High-integrity Pueraria montana var. lobata genome and population analysis revealed the genetic diversity of Pueraria genus.

Pueraria montana var. lobata (P. lobata) is a traditional medicinal plant belonging to the Pueraria genus of Fabaceae family. Pueraria montana var. thomsonii (P. thomsonii) and Pueraria montana var. montana (P. montana) are its related species. However, evolutionary history of the Pueraria genus is still largely unknown. Here, a high-integrity, chromosome-level genome of P. lobata and an improved genome of P. thomsonii were reported. It found evidence for an ancient whole-genome triplication and a recent whole-genome duplication shared with Fabaceae in three Pueraria species. Population genomics of 121 Pueraria accessions demonstrated that P. lobata populations had substantially higher genetic diversity, and P. thomsonii was probably derived from P. lobata by domestication as a subspecies. Selection sweep analysis identified candidate genes in P. thomsonii populations associated with the synthesis of auxin and gibberellin, which potentially play a role in the expansion and starch accumulation of tubers in P. thomsonii. Overall, the findings provide new insights into the evolutionary and domestication history of the Pueraria genome and offer a valuable genomic resource for the genetic improvement of these species.

Pan-transcriptomic analysis reveals alternative splicing control of cold tolerance in rice.

Plants have evolved complex mechanisms to adapt to harsh environmental conditions. Rice (Oryza sativa) is a staple food crop that is sensitive to low temperatures. However, its cold stress responses remain poorly understood, thus limiting possibilities for crop engineering to achieve greater cold tolerance. In this study, we constructed a rice pan-transcriptome and characterized its transcriptional regulatory landscape in response to cold stress. We performed Iso-Seq and RNA-Seq of 11 rice cultivars subjected to a time-course cold treatment. Our analyses revealed that alternative splicing-regulated gene expression plays a significant role in the cold stress response. Moreover, we identified CATALASE C (OsCATC) and Os03g0701200 as candidate genes for engineering enhanced cold tolerance. Importantly, we uncovered central roles for the 2 serine-arginine-rich proteins OsRS33 and OsRS2Z38 in cold tolerance. Our analysis of cold tolerance and resequencing data from a diverse collection of 165 rice cultivars suggested that OsRS2Z38 may be a key selection gene in japonica domestication for cold adaptation, associated with the adaptive evolution of rice. This study systematically investigated the distribution, dynamic changes, and regulatory mechanisms of alternative splicing in rice under cold stress. Overall, our work generates a rich resource with broad implications for understanding the genetic basis of cold response mechanisms in plants.

High-quality genome assemblies for two Australimusa bananas (Musa spp.) and insights into regulatory mechanisms of superior fiber properties.

Bananas (Musa spp.) are monocotyledonous plants with high genetic diversity in the Musaceae family that are cultivated mainly in tropical and subtropical countries. The fruits are a popular food, and the plants themselves have diverse uses. Four genetic groups (genomes) are thought to have contributed to current banana cultivars: Musa acuminata (A genome), Musa balbisiana (B genome), Musa schizocarpa (S genome), and species of the Australimusa section (T genome). However, the T genome has not been effectively explored. Here, we present the high-quality TT genomes of two representative accessions, Abaca (Musa textilis), with high-quality natural fiber, and Utafun (Musa troglodytarum, Fe'i group), with abundant ß-carotene. Both the Abaca and Utafun assemblies comprise 10 pseudochromosomes, and their total genome sizes are 613 Mb and 619 Mb, respectively. Comparative genome analysis revealed that the larger size of the T genome is likely attributable to rapid expansion and slow removal of transposons. Compared with those of Musa AA or BB accessions or sisal (Agava sisalana), Abaca fibers exhibit superior mechanical properties, mainly because of their thicker cell walls with a higher content of cellulose, lignin, and hemicellulose. Expression of MusaCesA cellulose synthesis genes peaks earlier in Abaca than in AA or BB accessions during plant development, potentially leading to earlier cellulose accumulation during secondary cell wall formation. The Abaca-specific expressed gene MusaMYB26, which is directly regulated by MusaMYB61, may be an important regulator that promotes precocious expression of secondary cell wall MusaCesAs. Furthermore, MusaWRKY2 and MusaNAC68, which appear to be involved in regulating expression of MusaLAC and MusaCAD, may at least partially explain the high accumulation of lignin in Abaca. This work contributes to a better understanding of banana domestication and the diverse genetic resources in the Musaceae family, thus providing resources for Musa genetic improvement.

Two haplotype-resolved genome assemblies for AAB allotriploid bananas provide insights into banana subgenome asymmetric evolution and Fusarium wilt control.

