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1.
Engineering salinity tolerance in plants: progress and prospects.
Wani, SH, Kumar, V, Khare, T, Guddimalli, R, Parveda, M, Solymosi, K, Suprasanna, P, Kavi Kishor, PB
Planta. 2020;(4):76
Abstract
There is a need to integrate conceptual framework based on the current understanding of salt stress responses with different approaches for manipulating and improving salt tolerance in crop plants. Soil salinity exerts significant constraints on global crop production, posing a serious challenge for plant breeders and biotechnologists. The classical transgenic approach for enhancing salinity tolerance in plants revolves by boosting endogenous defence mechanisms, often via a single-gene approach, and usually involves the enhanced synthesis of compatible osmolytes, antioxidants, polyamines, maintenance of hormone homeostasis, modification of transporters and/or regulatory proteins, including transcription factors and alternative splicing events. Occasionally, genetic manipulation of regulatory proteins or phytohormone levels confers salinity tolerance, but all these may cause undesired reduction in plant growth and/or yields. In this review, we present and evaluate novel and cutting-edge approaches for engineering salt tolerance in crop plants. First, we cover recent findings regarding the importance of regulatory proteins and transporters, and how they can be used to enhance salt tolerance in crop plants. We also evaluate the importance of halobiomes as a reservoir of genes that can be used for engineering salt tolerance in glycophytic crops. Additionally, the role of microRNAs as critical post-transcriptional regulators in plant adaptive responses to salt stress is reviewed and their use for engineering salt-tolerant crop plants is critically assessed. The potentials of alternative splicing mechanisms and targeted gene-editing technologies in understanding plant salt stress responses and developing salt-tolerant crop plants are also discussed.
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2.
CRISPR-associated nucleases: the Dawn of a new age of efficient crop improvement.
Ghogare, R, Williamson-Benavides, B, Ramírez-Torres, F, Dhingra, A
Transgenic research. 2020;(1):1-35
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Abstract
The world stands at a new threshold today. As a planet, we face various challenges, and the key one is how to continue to produce enough food, feed, fiber, and fuel to support the burgeoning population. In the past, plant breeding and the ability to genetically engineer crops contributed to increasing food production. However, both approaches rely on random mixing or integration of genes, and the process can be unpredictable and time-consuming. Given the challenge of limited availability of natural resources and changing environmental conditions, the need to rapidly and precisely improve crops has become urgent. The discovery of CRISPR-associated endonucleases offers a precise yet versatile platform for rapid crop improvement. This review summarizes a brief history of the discovery of CRISPR-associated nucleases and their application in genome editing of various plant species. Also provided is an overview of several new endonucleases reported recently, which can be utilized for editing of specific genes in plants through various forms of DNA sequence alteration. Genome editing, with its ever-expanding toolset, increased efficiency, and its potential integration with the emerging synthetic biology approaches hold promise for efficient crop improvement to meet the challenge of supporting the needs of future generations.
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3.
Improving RNAi efficiency for pest control in crop species.
Yan, S, Ren, B, Zeng, B, Shen, J
BioTechniques. 2020;(5):283-290
Abstract
The application of RNAi promotes the development of novel approaches toward plant protection in a sustainable way. Genetically modified crops expressing dsRNA have been developed as commercial products with great potential in insect pest management. Alternatively, some nontransformative approaches, including foliar spray, irrigation and trunk injection, are favorable in actual utilization. In this review, we summarize the recent progress and successful cases of RNAi-based pest management strategy, explore essential implications and possibilities to improve RNAi efficiency by delivery of dsRNA through transformative and nontransformative approaches, and highlight the remaining challenges and important issues related to the application of this technology.
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4.
Exploitation of genetic resources based on regulome and gene editing in crops.
Li, Y, Yan, W
Science China. Life sciences. 2020;(9):1406-1409
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5.
A critical look on CRISPR-based genome editing in plants.
Ahmad, N, Rahman, MU, Mukhtar, Z, Zafar, Y, Zhang, B
Journal of cellular physiology. 2020;(2):666-682
Abstract
Clustered regularly interspaced short palindromic repeats (CRISPR)-based genome editing, derived from prokaryotic immunity system, is rapidly emerging as an alternative platform for introducing targeted alterations in genomes. The CRISPR-based tools have been deployed for several other applications including gene expression studies, detection of mutation patterns in genomes, epigenetic regulation, chromatin imaging, etc. Unlike the traditional genetic engineering approaches, it is simple, cost-effective, and highly specific in inducing genetic variations. Despite its popularity, the technology has limitations such as off-targets, low mutagenesis efficiency, and its dependency on in-vitro regeneration protocols for the recovery of stable plant lines. Several other issues such as persisted CRISPR activity in subsequent generations, the potential for transferring to its wild type population, the risk of reversion of edited version to its original phenotype particularly in cross-pollinated plant species when released into the environment and the scarcity of validated targets have been overlooked. This article briefly highlights these undermined aspects, which may challenge the wider applications of this platform for improving crop genetics.
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6.
Applying gene editing to tailor precise genetic modifications in plants.
