding and promoter regions of cell-wall DEGs, respectively, and the expression levels of these genes correlated significantly with those of calcium-signal-related transcription factors. Moreover, calcium addition increased tenacissoside I, G and H contents. The availability of this high-quality genome provides valuable genomic information for genetic breeding and molecular design, and lends insights into the calcium adaptation of M. tenacissima in karst areas.

Genome-wide analysis of MIKCC-type MADS-box genes and roles of CpFUL/SEP/AGL6 superclade in dormancy breaking and bud formation of Chimonanthus praecox

Wintersweet (Chimonanthus praecox), a Magnoliidae tree, is popular for its unique fragrant aroma and winter-flowering characteristics, which is widely used in gardens and pots, or for cut flowers, essential oil, medicine, and edible products. MIKC^C-type of MADS-box gene family play a crucial role in plant growth and development process, particularly in controlling flowering time and floral organ development. Although MIKC^C-type genes have been well studied in many plant species, the study of MIKC^C-type is poorly in C. praecox. In this study, we identified 30 MIKC^C-type genes of C. praecox on gene structures, chromosomal location, conserved motifs, phylogenetic relationships based on bioinformatics tools. Phylogenetic relationships analysis with Arabidopsis (Arabidopsis thaliana), rice (Oryza sativa Japonica), Amborella trichopoda and tomato (Solanum lycopersicum) showed that CpMIKC^Cs were divided into 13 subclasses, each subclass containing 1 to 4 MIKC^C-type genes. The Flowering locus C (FLC) subfamily was absent in C. praecox genome. CpMIKC^Cs were randomly distributed into eleven chromosomes of C. praecox. Besides, the quantitative RT-PCR (qPCR) was performed for the expression pattern of several MIKC^C-type genes (CpFUL, CpSEPs and CpAGL6s) in seven bud differentiation stages and indicated that they were involved in dormancy breaking and bud formation. Additionally, overexpression of CpFUL in Arabidopsis Columbia-0 (Col-0) resulted in early flowering and showed difference in floral organs, leaves and fruits. These data could provide conducive information for understanding the roles of MIKC^C-type genes in the floral development and lay a foundation for screening candidate genes to validate function.

The Saururus chinensis genome provides insights into the evolution of pollination strategies and herbaceousness in magnoliids

Saururus chinensis, an herbaceous magnoliid without perianth, represents a clade of early-diverging angiosperms that have gone through woodiness-herbaceousness transition and pollination obstacles: the characteristic white leaves underneath inflorescence during flowering time are considered a substitute for perianth to attract insect pollinators. Here, using the newly sequenced S. chinensis genome, we revisited the phylogenetic position of magnoliids within mesangiosperms, and recovered a sister relationship for magnoliids and Chloranthales. By considering differentially expressed genes, we identified candidate genes that are involved in the morphogenesis of the white leaves in S. chinensis. Among those genes, we verified - in a transgenic experiment with Arabidopsis - that increasing the expression of the "pseudo-etiolation in light" gene (ScPEL) can inhibit the biosynthesis of chlorophyll. ScPEL is thus likely responsible for the switches between green and white leaves, suggesting that changes in gene expression may underlie the evolution of pollination strategies. Despite being an herbaceous plant, S. chinensis still has vascular cambium and maintains the potential for secondary growth as a woody plant, because the necessary machinery, i.e., the entire gene set involved in lignin biosynthesis, is well preserved. However, similar expression levels of two key genes (CCR and CAD) between the stem and other tissues in the lignin biosynthesis pathway are possibly associated with the herbaceous nature of S. chinensis. In conclusion, the S. chinensis genome provides valuable insights into the adaptive evolution of pollination in Saururaceae and reveals a possible mechanism for the evolution of herbaceousness in magnoliids.

Small RNA and Degradome Sequencing in Floral Bud Reveal Roles of miRNAs in Dormancy Release of Chimonanthus praecox

Chimonanthus praecox (wintersweet) is highly valued ornamentally and economically. Floral bud dormancy is an important biological characteristic in the life cycle of wintersweet, and a certain period of chilling accumulation is necessary for breaking floral bud dormancy. Understanding the mechanism of floral bud dormancy release is essential for developing measures against the effects of global warming. miRNAs play important roles in low-temperature regulation of flower bud dormancy through mechanisms that are unclear. In this study, small RNA and degradome sequencing were performed for wintersweet floral buds in dormancy and break stages for the first time. Small RNA sequencing identified 862 known and 402 novel miRNAs; 23 differentially expressed miRNAs (10 known and 13 novel) were screened via comparative analysis of breaking and other dormant floral bud samples. Degradome sequencing identified 1707 target genes of 21 differentially expressed miRNAs. The annotations of the predicted target genes showed that these miRNAs were mainly involved in the regulation of phytohormone metabolism and signal transduction, epigenetic modification, transcription factors, amino acid metabolism, and stress response, etc., during the dormancy release of wintersweet floral buds. These data provide an important foundation for further research on the mechanism of floral bud dormancy in wintersweet.

