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Asset Tag: Plant genome

July 7, 2019  |  

Towards integration of population and comparative genomics in forest trees.

The past decade saw the initiation of an ongoing revolution in sequencing technologies that is transforming all fields of biology. This has been driven by the advent and widespread availability of high-throughput, massively parallel short-read sequencing (MPS) platforms. These technologies have enabled previously unimaginable studies, including draft assemblies of the massive genomes of coniferous species and population-scale resequencing. Transcriptomics studies have likewise been transformed, with RNA-sequencing enabling studies in nonmodel organisms, the discovery of previously unannotated genes (novel transcripts), entirely new classes of RNAs and previously unknown regulatory mechanisms. Here we touch upon current developments in the areas of genome assembly, comparative regulomics and population genetics as they relate to studies of forest tree species.© 2016 The Authors. New Phytologist © 2016 New Phytologist Trust.

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July 7, 2019  |  

The mechanisms whereby the green alga Chlorella ohadii, isolated from desert soil crust, exhibits unparalleled photodamage resistance.

Excess illumination damages the photosynthetic apparatus with severe implications with regard to plant productivity. Unlike model organisms, the growth of Chlorella ohadii, isolated from desert soil crust, remains unchanged and photosynthetic O2 evolution increases, even when exposed to irradiation twice that of maximal sunlight. Spectroscopic, biochemical and molecular approaches were applied to uncover the mechanisms involved. D1 protein in photosystem II (PSII) is barely degraded, even when exposed to antibiotics that prevent its replenishment. Measurements of various PSII parameters indicate that this complex functions differently from that in model organisms and suggest that C. ohadii activates a nonradiative electron recombination route which minimizes singlet oxygen formation and the resulting photoinhibition. The light-harvesting antenna is very small and carotene composition is hardly affected by excess illumination. Instead of succumbing to photodamage, C. ohadii activates additional means to dissipate excess light energy. It undergoes major structural, compositional and physiological changes, leading to a large rise in photosynthetic rate, lipids and carbohydrate content and inorganic carbon cycling. The ability of C. ohadii to avoid photodamage relies on a modified function of PSII and the dissipation of excess reductants downstream of the photosynthetic reaction centers. The biotechnological potential as a gene source for crop plant improvement is self-evident.© 2016 The Authors. New Phytologist © 2016 New Phytologist Trust.

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July 7, 2019  |  

Assembly of the draft genome of buckwheat and its applications in identifying agronomically useful genes.

Buckwheat (Fagopyrum esculentum Moench; 2n = 2x = 16) is a nutritionally dense annual crop widely grown in temperate zones. To accelerate molecular breeding programmes of this important crop, we generated a draft assembly of the buckwheat genome using short reads obtained by next-generation sequencing (NGS), and constructed the Buckwheat Genome DataBase. After assembling short reads, we determined 387,594 scaffolds as the draft genome sequence (FES_r1.0). The total length of FES_r1.0 was 1,177,687,305 bp, and the N50 of the scaffolds was 25,109 bp. Gene prediction analysis revealed 286,768 coding sequences (CDSs; FES_r1.0_cds) including those related to transposable elements. The total length of FES_r1.0_cds was 212,917,911 bp, and the N50 was 1,101 bp. Of these, the functions of 35,816 CDSs excluding those for transposable elements were annotated by BLAST analysis. To demonstrate the utility of the database, we conducted several test analyses using BLAST and keyword searches. Furthermore, we used the draft genome as a reference sequence for NGS-based markers, and successfully identified novel candidate genes controlling heteromorphic self-incompatibility of buckwheat. The database and draft genome sequence provide a valuable resource that can be used in efforts to develop buckwheat cultivars with superior agronomic traits.© The Author 2016. Published by Oxford University Press on behalf of Kazusa DNA Research Institute.

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July 7, 2019  |  

Exploiting next-generation sequencing to solve the haplotyping puzzle in polyploids: a simulation study.