Bananas (Musa spp.) are one of the world's most important fruit crops and play a vital role in food security for many developing countries. Most banana cultivars are triploids derived from inter- and intraspecific hybridizations between the wild diploid ancestor species Musa acuminate (AA) and M. balbisiana (BB). We report two haplotype-resolved genome assemblies of the representative AAB-cultivated types, Plantain and Silk, and precisely characterize ancestral contributions by examining ancestry mosaics across the genome. Widespread asymmetric evolution is observed in their subgenomes, which can be linked to frequent homologous exchange events. We reveal the genetic makeup of triploid banana cultivars and verify that subgenome B is a rich source of disease resistance genes. Only 58.5% and 59.4% of Plantain and Silk genes, respectively, are present in all three haplotypes, with >50% of genes being differentially expressed alleles in different subgenomes. We observed that the number of upregulated genes in Plantain is significantly higher than that in Silk at one-week post-inoculation with Fusarium wilt tropical race 4 (Foc TR4), which confirms that Plantain can initiate defense responses faster than Silk. Additionally, we compared genomic and transcriptomic differences among the genes related to carotenoid synthesis and starch metabolism between Plantain and Silk. Our study provides resources for better understanding the genomic architecture of cultivated bananas and has important implications for Musa genetics and breeding.

Integrative multiomics profiling of passion fruit reveals the genetic basis for fruit color and aroma.

Passion fruit (Passiflora edulis) possesses a complex aroma and is widely grown in tropical and subtropical areas. Here, we conducted the de novo assembly, annotation, and comparison of PPF (P. edulis Sims) and YPF (P. edulis f. flavicarpa) reference genomes using PacBio, Illumina, and Hi-C technologies. Notably, we discovered evidence of recent whole-genome duplication events in P. edulis genomes. Comparative analysis revealed 7.6∼8.1 million single nucleotide polymorphisms, 1 million insertions/deletions, and over 142 Mb presence/absence variations among different P. edulis genomes. During the ripening of yellow passion fruit, metabolites related to flavor, aroma, and color were substantially accumulated or changed. Through joint analysis of genomic variations, differentially expressed genes, and accumulated metabolites, we explored candidate genes associated with flavor, aroma, and color distinctions. Flavonoid biosynthesis pathways, anthocyanin biosynthesis pathways, and related metabolites are pivotal factors affecting the coloration of passion fruit, and terpenoid metabolites accumulated more in PPF. Finally, by heterologous expression in yeast (Saccharomyces cerevisiae), we functionally characterized 12 terpene synthases. Our findings revealed that certain TPS homologs in both YPF and PPF varieties produce identical terpene products, while others yield distinct compounds or even lose their functionality. These discoveries revealed the genetic and metabolic basis of unique characteristics in aroma and flavor between the 2 passion fruit varieties. This study provides resources for better understanding the genome architecture and accelerating genetic improvement of passion fruits.

Telomere-to-telomere assembly of cassava genome reveals the evolution of cassava and divergence of allelic expression.

Cassava is a crucial crop that makes a significant contribution to ensuring human food security. However, high-quality telomere-to-telomere cassava genomes have not been available up to now, which has restricted the progress of haploid molecular breeding for cassava. In this study, we constructed two nearly complete haploid resolved genomes and an integrated, telomere-to-telomere gap-free reference genome of an excellent cassava variety, 'Xinxuan 048', thereby providing a new high-quality genomic resource. Furthermore, the evolutionary history of several species within the Euphorbiaceae family was revealed. Through comparative analysis of haploid genomes, it was found that two haploid genomes had extensive differences in linear structure, transcriptome features, and epigenetic characteristics. Genes located within the highly divergent regions and differentially expressed alleles are enriched in the functions of auxin response and the starch synthesis pathway. The high heterozygosity of cassava 'Xinxuan 048' leads to rapid trait segregation in the first selfed generation. This study provides a theoretical basis and genomic resource for molecular breeding of cassava haploids.

Graph-based pan-genomes: increased opportunities in plant genomics.

Due to the development of sequencing technology and the great reduction in sequencing costs, an increasing number of plant genomes have been assembled, and numerous genomes have revealed large amounts of variations. However, a single reference genome does not allow the exploration of species diversity, and therefore the concept of pan-genome was developed. A pan-genome is a collection of all sequences available for a species, including a large number of consensus sequences, large structural variations, and small variations including single nucleotide polymorphisms and insertions/deletions. A simple linear pan-genome does not allow these structural variations to be intuitively characterized, so graph-based pan-genomes have been developed. These pan-genomes store sequence and structural variation information in the form of nodes and paths to store and display species variation information in a more intuitive manner. The key role of graph-based pan-genomes is to expand the coordinate system of the linear reference genome to accommodate more regions of genetic diversity. Here, we review the origin and development of graph-based pan-genomes, explore their application in plant research, and further highlight the application of graph-based pan-genomes for future plant breeding.

