Precise CRISPR-Cas9 Mediated Genome Editing in Super Basmati Rice for Resistance Against Bacterial Blight by Targeting the Major Susceptibility Gene

Rice Promoter Editing: An Efficient Genetic Improvement Strategy

Gene expression levels in rice (Oryza sativa L.) and other plant species are determined by the promoters, which directly control phenotypic characteristics. As essential components of genes, promoters regulate the intensity, location, and timing of gene expression. They contain numerous regulatory elements and serve as binding sites for proteins that modulate transcription, including transcription factors and RNA polymerases. Genome editing can alter promoter sequences, thereby precisely modifying the expression patterns of specific genes, and ultimately affecting the morphology, quality, and resistance of rice. This paper summarizes research on rice promoter editing conducted in recent years, focusing on improvements in yield, heading date, quality, and disease resistance. It is expected to inform the application of promoter editing and encourage further research and development in crop genetic improvement with promote.

The potential of genome editing to create novel alleles of resistance genes in rice

Rice, a staple food for a significant portion of the global population, faces persistent threats from various pathogens and pests, necessitating the development of resilient crop varieties. Deployment of resistance genes in rice is the best practice to manage diseases and reduce environmental damage by reducing the application of agro-chemicals. Genome editing technologies, such as CRISPR-Cas, have revolutionized the field of molecular biology, offering precise and efficient tools for targeted modifications within the rice genome. This study delves into the application of these tools to engineer novel alleles of resistance genes in rice, aiming to enhance the plant's innate ability to combat evolving threats. By harnessing the power of genome editing, researchers can introduce tailored genetic modifications that bolster the plant's defense mechanisms without compromising its essential characteristics. In this study, we synthesize recent advancements in genome editing methodologies applicable to rice and discuss the ethical considerations and regulatory frameworks surrounding the creation of genetically modified crops. Additionally, it explores potential challenges and future prospects for deploying edited rice varieties in agricultural landscapes. In summary, this study highlights the promise of genome editing in reshaping the genetic landscape of rice to confront emerging challenges, contributing to global food security and sustainable agriculture practices.

Towards DNA-free CRISPR/Cas9 genome editing for sustainable oil palm improvement

The CRISPR/Cas9 genome editing system has been in the spotlight compared to programmable nucleases such as ZFNs and TALENs due to its simplicity, versatility, and high efficiency. CRISPR/Cas9 has revolutionized plant genetic engineering and is broadly used to edit various plants' genomes, including those transformation-recalcitrant species such as oil palm. This review will comprehensively present the CRISPR-Cas9 system's brief history and underlying mechanisms. We then highlighted the establishment of the CRISPR/Cas9 system in plants with an emphasis on the strategies of highly efficient guide RNA design, the establishment of various CRISPR/Cas9 vector systems, approaches of multiplex editing, methods of transformation for stable and transient techniques, available methods for detecting and analyzing mutations, which have been applied and could be adopted for CRISPR/Cas9 genome editing in oil palm. In addition, we also provide insight into the strategy of DNA-free genome editing and its potential application in oil palm.

Application of genome editing techniques to regulate gene expression in crops

BACKGROUND

Enhanced agricultural production is urgently required to meet the food demands of the increasing global population. Abundant genetic diversity is expected to accelerate crop development. In particular, the development of the CRISPR/Cas genome editing technology has greatly enhanced our ability to improve crop's genetic diversity through direct artificial gene modification. However, recent studies have shown that most crop improvement efforts using CRISPR/Cas techniques have mainly focused on the coding regions, and there is a relatively lack of studies on the regulatory regions of gene expression.

RESULTS

This review briefly summarizes the development of CRISPR/Cas system in the beginning. Subsequently, the importance of gene regulatory regions in plants is discussed. The review focuses on recent developments and applications of mutations in regulatory regions via CRISPR/Cas techniques in crop breeding.

CONCLUSION

Finally, an outline of perspectives for future crop breeding using genome editing technologies is provided. This review provides new research insights for crop improvement using genome editing techniques.