Haplotypes are the units of inheritance in an organism, and many genetic analyses depend on their precise determination. Methods for haplotyping single individuals use the phasing information available in next-generation sequencing reads, by matching overlapping single-nucleotide polymorphisms while penalizing post hoc nucleotide corrections made. Haplotyping diploids is relatively easy, but the complexity of the problem increases drastically for polyploid genomes, which are found in both model organisms and in economically relevant plant and animal species. Although a number of tools are available for haplotyping polyploids, the effects of the genomic makeup and the sequencing strategy followed on the accuracy of these methods have hitherto not been thoroughly evaluated.We developed the simulation pipeline haplosim to evaluate the performance of three haplotype estimation algorithms for polyploids: HapCompass, HapTree and SDhaP, in settings varying in sequencing approach, ploidy levels and genomic diversity, using tetraploid potato as the model. Our results show that sequencing depth is the major determinant of haplotype estimation quality, that 1?kb PacBio circular consensus sequencing reads and Illumina reads with large insert-sizes are competitive and that all methods fail to produce good haplotypes when ploidy levels increase. Comparing the three methods, HapTree produces the most accurate estimates, but also consumes the most resources. There is clearly room for improvement in polyploid haplotyping algorithms.

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July 7, 2019  |  

Current advances in genome sequencing of common wheat and its ancestral species

Common wheat is an important and widely cultivated food crop throughout the world. Much progress has been made in regard to wheat genome sequencing in the last decade. Starting from the sequencing of single chromosomes/chromosome arms whole genome sequences of common wheat and its diploid and tetraploid ancestors have been decoded along with the development of sequencing and assembling technologies. In this review, we give a brief summary on international progress in wheat genome sequencing, and mainly focus on reviewing the effort and contributions made by Chinese scientists.

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July 7, 2019  |  

A comprehensive model of DNA fragmentation for the preservation of High Molecular Weight DNA

During DNA extraction the DNA molecule undergoes physical and chemical shearing, causing the DNA to fragment into shorter and shorter pieces. Under common laboratory conditions this fragmentation yields DNA fragments of 5-35 kilobases (kb) in length. This fragment length is more than sufficient for DNA sequencing using short-read technologies which generate reads 50-600 bp in length, but insufficient for long-read sequencing and linked reads where fragment lengths of more than 40 kb may be desirable. This study provides a theoretical framework for quality management to ensure access to high molecular weight DNA in samples. Shearing can be divided into physical and chemical shearing which generate different patterns of fragmentation. Exposure to physical shearing creates a characteristic fragment length where DNA fragments are cut in half by shear stress. This characteristic length can be measured using gel electrophoresis or instruments for DNA fragment analysis. Chemical shearing generates randomly distributed fragment lengths visible as a smear of DNA below the peak fragment length. By measuring the peak of DNA fragment length and the proportion of very short DNA fragments both sources of shearing can be measured using commonly used laboratory techniques, providing a suitable quantification of DNA integrity of DNA for sequencing with long-read technologies.

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July 7, 2019  |  

Identification and expression analysis of wheat TaGF14 genes.

The 14-3-3 gene family members play key roles in various cellular processes. However, little is known about the numbers and roles of 14-3-3 genes in wheat. The aims of this study were to identify TaGF14 numbers in wheat by searching its whole genome through blast, to study the phylogenetic relationships with other plant species and to discuss the functions of TaGF14s. The results showed that common wheat harbored 20 TaGF14 genes, located on wheat chromosome groups 2, 3, 4, and 7. Out of them, eighteen TaGF14s are non-e proteins, and two wheat TaGF14 genes, TaGF14i and TaGF14f, are e proteins. Phylogenetic analysis indicated that these genes were divided into six clusters: cluster 1 (TaGF14d, TaGF14g, TaGF14j, TaGF14h, TaGF14c, and TaGF14n); cluster 2 (TaGF14k); cluster 3 (TaGF14b, TaGF14l, TaGF14m, and TaGF14s); cluster 4 (TaGF14a, TaGF14e, and TaGF14r); cluster 5 (TaGF14i and TaGF14f); and cluster 6 (TaGF14o, TaGF14p, TaGF14q, and TaGF14t). Tissue-specific gene expressions suggested that all TaGF14s were likely constitutively expressed, except two genes, i.e., TaGF14p and TaGF14f. And the highest amount of TaGF14 transcripts were observed in developing grains at 20 days post anthesis (DPA), especially for TaGF14j and TaGF14l. After drought stress, five genes, i.e., TaGF14c, TaGF14d, TaGF14g, TaGF14h, and TaGF14j, were up-regulated expression under drought stress for both 1 and 6 h, suggesting these genes played vital role in combating against drought stress. However, all the TaGF14s were down-regulated expression under heat stress for both 1 and 6 h, indicating TaGF14s may be negatively associated with heat stress by reducing the expression to combat heat stress or through other pathways. These results suggested that cluster 1, e.g., TaGF14j, may participate in the whole wheat developing stages, e.g., grain-filling (starch biosynthesis) and may also participate in combating against drought stress. Subsequently, a homolog of TaGF14j, TaGF14-JM22, were cloned by RACE and used to validate its function. Immunoblotting results showed that TaGF14-JM22 protein, closely related to TaGF14d, TaGF14g, and TaGF14j, can interact with AGP-L, SSI, SSII, SBEIIa, and SBEIIb in developing grains, suggesting that TaGF14s located on group 4 may be involved in starch biosynthesis. Therefore, it is possible to develop starch-rich wheat cultivars by modifying TaGF14s.