Structure and Physical Properties of the Layered Titanium-Based Pnictide Oxides (EuF)2Ti2Pn2O (Pn = Sb, Bi).

We report two novel titanium-based pnictide oxide compounds (EuF)2Ti2Pn2O (Pn = Sb, Bi), which are synthesized by replacing Sr2+ in (SrF)2Ti2Pn2O [Liu, R. H. Structure and Physical Properties of the Layered Pnictide-Oxides: (SrF)2Ti2Pn2O (Pn = As, Sb) and (SmO)2Ti2Sb2O. Chem. Mater. 2010, 22, 1503-1508] with Eu2+ using a solid-state reaction. (EuF)2Ti2Sb2O exhibits an obvious anomaly in resistivity and heat capacity at T ∼ 195 K, which may arise from the spin-density wave/charge-density wave instability. Similar features are also observed in BaTi2Pn2O, (SrF)2Ti2Pn2O, and Na2Ti2Pn2O (Pn = As and Sb) [Liu, R. H. Structure and Physical Properties of the Layered Pnictide-Oxides: (SrF)2Ti2Pn2O (Pn = As, Sb) and (SmO)2Ti2Sb2O. Chem. Mater. 2010, 22, 1503-1508, Ozawa, T. C. Chemistry of layered d-metal pnictide oxides and their potential as candidates for new superconductors. Sci. Technol. Adv. Mater. 2008, 9, 033003, Wang, X. F. Structure and physical properties for a new layered pnictide-oxide: BaTi2As2O. J. Phys.: Condens. Matter. 2010, 22, 075702, and Xu, H. C. Electronic structure of the BaTi2As2O parent compound of the titanium-based oxypnictide superconductor. Phys. Rev. B 2014, 89, 155108]. Magnetic susceptibility measurements indicate an antiferromagnetic transition at T ∼ 2.5 K for (EuF)2Ti2Sb2O. In particular, the electronic specific heat coefficients of both (EuF)2Ti2Sb2O and (EuF)2Ti2Bi2O are significantly enhanced compared to those of (SrF)2Ti2Pn2O, Na2Ti2Pn2O, and BaTi2Pn2O,1,5,6 which may be due to a strong electron correlation effect in this system. Thus, (EuF)2Ti2Pn2O (Pn = Sb, Bi) may provide new platforms for studying density wave, magnetic ordering, and electron correlation effects.

A Chromosome Level Genome Assembly of a Winter Turnip Rape (Brassica rapa L.) to Explore the Genetic Basis of Cold Tolerance.

Winter rapeseed (Brassica rapa L.) is an important overwintering oilseed crop that is widely planted in northwest China and suffers chronic low temperatures in winter. So the cold stress becomes one of the major constraints that limit its production. The currently existing genomes limit the understanding of the cold-tolerant genetic basis of rapeseed. Here we assembled a high-quality long-read genome of B. rapa "Longyou-7" cultivar, which has a cold-tolerant phenotype, and constructed a graph-based pan-genome to detect the structural variations within homologs of currently reported cold-tolerant related genes in the "Longyou-7" genome, which provides an additional elucidation of the cold-tolerant genetic basis of "Longyou-7" cultivar and promotes the development of cold-tolerant breeding in B. rapa.

Oil plant genomes: current state of the science.

Vegetable oils are an indispensable nutritional component of the human diet as well as important raw materials for a variety of industrial applications such as pharmaceuticals, cosmetics, oleochemicals, and biofuels. Oil plant genomes are highly diverse, and their genetic variation leads to a diversity in oil biosynthesis and accumulation along with agronomic traits. This review discusses plant oil biosynthetic pathways, current state of genome assembly, polyploidy and asymmetric evolution of genomes of oil plants and their wild relatives, and research progress of pan-genomics in oil plants. The availability of complete high-resolution genomes and pan-genomes has enabled the identification of structural variations in the genomes that are associated with the diversity of agronomic and environment fitness traits. These and future genomes also provide powerful tools to understand crop evolution and to harvest the rich natural variations to improve oil crops for enhanced productivity, oil quality, and adaptability to changing environments.

High-quality reference genome sequences of two coconut cultivars provide insights into evolution of monocot chromosomes and differentiation of fiber content and plant height.