The genome of Magnolia hypoleuca provides a new insight into cold tolerance and the evolutionary position of magnoliids

Magnolia hypoleuca Sieb. & Zucc, a member of the Magnoliaceae of magnoliids, is one of the most economically valuable, phylogenetic and ornamental tree species in Eastern China. Here, the 1.64 Gb chromosome-level assembly covers 96.64% of the genome which is anchored to 19 chromosomes, with a contig N50 value of 1.71 Mb and 33,873 protein-coding genes was predicted. Phylogenetic analyses between M. hypoleuca and other 10 representative angiosperms suggested that magnoliids were placed as a sister group to the eudicots, rather than sister to monocots or both monocots and eudicots. In addition, the relative timing of the whole-genome duplication (WGD) events about 115.32 Mya for magnoliid plants. M. hypoleuca was found to have a common ancestor with M. officinalis approximately 23.4 MYA, and the climate change of OMT (Oligocene-Miocene transition) is the main reason for the divergence of M. hypoleuca and M. officinalis, which was along with the division of Japanese islands. Moreover, the TPS gene expansion observed in M. hypoleuca might contribute to the enhancement of flower fragrance. Tandem and proximal duplicates of younger age that have been preserved have experienced more rapid sequence divergence and a more clustered distribution on chromosomes contributing to fragrance accumulation, especially phenylpropanoid, monoterpenes and sesquiterpenes and cold tolerance. The stronger selective pressure drived the evolution of tandem and proximal duplicates toward plant self-defense and adaptation. The reference M. hypoleuca genome will provide insights into the evolutionary process of M. hypoleuca and the relationships between the magnoliids with monocots and eudicots, and enable us to delve into the fragrance and cold tolerance produced by M. hypoleuca and provide more robust and deep insight of how the Magnoliales evolved and diversified.

Biogenesis of flavor-related linalool is diverged and genetically conserved in tree peony (Paeonia × suffruticosa)

Floral scent is an important and genetically complex trait in horticultural plants. Tree peony (Paeonia × suffruticosa) originates in the Pan-Himalaya and has nine wild species divided into two subsections, Delavayanae and Vaginatae. Their flowers are beloved worldwide for their sweet floral fragrance, yet the flavor-related volatiles and underlying biosynthetic pathways remain unknown. Here, we characterized the volatile blends of all wild tree peony species and found that the flavor-related volatiles were highly divergent, but linalool was a unique monoterpene in subsect. Delavayanae. Further detection of volatiles in 97 cultivars with various genetic backgrounds showed that linalool was also the characteristic aroma component in Paeonia delavayi hybrid progenies, suggesting that linalool was conserved and dominant within subsect. Delavayanae and its hybrids, instead of species and cultivars from subsect. Vaginatae. Global transcriptome analysis of all wild tree peony species and 60 cultivars revealed five candidate genes that may be involved in key steps of linalool biosynthesis; especially the expressions of three TPS genes, PdTPS1, PdTPS2, and PdTPS4, were significantly positively correlated with linalool emissions across tree peony cultivars. Further biochemical evidence demonstrated that PdTPS1 and PdTPS4 were the pivotal genes determining the species-specific and cultivar-specific emission of linalool. This study revealed a new insight into floral scent divergence in tree peony and would greatly facilitate our understanding of the phylogeny and evolution of Paeonia.

Phylogenetic studies of magnoliids: Advances and perspectives

Magnoliids are the largest flowering plant clades outside of the eudicots and monocots, which are distributed worldwide and have high economic, ornamental and ecological values. Eudicots, monocots and magnoliids are the three major clades of Mesangiospermae, and their phylogenetic relationship is one of the most interesting issues. In recent years, with the continuous accumulation of genomic information, the evolutionary status of magnoliids has become a hot spot in plant phylogenetic research. Although great efforts have been made to study the evolution of magnoliids using molecular data from several representative species such as nuclear genome, plastid genome, mitochondrial genome, and transcriptome, the results of current studies on the phylogenetic status of magnoliids are inconsistent. Here, we systematically describe the current understanding of the molecular research on magnoliid phylogeny and review the differences in the evolutionary state of magnoliids. Understanding the research approaches and limitations of magnoliid phylogeny can guide research strategies to further improve the study of the phylogenetic evolution of magnoliids.