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July 7, 2019  |  

Oryza rufipogon Griff.

Oryza rufipogon, the progenitor of present-day cultivated rice, O. sativa, is one of the most studied wild species of rice. It is a perennial plant commonly found in a marsh or aquatic habitats of eastern and southern Asia. It has partial outcrossing behavior and is photoperiod sensitive. The flowering time usually ranges between September and November. It has been and is being exploited as a source of valuable genes and QTLs for yield components as well as resistance against biotic and abiotic stresses. A number of populations like chromosome segment substitution lines, backcross inbred lines, near-isogenic lines, and recombinant inbred lines have been developed from crosses between O. rufipogon and O. sativa as a prebreeding resource. These are being employed for broadening the genetic base of cultivated rice and diversify the breeder’s pool. With the advent of sequencing technologies, a number of phylogenetic studies have been conducted to reveal the evolutionary relationship of O. rufipogon with cultivated rice O. sativa. Further, transcriptomic studies characterizing the effect of various abiotic stresses have been conducted on this wild species. Role of miRNA under stress reaction has also been studied. Though the genetic, genomic, and transcriptomic resources are abundant, the proteomic resources for O. rufipogon are limited.

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July 7, 2019  |  

Oryza meridionalis NQ Ng

Oryza meridionalis is an AA genome species found in Northern Australia. Phylogenetic analysis places this as the most distant of the AA genome species from domesticated rice (Oryza sativa). This makes it a key genetic resource for rice improvement. A draft nuclear genome sequence is available, and also the chloroplast genome has been sequenced from many genotypes. The high amylose starch content in these taxa may be useful for developing new rice grain characteristics. Here we have reviewed the all the research advancements that are made till today on this species.

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July 7, 2019  |  

Oryza glaberrima Steud.

Oryza glaberrima is the African cultivated rice species, domesticated from its wild ancestor by farmers living in Inland Delta of Niger River. Several studies indicated that it has extremely narrow genetic diversity compared to both its wild progenitor, Oryza barthii and the Asian rice, Oryza sativa which can mainly be attributed to a severe domestication bottleneck. Despite its scarcity in farmer’s field due to its low yield potential, high shattering and lodging susceptibility, O. glaberrima is of great value not only to Africa but also globally. Perhaps its greatest contribution to regional and global food security is as a source of genes, as it possesses resistance/tolerance to various biotic and abiotic stresses. It also has unique starch-related traits which give it good cooking and eating properties. Advances in DNA sequencing have provided useful genomic resources for African rice, key among them being whole genome sequences. Genomic tools are enabling greater understanding of the useful functional diversity found in this species. These advances have potential of addressing some of the undesirable attributes found in this species which have led to its continued replacement by Asian rice. Development of new generation of rice varieties for African farmers will therefore require the adoption of advanced molecular breeding tools as these will allow efficient utilization of the wealth and resilience found in African rice in rice improvement.

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July 7, 2019  |  

Natural rubber and the Russian dandelion genome

The world needs rubber. Rubber is crucial for the tires on the cars, trucks and airplanes that propel modern transportation. It is equally important for daily tasks: latex gloves in the lab, balloons in angioplasty and wetsuits that warm a cold dip in the ocean. Rubber can be made synthetically from petroleum derivatives, but synthetic rubber is not as strong as rubber iso- lated from plants. The principal plant source for natural rubber (NR) is the sap of the Par´ a tree (Hevea brasiliensis), which is grown throughout Southeast Asia. Unfortunately, the produc- tion capacity of the Par´ a tree is limited by the availability of suitable land and by labor-intensive harvesting methods. The sustainability of the Par´ a crop is also constrained by its narrow genetic base, which may make the crop susceptible to disease.