BACKGROUND: Coconut is an important tropical oil and fruit crop whose evolutionary position renders it a fantastic species for the investigation of the evolution of monocot chromosomes and the subsequent differentiation of ancient plants. RESULTS: Here, we report the assembly and annotation of reference-grade genomes of Cn. tall and Cn. dwarf, whose genome sizes are 2.40 Gb and 2.39 Gb, respectively. The comparative analysis reveals that the two coconut subspecies diverge about 2-8 Mya while the conserved Arecaceae-specific whole-genome duplication (ω WGD) occurs approximately 47-53 Mya. It additionally allows us to reconstruct the ancestral karyotypes of the ten ancient monocot chromosomes and the evolutionary trajectories of the 16 modern coconut chromosomes. Fiber synthesis genes in Cn. tall, related to lignin and cellulose synthesis, are found at a higher copy number and expression level than dwarf coconuts. Integrated multi-omics analysis reveals that the difference in coconut plant height is the result of altered gibberellin metabolism, with both the GA20ox copy number and a single-nucleotide change in the promoter together leading to the difference in plant height between Cn. tall and Cn. dwarf. CONCLUSION: We provide high-quality coconut genomes and reveal the genetic basis of trait differences between two coconuts through multi-omics analysis. We also reveal that the selection of plant height has been targeted for the same gene for millions of years, not only in natural selection of ancient plant as illustrated in coconut, but also for artificial selection in cultivated crops such as rice and maize.

Two gap-free reference genomes and a global view of the centromere architecture in rice.

Rice (Oryza sativa), a major staple throughout the world and a model system for plant genomics and breeding, was the first crop genome sequenced almost two decades ago. However, reference genomes for all higher organisms to date contain gaps and missing sequences. Here, we report the assembly and analysis of gap-free reference genome sequences for two elite O. sativa xian/indica rice varieties, Zhenshan 97 and Minghui 63, which are being used as a model system for studying heterosis and yield. Gap-free reference genomes provide the opportunity for a global view of the structure and function of centromeres. We show that all rice centromeric regions share conserved centromere-specific satellite motifs with different copy numbers and structures. In addition, the similarity of CentO repeats in the same chromosome is higher than across chromosomes, supporting a model of local expansion and homogenization. Both genomes have over 395 non-TE genes located in centromere regions, of which ∼41% are actively transcribed. Two large structural variants at the end of chromosome 11 affect the copy number of resistance genes between the two genomes. The availability of the two gap-free genomes lays a solid foundation for further understanding genome structure and function in plants and breeding climate-resilient varieties.

Analysis of Rice Transcriptome Reveals the LncRNA/CircRNA Regulation in Tissue Development.

BACKGROUND: Long non-coding RNAs (lncRNAs) and circular RNAs (circRNAs) can play important roles in many biological processes. However, no study of the influence of epigenetics factors or the 3D structure of the genome in their regulation is available in plants. RESULTS: In the current analysis, we identified a total of 15,122 lncRNAs and 7902 circRNAs in three tissues (root, leaf and panicle) in the rice varieties Minghui 63, Zhenshan 97 and their hybrid Shanyou 63. More than 73% of these lncRNAs and parental genes of circRNAs (P-circRNAs) are shared among Oryza sativa with high expression specificity. We found that, compared with protein-coding genes, the loci of these lncRNAs have higher methylation levels and the loci of circRNAs tend to locate in the middle of genes with high CG and CHG methylation. Meanwhile, the activated lncRNAs and P-circRNAs are mainly transcribed from demethylated regions containing CHH methylation. In addition, ~ 53% lncRNAs and ~ 15% P-circRNAs are associated with transposable elements (TEs), especially miniature inverted-repeat transposable elements and RC/Helitron. We didn't find correlation between the expression of lncRNAs and histone modifications; however, we found that the binding strength and interaction of RNAPII significantly affects lncRNA expression. Interestingly, P-circRNAs tend to combine active histone modifications. Finally, we found that lncRNAs and circRNAs acting as competing-endogenous RNAs have the potential to regulate the expression of genes, such as osa-156 l-5p (related to yield) and osa-miR444a-3p (related to N/P metabolism) confirmed through dual-luciferase reporter assays, with important roles in the growth and development of rice, laying a foundation for future rice breeding analyses. CONCLUSIONS: In conclusion, our study comprehensively analyzed the important regulatory roles of lncRNA/circRNA in the tissue development of Indica rice from multiple perspectives.

Long-read sequencing reveals widespread intragenic structural variants in a recent allopolyploid crop plant.