New Insights into the Mechanism of Spatiotemporal Scent Accumulation in Orchid Flowers

Orchid flowers have a unique structure that consists of three sepals and three petals, with one of the petals forming the labellum (lip) that can be differentiated into the hypochile and epichile. In orchids, the emission of floral scent is specific and spatially complex. Little is understood about the molecular and biochemical mechanisms of the differing scent emissions between the parts of orchid flowers. Here, we investigated this in the Cattleya hybrid KOVA, and our study showed that monoterpenes, including linalool and geraniol, are the main components responsible for the KOVA floral scent. The KOVA flower was scentless to the human nose before it reached full bloom, potentially because the 1-deoxy-d-xylulose 5-phosphate synthases (RcDXSs) and 4-hydroxy-3-methylbut-2-enyl diphosphate synthases (RcHDSs) that biosynthesize monoterpenes were highly expressed in flowers only when it reached full flowering. Additionally, the spatial expression profile of the monoterpene synthases (RcMTPSs), which were highly expressed in the basal region of the lip (hypochile), contributed to the highest monoterpene emissions from this part of the flower. This might have caused the hypochile to be more fragrant than the other parts of the flower. These findings enrich our understanding of the difference in scents between different flower parts in plants and provide information to breed novel orchid cultivars with special floral scents.

Creating novel ornamentals via new strategies in the era of genome editing

Ornamental breeding has traditionally focused on improving novelty, yield, quality, and resistance to biotic or abiotic stress. However, achieving these goals has often required laborious crossbreeding, while precise breeding techniques have been underutilized. Fortunately, recent advancements in plant genome sequencing and editing technology have opened up exciting new frontiers for revolutionizing ornamental breeding. In this review, we provide an overview of the current state of ornamental transgenic breeding and propose four promising breeding strategies that have already proven successful in crop breeding and could be adapted for ornamental breeding with the help of genome editing. These strategies include recombination manipulation, haploid inducer creation, clonal seed production, and reverse breeding. We also discuss in detail the research progress, application status, and feasibility of each of these tactics.

The Jasmine (Jasminum sambac) Genome Provides Insight into the Biosynthesis of Flower Fragrances and Jasmonates

Jasminum sambac (jasmine flower), a world-renowned plant appreciated for its exceptional flower fragrance, is of cultural and economic importance. However, the genetic basis of its fragrance is largely unknown. Here, we present the first de novo genome of J. sambac with 550.12 Mb (scaffold N50 = 40.10 Mb) assembled into 13 pseudochromosomes. Terpene synthase genes associated with flower fragrance are significantly amplified in the form of gene clusters through tandem duplications in the genome. Gene clusters within the salicylic acid/benzoic acid/theobromine (SABATH) and BAHD superfamilies were identified as related to the biosynthesis of phenylpropanoid/benzenoid compounds. Several key genes involved in jasmonate biosynthesis were duplicated, causing increased copy numbers. In addition, multi-omics analyses identified various aromatic compounds and many genes involved in fragrance biosynthesis pathways. Furthermore, the roles of JsTPS3 in β-ocimene biosynthesis, as well as JsAOC1 and JsAOS in jasmonic acid biosynthesis, were functionally validated. The genome assembled in this study for J. sambac offers a basic genetic resource for studying floral scent and jasmonate biosynthesis and provides a foundation for functional genomic research and variety improvements in Jasminum.

The Current Developments in Medicinal Plant Genomics Enabled the Diversification of Secondary Metabolites' Biosynthesis

Medicinal plants produce important substrates for their adaptation and defenses against environmental factors and, at the same time, are used for traditional medicine and industrial additives. Plants have relatively little in the way of secondary metabolites via biosynthesis. Recently, the whole-genome sequencing of medicinal plants and the identification of secondary metabolite production were revolutionized by the rapid development and cheap cost of sequencing technology. Advances in functional genomics, such as transcriptomics, proteomics, and metabolomics, pave the way for discoveries in secondary metabolites and related key genes. The multi-omics approaches can offer tremendous insight into the variety, distribution, and development of biosynthetic gene clusters (BGCs). Although many reviews have reported on the plant and medicinal plant genome, chemistry, and pharmacology, there is no review giving a comprehensive report about the medicinal plant genome and multi-omics approaches to study the biosynthesis pathway of secondary metabolites. Here, we introduce the medicinal plant genome and the application of multi-omics tools for identifying genes related to the biosynthesis pathway of secondary metabolites. Moreover, we explore comparative genomics and polyploidy for gene family analysis in medicinal plants. This study promotes medicinal plant genomics, which contributes to the biosynthesis and screening of plant substrates and plant-based drugs and prompts the research efficiency of traditional medicine.