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July 7, 2019  |  

Rooting for new sources of natural rubber

Global production of natural rubber (NR) depends overwhelmingly on the Pará rubber tree (Hevea brasiliensis), a slow-growing tropical tree that is threatened by low genetic diversity and high susceptibility to fungal blight [1]. Alternative rubber sources have been sought for more than a century, but very few species have been found that produce rubber of comparable quality [2]. One of the brightest candidates, first noticed by breeders in Soviet-era Russia, is Taraxacum kok-saghyz (commonly called TKS). This close relative of the common weedy dandelion has a number of attractive features. As a native of central Asia, TKS can be cultivated as a hardy, annual field crop in temperate climates. Its natural latex, produced at highest levels in the roots, yields a high-molecular-weight NR that is chemically similar to the rubber tree and far superior to synthetic rubber. And, as an added bonus, TKS produces inulin, a dietary fiber and low-glycemic-index sweetener that can be fermented for industrial bioethanol production. What TKS has lacked—until now—is an assembled reference genome that could be used for genome-enabled crop improvement and elucidation of the pathways for rubber and inulin biosynthesis. In their paper published in this issue, Jiayang Li, Hong Yu and colleagues [3] have taken a major step in rectifying that problem.

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July 7, 2019  |  

Sustaining global agriculture through rapid detection and deployment of genetic resistance to deadly crop diseases.

Contents Summary 45 I. Introduction 45 II. Targeted chromosome-based cloning via long-range assembly (TACCA) 46 III. Resistance gene cloning through mutational mapping (MutMap) 47 IV. Cloning through mutant chromosome sequencing (MutChromSeq) 47 V. Rapid cloning through resistance gene enrichment and sequencing (RenSeq) 49 VI. Cloning resistance genes through transcriptome profiling (RNAseq) 49 VII. Resistance gene deployment strategies 49 VIII. Conclusions 50 Acknowledgements 50 References 50 SUMMARY: Genetically encoded resistance is a major component of crop disease management. Historically, gene loci conferring resistance to pathogens have been identified through classical genetic methods. In recent years, accelerated gene cloning strategies have become available through advances in sequencing, gene capture and strategies for reducing genome complexity. Here, I describe these approaches with key emphasis on the isolation of resistance genes to the cereal crop diseases that are an ongoing threat to global food security. Rapid gene isolation enables their efficient deployment through marker-assisted selection and transgenic technology. Together with innovations in genome editing and progress in pathogen virulence studies, this creates further opportunities to engineer long-lasting resistance. These approaches will speed progress towards a future of farming using fewer pesticides.© 2017 Commonwealth of Australia. New Phytologist © 2017 New Phytologist Trust.

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July 7, 2019  |  

Correction of persistent errors in arabidopsis reference mitochondrial genomes.

Arabidopsis thaliana remains the foremost model system for plant genetics and genomics, and researchers rely on the accuracy of its genomic resources. The first completely sequenced angiosperm mitochondrial genome was obtained from Arabidopsis C24 (Unseld et al., 1997), and more recent efforts have produced additional Arabidopsis reference genomes, including one for Col-0, the most widely used ecotype in plant genetic research (Davila et al., 2011). These studies were based on older DNA sequencing methods, making them subject to errors associated with lower levels of sequencing coverage or the extremely short read lengths produced by early-generation Illumina technologies. Indeed, although the more recently published Arabidopsis mitochondrial reference genome sequences made substantial progress in improving upon earlier versions, they still have high error rates. By comparing publicly available Illumina sequence data to the Arabidopsis Col-0 reference genome, we found that it contains a sequence error every 2.4 kb on average, including 57 single-nucleotide polymorphisms (SNPs), 96 indels (up to 901 bp in size), and a large repeat-mediated rearrangement. Most of these errors appear to have been carried over from the original Arabidopsis mitochondrial genome sequence by reference-based assembly approaches, which has misled subsequent studies of plant mitochondrial mutation and molecular evolution by giving the false impression that the errors are naturally occurring variants present in multiple ecotypes. Building on the progress made by previous researchers, we provide a corrected reference sequence that we hope will serve as a useful community resource for future investigations in the field of plant mitochondrial genetics.

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