Genome structural variation (SV) contributes strongly to trait variation in eukaryotic species and may have an even higher functional significance than single-nucleotide polymorphism (SNP). In recent years, there have been a number of studies associating large chromosomal scale SV ranging from hundreds of kilobases all the way up to a few megabases to key agronomic traits in plant genomes. However, there have been little or no efforts towards cataloguing small- (30-10 000 bp) to mid-scale (10 000-30 000 bp) SV and their impact on evolution and adaptation-related traits in plants. This might be attributed to complex and highly duplicated nature of plant genomes, which makes them difficult to assess using high-throughput genome screening methods. Here, we describe how long-read sequencing technologies can overcome this problem, revealing a surprisingly high level of widespread, small- to mid-scale SV in a major allopolyploid crop species, Brassica napus. We found that up to 10% of all genes were affected by small- to mid-scale SV events. Nearly half of these SV events ranged between 100 bp and 1000 bp, which makes them challenging to detect using short-read Illumina sequencing. Examples demonstrating the contribution of such SV towards eco-geographical adaptation and disease resistance in oilseed rape suggest that revisiting complex plant genomes using medium-coverage long-read sequencing might reveal unexpected levels of functional gene variation, with major implications for trait regulation and crop improvement.

The genome of jojoba (Simmondsia chinensis): A taxonomically isolated species that directs wax ester accumulation in its seeds.

Seeds of the desert shrub, jojoba (Simmondsia chinensis), are an abundant, renewable source of liquid wax esters, which are valued additives in cosmetic products and industrial lubricants. Jojoba is relegated to its own taxonomic family, and there is little genetic information available to elucidate its phylogeny. Here, we report the high-quality, 887-Mb genome of jojoba assembled into 26 chromosomes with 23,490 protein-coding genes. The jojoba genome has only the whole-genome triplication (γ) shared among eudicots and no recent duplications. These genomic resources coupled with extensive transcriptome, proteome, and lipidome data helped to define heterogeneous pathways and machinery for lipid synthesis and storage, provided missing evolutionary history information for this taxonomically segregated dioecious plant species, and will support efforts to improve the agronomic properties of jojoba.

Eight high-quality genomes reveal pan-genome architecture and ecotype differentiation of Brassica napus.

Rapeseed (Brassica napus) is the second most important oilseed crop in the world but the genetic diversity underlying its massive phenotypic variations remains largely unexplored. Here, we report the sequencing, de novo assembly and annotation of eight B. napus accessions. Using pan-genome comparative analysis, millions of small variations and 77.2-149.6 megabase presence and absence variations (PAVs) were identified. More than 9.4% of the genes contained large-effect mutations or structural variations. PAV-based genome-wide association study (PAV-GWAS) directly identified causal structural variations for silique length, seed weight and flowering time in a nested association mapping population with ZS11 (reference line) as the donor, which were not detected by single-nucleotide polymorphisms-based GWAS (SNP-GWAS), demonstrating that PAV-GWAS was complementary to SNP-GWAS in identifying associations to traits. Further analysis showed that PAVs in three FLOWERING LOCUS C genes were closely related to flowering time and ecotype differentiation. This study provides resources to support a better understanding of the genome architecture and acceleration of the genetic improvement of B. napus.

Analyzing AbrB-Knockout Effects through Genome and Transcriptome Sequencing of Bacillus licheniformis DW2.

As an industrial bacterium, Bacillus licheniformis DW2 produces bacitracin which is an important antibiotic for many pathogenic microorganisms. Our previous study showed AbrB-knockout could significantly increase the production of bacitracin. Accordingly, it was meaningful to understand its genome features, expression differences between wild and AbrB-knockout (ΔAbrB) strains, and the regulation of bacitracin biosynthesis. Here, we sequenced, de novo assembled and annotated its genome, and also sequenced the transcriptomes in three growth phases. The genome of DW2 contained a DNA molecule of 4,468,952 bp with 45.93% GC content and 4,717 protein coding genes. The transcriptome reads were mapped to the assembled genome, and obtained 4,102∼4,536 expressed genes from different samples. We investigated transcription changes in B. licheniformis DW2 and showed that ΔAbrB caused hundreds of genes up-regulation and down-regulation in different growth phases. We identified a complete bacitracin synthetase gene cluster, including the location and length of bacABC, bcrABC, and bacT, as well as their arrangement. The gene cluster bcrABC were significantly up-regulated in ΔAbrB strain, which supported the hypothesis in previous study of bcrABC transporting bacitracin out of the cell to avoid self-intoxication, and was consistent with the previous experimental result that ΔAbrB could yield more bacitracin. This study provided a high quality reference genome for B. licheniformis DW2, and the transcriptome data depicted global alterations across two strains and three phases offered an understanding of AbrB regulation and bacitracin biosynthesis through gene expression.