Genome-wide identification and expression of the peroxisome proliferator-activated receptor gene family in the Tibetan highland fish Gymnocypris przewalskii

Peroxisome proliferator-activated receptor (PPAR) plays an important role in the regulation of lipid metabolism and has been widely identified in diverse species. Gymnocypris przewalskii is a native fish of the Qinghai Tibetan Plateau that survives in a chronically cold environment. In the current study, we conducted genome-wide identification of PPAR genes, revealing the existence of seven PPARs in the G. przewalskii genome. Collinearity was observed between two copies of PPARαb and PPARγ in G. przewalskii, suggesting that the additional copy might be gained through whole genome duplication. Both phylogenetic and multiple sequence alignment analyses indicated that PPARs in G. przewalskii were conserved with teleosts. The cold treatment (10 °C and 4 °C) led to the developmental delay of G. przewalskii embryos. Continuous expression of PPARs was observed during the embryonic development of G. przewalskii under normal and cold conditions, with significantly different transcriptional patterns. These results indicated that PPARs participated in the embryonic development of G. przewalskii, and were involved in the cold response during development. The current study proposed a potential role of PPARs in the cold response in the embryonic development of G. przewalskii, which shed light on understanding cold adaptation in Tibetan highland fish.

The genome of Areca catechu provides insights into sex determination of monoecious plants

The areca palm (Areca catechu) has a monoecious spadix, with male flowers on the apical side and females on the basal side. Here, we applied multiomics analysis to investigate sex determination and floral organ development in areca palms. We generated a chromosome-level reference genome of A. catechu with 16 pseudochromosomes, composed of 2.73 Gb and encoding 31 406 genes. Data from RNA-seq and ATAC-seq (assay for transposase accessible chromatin sequencing) suggested that jasmonic acid (JA) synthesis and signal transduction-related genes were differentially expressed between female and male flowers via epigenetic modifications. JA concentration in female flowers was c. 10 times than that in males on the same inflorescence, while JA concentration in hermaphroditic flowers of abnormal inflorescences was about twice that in male flowers of normal inflorescences. JA promotes the development of female flower organs by decreasing the expression of B-function genes, including AGL16, AP3, PIb and PIc. There is also a region on pseudochromosome 15 harboring sex-related genes, including CYP703, LOG, GPAT, AMS and BiP. Among them, CYP703, AMS and BiP were specifically expressed in male flowers.

The chromosome-scale genome of Phoebe bournei reveals contrasting fates of terpene synthase (TPS)-a and TPS-b subfamilies

Terpenoids, including aromatic volatile monoterpenoids and sesquiterpenoids, function in defense against pathogens and herbivores. Phoebe trees are remarkable for their scented wood and decay resistance. Unlike other Lauraceae species investigated to date, Phoebe species predominantly accumulate sesquiterpenoids instead of monoterpenoids. Limited genomic data restrict the elucidation of terpenoid variation and functions. Here, we present a chromosome-scale genome assembly of a Lauraceae tree, Phoebe bournei, and identify 72 full-length terpene synthase (TPS) genes. Genome-level comparison shows pervasive lineage-specific duplication and contraction of TPS subfamilies, which have contributed to the extreme terpenoid variation within Lauraceae species. Although the TPS-a and TPS-b subfamilies were both expanded via tandem duplication in P. bournei, more TPS-a copies were retained and constitutively expressed, whereas more TPS-b copies were lost. The TPS-a genes on chromosome 8 functionally diverged to synthesize eight highly accumulated sesquiterpenes in P. bournei. The essential oil of P. bournei and its main component, β-caryophyllene, exhibited antifungal activities against the three most widespread canker pathogens of trees. The TPS-a and TPS-b subfamilies have experienced contrasting fates over the evolution of P. bournei. The abundant sesquiterpenoids produced by TPS-a proteins contribute to the excellent pathogen resistance of P. bournei trees. Overall, this study sheds light on the evolution and adaptation of terpenoids in Lauraceae and provides valuable resources for boosting plant immunity against pathogens in various trees and crops.