Van Eck, J
The Journal of biological chemistry. 2020;(38):13267-13276
Abstract
The ability to tailor alterations in genomes, including plant genomes, in a site-specific manner has been greatly advanced through approaches that reduced the complexity and time of genome sequencing along with development of gene editing technologies. These technologies provide a valuable foundation for studies of gene function, metabolic engineering, and trait modification for crop improvement. Development of genome editing methodologies began ∼20 years ago, first with meganucleases and followed by zinc finger nucleases, transcriptional activator-like effector nucleases and, most recently, clustered regulatory interspaced short palindromic repeat (CRISPR)-associated protein (Cas) (CRISPR/Cas), which is by far the most utilized method. The premise of CRISPR/Cas centers on the cleaving of one or both DNA strands by a Cas protein, an endonuclease, followed by mending of the DNA by repair mechanisms inherent in cells. Its user-friendly construct design, greater flexibility in targeting genomic regions, and cost-effective attributes have resulted in it being widely adopted and revolutionizing precise modification of the genomes of many organisms. Indeed, the CRISPR/Cas system has been utilized for gene editing in many plant species, including important food crops, such as maize, wheat, rice, and potatoes. This review summarizes the various approaches, including the most recent designs being used to make modifications from as small as a single-base-pair change to insertion of DNA fragments. On the gene expression level, strategies are presented that make it possible to knock out or modulate through activation and repression. Also discussed are prerequisites necessary for CRISPR/Cas-mediated editing as well as the current challenges.
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Report on the SCRA Nuts and Bolts Workshop II: case studies of citrus greening, Ultra-low Gossypol Cotton, and blight tolerant, low-acrylamide potato.
Hood, EE, Eversole, KA, Leach, L, Hogan, M, McHughen, A, Cordts, J, Rathore, K, Rood, T, Collinge, S, Irey, M
GM crops & food. 2019;(3):139-158
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Abstract
To be commercialized and grown in the US, genetically engineered (GE) crops typically go through an extensive food, feed, and environmental safety assessment process which, in certain instances, requires complex consultations with three different US regulatory agencies. Many small market, niche, and specialty crops have been genetically engineered using the modern tools of recombinant DNA but few have been commercialized due to real or perceived regulatory constraints. This workshop discussed the practical aspects of developing dossiers on GE specialty, niche, or small-market crops/products for submission to US regulatory agencies. This workshop focused on actual case studies, and provided an opportunity for public or private sector scientists and crop developers to spend time with regulatory officials to learn the specifics of compiling a dossier for regulatory approval. The objective of the workshop was to explain and demystify data requirements and regulatory dossier compilation by small companies, academics, and other developers.
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From bacterial battles to CRISPR crops; progress towards agricultural applications of genome editing.
Bryant, JA
Emerging topics in life sciences. 2019;(6):687-693
Abstract
Genome editing is the precise alteration of DNA in living cells by the cutting or removal of specific sequences, sometimes followed by insertion of new sequences at the cut site. CRISPR-Cas9 has become firmly established as the genome-editing method of choice, replacing the systems that had been developed and in use since the early 1990s. The CRISPR-Cas9 system has been developed from a mechanism used in prokaryotes as a defence against bacteriophage but actually functions in cells of all types of organisms. It is widely used in research as a gene knockout and editing tool; applications in veterinary medicine (such as increased resistance to disease) and human medicine (such as correction of disease-causing mutations) are under development. In agriculture and horticulture, the potential for various aspects of crop improvement is very large. Selected aspects of this potential are presented here, with particular focus on crop quality and disease resistance. The article ends with a brief discussion of the regulatory 'environment' in the USA and the EU.
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Hybrid wheat: past, present and future.
Gupta, PK, Balyan, HS, Gahlaut, V, Saripalli, G, Pal, B, Basnet, BR, Joshi, AK
TAG. Theoretical and applied genetics. Theoretische und angewandte Genetik. 2019;(9):2463-2483
Abstract
The review outlines past failures, present status and future prospects of hybrid wheat, and includes information on CMS/CHA/transgenic approaches for male sterility, heterotic groups and cost-effective hybrid seed production. Hybrid varieties give increased yield and improved grain quality in both cross- and self-pollinated crops. However, hybrid varieties in self-pollinated crops (particularly cereals) have not been very successful, except for hybrid rice in China. In case of hybrid wheat, despite the earlier failures, renewed efforts in recent years have been made and hybrid varieties with desirable attributes have been produced and marketed in some European countries. This review builds upon previous reviews, with a new outlook and improved knowledge base, not covered in earlier reviews. New technologies have been described, which include the Hordeum chilense-based CMS-fertility restorer system, chromosomal XYZ-4E-ms system and the following transgenic technologies: (1) conditional male sterility involving use of tapetum-specific expression of a gene that converts a pro-toxin into a phytotoxin causing male sterility; (2) barnase-barstar SeedLink system of Bayer CropScience; (3) split-barnase system that obviates the need of a barstar-based male restorer line; and (4) seed production technology of DuPont-Pioneer that makes use of transgenes in production of male-sterile lines, but gives hybrid seed with no transgenes. This review also includes a brief account of studies for discovery of heterotic QTL, genomic prediction of hybrid vigour and the development of heterotic groups/patterns and their importance in hybrid wheat production. The problem of high cost of hybrid seed due to required high seed rate in wheat relative to hybrid rice has also been addressed. The review concludes with a brief account of the current efforts and future possibilities in making hybrid wheat a commercial success.
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Developing Transgenic Agronomic Traits for Crops: Targets, Methods, and Challenges.
Davies, JP, Christensen, CA
Methods in molecular biology (Clifton, N.J.). 2019;:343-365
Abstract
The last two decades have witnessed a surge of investment by the agricultural biotechnology industry in the development of transgenic agronomic traits. These are traits that improve yield performance by modifying endogenous physiological processes such as energy capture, nutrient utilization, and stress tolerance. In this chapter we provide a foundation for understanding these fundamental processes and then outline approaches that have been taken to use this knowledge for yield improvement. We characterize the current status of product development pipelines in the industry and illustrate the trait discovery process with three important examples-bacterial cold-shock proteins, alanine aminotransferase, and auxin-regulated genes. The challenges with developing and commercializing an agronomic trait product are discussed.