The genome of single-petal jasmine (Jasminum sambac) provides insights into heat stress tolerance and aroma compound biosynthesis

Jasmine [Jasminum sambac (L.) Aiton] is a commercially important cultivated plant species known for its fragrant flowers used in the perfume industry, medicine and cosmetics. In the present study, we obtained a draft genome for the J. sambac cultivar 'Danbanmoli' (JSDB, a single-petal phenotype). We showed that the final genome of J. sambac was 520.80 Mb in size (contig N50 = 145.43 kb; scaffold N50 = 145.53 kb) and comprised 35,363 genes. Our analyses revealed that the J. sambac genome has undergone only an ancient whole-genome duplication (WGD) event. We estimated that the lineage that has given rise to J. sambac diverged from the lineage leading to Osmanthus fragrans and Olea europaea approximately 31.1 million years ago (Mya). On the basis of a combination of genomic and transcriptomic analyses, we identified 92 transcription factors (TFs) and 206 genes related to heat stress response. Base on a combination of genomic, transcriptomic and metabolomic analyses, a range of aroma compounds and genes involved in the benzenoid/phenylpropanoid and terpenoid biosynthesis pathways were identified. In the newly assembled J. sambac genome, we identified a total of 122 MYB, 122 bHLH and 69 WRKY genes. Our assembled J. sambac JSDB genome provides fundamental knowledge to study the molecular mechanism of heat stress tolerance, and improve jasmine flowers and dissect its fragrance.

Natural products of medicinal plants: biosynthesis and bioengineering in post-genomic era

Globally, medicinal plant natural products (PNPs) are a major source of substances used in traditional and modern medicine. As we human race face the tremendous public health challenge posed by emerging infectious diseases, antibiotic resistance and surging drug prices etc., harnessing the healing power of medicinal plants gifted from mother nature is more urgent than ever in helping us survive future challenge in a sustainable way. PNP research efforts in the pre-genomic era focus on discovering bioactive molecules with pharmaceutical activities, and identifying individual genes responsible for biosynthesis. Critically, systemic biological, multi- and inter-disciplinary approaches integrating and interrogating all accessible data from genomics, metabolomics, structural biology, and chemical informatics are necessary to accelerate the full characterization of biosynthetic and regulatory circuitry for producing PNPs in medicinal plants. In this review, we attempt to provide a brief update on the current research of PNPs in medicinal plants by focusing on how different state-of-the-art biotechnologies facilitate their discovery, the molecular basis of their biosynthesis, as well as synthetic biology. Finally, we humbly provide a foresight of the research trend for understanding the biology of medicinal plants in the coming decades.

Integrated volatile metabolomic and transcriptomic analysis provides insights into the regulation of floral scents between two contrasting varieties of Lonicera japonica

Lonicera japonica Thunb., belonging to the Caprifoliaceae family, is an important traditional Chinese medicinal plant. The L. japonica flower (LJF) is widely used in medicine, cosmetics, drinks, and food due to its medicinal and sweet-smelling properties. Considerable efforts have been devoted to investigating the pharmacological activities of LJF; however, the regulatory mechanism of the floral scents remains unknown. We previously selected and bred an elite variety of L. japonica var. chinensis Thunb. called 'Yujin2', which has a strong aroma and is used in functional drinks and cosmetics. In order to reveal the regulatory mechanism of the floral scents of LJF, volatile metabolomic and transcriptomic analyses of the LJF at the silver flowering stage of 'Yujin2' (strong aroma) and 'Fengjin1' (bland odor) were performed. Our results revealed that a total of 153 metabolites and 9,523 genes were differentially regulated in LJF between 'Yujin2' and 'Fengjin1'. The integrated analysis of omics data indicated that the biosynthetic pathways of terpenoids (i.e., monoterpenoids, including geraniol and alpha-terpineol; sesquiterpenoids, including farnesol, farnesal, and alpha-farnesene; triterpenoid squalene), tryptophan and its derivatives (methyl anthranilate), and fatty acid derivatives, were major contributors to the stronger aroma of 'Yujin2' compared to 'Fengjin1'. Moreover, several genes involved in the terpenoid biosynthetic pathway were characterized using quantitative real-time PCR. These results provide insights into the metabolic mechanisms and molecular basis of floral scents in LJF, enabling future screening of genes related to the floral scent regulation, such as alpha-terpineol synthase, geranylgeranyl diphosphate synthase, farnesyl pyrophosphate synthase, anthranilate synthase, as well as transcription factors such as MYB, WRKY, and LFY. The knowledge from this study will facilitate the breeding of quality-improved and more fragrant variety of L. japonica for ornamental purpose and functional beverages and cosmetics.

Comparative transcriptome analysis linked to key volatiles reveals molecular mechanisms of aroma compound biosynthesis in Prunus mume

BACKGROUND

Mei (Prunus mume) is the only woody plant in the genus Prunus with a floral fragrance, but the underlying mechanisms of aroma compound biosynthesis are unclear despite being a matter of considerable interest.

RESULTS

The volatile contents of the petals of two cultivars with significantly different aromas, Prunus mume 'Xiao Lve' and Prunus mume 'Xiangxue Gongfen', were characterised by GC-MS at different flowering periods, and a total of 44 volatile compounds were detected. Among these, the main substances forming the typical aroma of P. mume were identified as eugenol, cinnamyl acetate, hexyl acetate and benzyl acetate, with variations in their relative concentrations leading to sensory differences in the aroma of the two cultivars. We compiled a transcriptome database at key stages of floral fragrance formation in the two cultivars and used it in combination with differential analysis of floral volatiles to construct a regulatory network for the biosynthesis of key aroma compounds. The results indicated that PmPAL enzymes and PmMYB4 transcription factors play important roles in regulating the accumulation of key biosynthetic precursors to these compounds. Cytochrome P450s and short-chain dehydrogenases/reductases might also influence the biosynthesis of benzyl acetate by regulating production of key precursors such as benzaldehyde and benzyl alcohol. Furthermore, by analogy to genes with verified functions in Arabidopsis, we predicted that three PmCAD genes, two 4CL genes, three CCR genes and two IGS genes all make important contributions to the synthesis of cinnamyl acetate and eugenol in P. mume. This analysis also suggested that the downstream genes PmBGLU18-like, PmUGT71A16 and PmUGT73C6 participate in regulation of the matrix-bound and volatile states of P. mume aroma compounds.

CONCLUSIONS

These findings present potential new anchor points for further exploration of floral aroma compound biosynthesis pathways in P. mume, and provide new insights into aroma induction and regulation mechanisms in woody plants.

A Chromosome-Level Genome of the Camphor Tree and the Underlying Genetic and Climatic Factors for Its Top-Geoherbalism

Camphor tree [Cinnamomum camphora (L.) J. Presl], a species in the magnoliid family Lauraceae, is known for its rich volatile oils and is used as a medical cardiotonic and as a scent in many perfumed hygiene products. Here, we present a high-quality chromosome-scale genome of C. camphora with a scaffold N50 of 64.34 Mb and an assembled genome size of 755.41 Mb. Phylogenetic inference revealed that the magnoliids are a sister group to the clade of eudicots and monocots. Comparative genomic analyses identified two rounds of ancient whole-genome duplication (WGD). Tandem duplicated genes exhibited a higher evolutionary rate, a more recent evolutionary history and a more clustered distribution on chromosomes, contributing to the production of secondary metabolites, especially monoterpenes and sesquiterpenes, which are the principal essential oil components. Three-dimensional analyses of the volatile metabolites, gene expression and climate data of samples with the same genotype grown in different locations showed that low temperature and low precipitation during the cold season modulate the expression of genes in the terpenoid biosynthesis pathways, especially TPS genes, which facilitates the accumulation of volatile compounds. Our study lays a theoretical foundation for policy-making regarding the agroforestry applications of camphor tree.

Genome-Wide Identification of Petunia HSF Genes and Potential Function of PhHSF19 in Benzenoid/Phenylpropanoid Biosynthesis

Volatile benzenoids/phenylpropanoids are the main flower scent compounds in petunia (Petunia hybrida). Heat shock factors (HSFs), well known as the main regulator of heat stress response, have been found to be involved in the biosynthesis of benzenoid/phenylpropanoid and other secondary metabolites. In order to figure out the potential function of HSFs in the regulation of floral scent in petunia, we systematically identified the genome-wide petunia HSF genes and analyzed their expression and then the interaction between the key petunia HSF gene with target gene involved in benzenoid/phenylpropanoid biosynthesis. The results revealed that 34 HSF gene family members were obtained in petunia, and most petunia HSFs contained one intron. The phylogenetic analysis showed that 23 petunia HSFs were grouped into the largest subfamily HSFA, while only two petunia HSFs were in HSFC subfamily. The DBD domain and NLS motif were well conserved in most petunia HSFs. Most petunia HSF genes’ promoters contained STRE motifs, the highest number of cis-acting element. PhHSF19 is highly expressed in petal tubes, followed by peduncles and petal limbs. During flower development, the expression level of PhHSF19 was dramatically higher at earlier flower opening stages than that at the bud stage, suggesting that PhHSF19 may have potential roles in regulating benzenoid/phenylpropanoid biosynthesis. The expression pattern of PhHSF19 is positively related with PhPAL2, which catalyzes the first committed step in the phenylpropanoid pathway. In addition, there are three STRE elements in the promoter of PhPAL2. PhHSF19 was proven to positively regulate the expression of PhPAL2 according to the yeast one hybrid and dual luciferase assays. These results lay a theoretical foundation for further studies of the regulation of HSFs on plant flower scent biosynthesis.

Glycosyltransferases: Mining, engineering and applications in biosynthesis of glycosylated plant natural products

UDP-Glycosyltransferases (UGTs) catalyze the transfer of nucleotide-activated sugars to specific acceptors, among which the GT1 family enzymes are well-known for their function in biosynthesis of natural product glycosides. Elucidating GT function represents necessary step in metabolic engineering of aglycone glycosylation to produce drug leads, cosmetics, nutrients and sweeteners. In this review, we systematically summarize the phylogenetic distribution and catalytic diversity of plant GTs. We also discuss recent progress in the identification of novel GT candidates for synthesis of plant natural products (PNPs) using multi-omics technology and deep learning predicted models. We also highlight recent advances in rational design and directed evolution engineering strategies for new or improved GT functions. Finally, we cover recent breakthroughs in the application of GTs for microbial biosynthesis of some representative glycosylated PNPs, including flavonoid glycosides (fisetin 3-O-glycosides, astragalin, scutellarein 7-O-glucoside), terpenoid glycosides (rebaudioside A, ginsenosides) and polyketide glycosides (salidroside, polydatin).

The chromosome-scale genomes of Dipterocarpus turbinatus and Hopea hainanensis (Dipterocarpaceae) provide insights into fragrant oleoresin biosynthesis and hardwood formation

Dipterocarpaceae are typical tropical plants (dipterocarp forests) that are famous for their high economic value because of their production of fragrant oleoresins, top-quality timber and usage in traditional Chinese medicine. Currently, the lack of Dipterocarpaceae genomes has been a limiting factor to decipher the fragrant oleoresin biosynthesis and gain evolutionary insights into high-quality wood formation in Dipterocarpaceae. We generated chromosome-level genome assemblies for two representative Dipterocarpaceae species viz. Dipterocarpus turbinatus Gaertn. f. and Hopea hainanensis Merr. et Chun. Our whole-genome duplication (WGD) analysis revealed that Dipterocarpaceae underwent a shared WGD event, which showed significant impacts on increased copy numbers of genes related to the biosynthesis of terpene, BAHD acyltransferases, fatty acid and benzenoid/phenylpropanoid, which probably confer to the formation of their characteristic fragrant oleoresin. Additionally, compared with common soft wood plants, the expansion of gene families was also found to be associated with wood formation, such as in CESA (cellulose synthase), CSLE (cellulose synthase-like protein E), laccase and peroxidase in Dipterocarpaceae genomes, which might also contribute to the formation of harder, stronger and high-density timbers. Finally, an integrative analysis on a combination of genomic, transcriptomic and metabolic data from different tissues provided further insights into the molecular basis of fragrant oleoresins biosynthesis and high-quality wood formation of Dipterocarpaceae. Our study contributes the first two representative genomes for Dipterocarpaceae, which are valuable genetic resources for further researches on the fragrant oleoresins and superior-quality timber, genome-assisted breeding and improvement, and conservation biology of this family.

Comprehensive Analysis of Endogenous Volatile Compounds, Transcriptome, and Enzyme Activity Reveals PmCAD1 Involved in Cinnamyl Alcohol Synthesis in Prunus mume

Floral scent is an important economic and ornamental trait of Prunus mume. The floral volatiles from most cultivars of P. mume in composition exist significant differences. Cinnamyl alcohol was one of the main floral volatile compounds with distinct abundances in different cultivars, namely, 'Zaohua Lve,' 'Zao Yudie,' 'Fenpi Gongfen,' 'Jiangsha Gongfen,' and 'Fenhong Zhusha.' Based on the determination of endogenous volatiles of full-blooming flowers, vital enzyme activity and transcriptomes were comprehensively analyzed to screen the key potential genes involved in cinnamyl alcohol synthesis. Transcriptome combining with enzyme activity level analysis suggested that the expression levels of three PmCADs were highly correlated with the cinnamyl alcohol dehydrogenase (CAD) enzyme activities in six cultivars. Furthermore, phylogenetic tree and transcriptome analysis suggested that PmCAD1 and PmCAD2 might contribute to the cinnamyl alcohol synthesis. Relative expression analyses and enzyme activity assays showed that PmCAD1 played an important role in cinnamyl alcohol biosynthesis in vitro. Overall, this research lays a theoretical foundation for clarifying comprehensively the molecular biosynthesis mechanism of floral volatiles in P. mume.

MrTPS3 and MrTPS20 Are Responsible for β-Caryophyllene and α-Pinene Production, Respectively, in Red Bayberry (Morella rubra)

Red bayberry is a sweet, tart fruit native to China and grown widely in the south. The key organic compounds forming the distinctive aroma in red bayberry, are terpenoids, mainly β-caryophyllene and α-pinene. However, the key genes responsible for different terpenoids are still unknown. Here, transcriptome analysis on samples from four cultivars, during fruit development, with different terpenoid production, provided candidate genes for volatile organic compound (VOC) production. Terpene synthases (TPS) are key enzymes regulating terpenoid biosynthesis, and 34 TPS family members were identified in the red bayberry genome. MrTPS3 in chromosome 2 and MrTPS20 in chromosome 7 were identified as key genes regulating β-caryophyllene and α-pinene synthesis, respectively, by qRT-PCR. Subcellular localization and enzyme activity assay showed that MrTPS3 was responsible for β-caryophyllene (sesquiterpenes) production and MrTPS20 for α-pinene (monoterpenes). Notably, one amino acid substitution between dark color cultivars and light color cultivars resulted in the loss of function of MrTPS3, causing the different β-caryophyllene production. Our results lay the foundation to study volatile organic compounds (VOCs) in red bayberry and provide potential genes for molecular breeding.

The red flower wintersweet genome provides insights into the evolution of magnoliids and the molecular mechanism for tepal color development

Wintersweet (Chimonanthus praecox) is one of the most important ornamental plants. Its color is mainly determined by the middle tepals. However, the molecular mechanisms underlying the intriguing flower color development among different wintersweet groups are still largely unknown. In addition, wintersweet belongs to magnoliids, and the phylogenetic position of magnoliids remains to be determined conclusively. Here, the whole genome of red flower wintersweet, a new wintersweet type, was sequenced and assembled with high quality. The genome comprised 11 super-scaffolds (chromosomes) with a total size of 737.03 Mb. Based on the analyses of the long branch attraction, incomplete lineage sorting, sparse taxon sampling, and other factors, we suggest that a bifurcating tree may not fully represent the complex early diversification of the angiosperms and that magnoliids are most likely sister to the eudicots. The wintersweet genome appears to have undergone two whole-genome duplication (WGD) events: a recent WGD event representing an independent event specific to the Calycanthaceae and an ancient WGD event shared by Laurales. By integrating genomic, transcriptomic, and metabolomic data, CpANS1 and the transcription factor CpMYB1 were found to play key roles in regulating tepal color development, whereas CpMYB1 needs to form a complex with bHLH and WD40 to fully perform its regulatory function. The present study not only provides novel insights into the evolution of magnoliids and the molecular mechanism for flower color development, but also lays the foundation for subsequent functional genomics study and molecular breeding of wintersweet.

High-quality evergreen azalea genome reveals tandem duplication-facilitated low-altitude adaptability and floral scent evolution

Azalea belongs to Rhododendron, which is one of the largest genera of flowering plants and is well known for the diversity and beauty in its more than 1000 woody species. Rhododendron contains two distinct groups: the most high-altitude and a few low-altitude species; however, the former group is difficult to be domesticated for urban landscaping, and their evolution and adaptation are little known. Rhododendron ovatum has broad adaptation in low-altitude regions but possesses evergreen characteristics like high-altitude species, and it has floral fragrance that is deficient in most cultivars. Here we report the chromosome-level genome assembly of R. ovatum, which has a total length of 549 Mb with scaffold N50 of 41 Mb and contains 41 264 predicted genes. Genomic micro-evolutionary analysis of R. ovatum in comparison with two high-altitude Rhododendron species indicated that the expansion genes in R. ovatum were significantly enriched in defence responses, which may account for its adaptability in low altitudes. The R. ovatum genome contains much more terpene synthase genes (TPSs) compared with the species that lost floral fragrance. The subfamily b members of TPS are involved in the synthesis of sesquiterpenes as well as monoterpenes and play a major role in flora scent biosynthesis and defence responses. Tandem duplication is the primary force driving expansion of defence-responsive genes for extensive adaptability to the low-altitude environments. The R. ovatum genome provides insights into low-altitude adaptation and gain or loss of floral fragrance for Rhododendron species, which are valuable for alpine plant domestication and floral scent breeding.