Generating Mutant for a Stress-Responsive Gene in Rice Using CRISPR-Cas9 System

CRISPR/Cas9 system is one of the most often utilized engineering tools for genome editing in many organisms including crop plants and presents great value in both basic and applied research. This is a preferred method because of its relative simplicity, cost-effectiveness, and reliability. The Cas9 nuclease guided by a short single guide RNA (gRNA) can generate double-strand DNA breaks (DSB) at the specific sites in chromosomal DNA. The DSB site is repaired by error-prone repair methods. During repair, some nucleotides are deleted or added at the target site. Here, we present a simplified protocol for generating mutants in gene of interest in rice using CRISPR/Cas9.

CRISPR/Cas9-mediated genome editing techniques and new breeding strategies in cereals - current status, improvements, and perspectives

Cereal crops, including triticeae species (barley, wheat, rye), as well as edible cereals (wheat, corn, rice, oat, rye, sorghum), are significant suppliers for human consumption, livestock feed, and breweries. Over the past half-century, modern varieties of cereal crops with increased yields have contributed to global food security. However, presently cultivated elite crop varieties were developed mainly for optimal environmental conditions. Thus, it has become evident that taking into account the ongoing climate changes, currently a priority should be given to developing new stress-tolerant cereal cultivars. It is necessary to enhance the accuracy of methods and time required to generate new cereal cultivars with the desired features to adapt to climate change and keep up with the world population expansion. The CRISPR/Cas9 system has been developed as a powerful and versatile genome editing tool to achieve desirable traits, such as developing high-yielding, stress-tolerant, and disease-resistant transgene-free lines in major cereals. Despite recent advances, the CRISPR/Cas9 application in cereals faces several challenges, including a significant amount of time required to develop transgene-free lines, laboriousness, and a limited number of genotypes that may be used for the transformation and in vitro regeneration. Additionally, developing elite lines through genome editing has been restricted in many countries, especially Europe and New Zealand, due to a lack of flexibility in GMO regulations. This review provides a comprehensive update to researchers interested in improving cereals using gene-editing technologies, such as CRISPR/Cas9. We will review some critical and recent studies on crop improvements and their contributing factors to superior cereals through gene-editing technologies.

Nanotechnology and CRISPR/Cas9 system for sustainable agriculture

The clustered regularly interspaced short palindromic repeats (CRISPR-Cas9), a genome editing tool, has gained a tremendous position due to its therapeutic efficacy, ability to counteract abiotic/biotic stresses in plants, environmental remediation and sustainable agriculture with the aim of food security. This is mainly due to their potential of precised genome modification and numerous genetic engineering protocols with versatility as well as simplicity. This technique is quite useful for crop refinement and overcoming the agricultural losses and regaining the soil fertility hampered by hazardous chemicals. Since CRISPR/Cas9 has been widely accepted in genome editing in plants, however, their revolutionised nature and progress enable genetic engineers to face numerous challenges in plant biotechnology. Therefore, nanoparticles have addressed these challenges and improved cargo delivery and genomic editing processes. Henceforth, this barrier prevents CRISPR-based genetic engineering in plants in order to show efficacy in full potential and eliminate all the barriers. This advancement accelerates the genome editing process and its applications in plant biotechnology enable us to sustain and feed the massive population under varying environments. Genome editing tools using CRISPR/Cas9 and nanotechnology are advantageous that produce transgenic-free plants that overcome global food demands. Here, in this review, we have aimed towards the mechanisms/delivery systems linked with CRISPR/Cas9 system. We have elaborated on the applications of CRISPR/Cas9 and nanotechnology-based systems for sustainable agriculture. Moreover, the challenges and limitations associated with genome editing and delivery systems have also been discussed with a special emphasis on crop improvement.

Genome editing for healthy crops: traits, tools and impacts

Crop cultivars in commercial use have often been selected because they show high levels of resistance to pathogens. However, widespread cultivation of these crops for many years in the environments favorable to a pathogen requires durable forms of resistance to maintain "healthy crops". Breeding of new varieties tolerant/resistant to biotic stresses by incorporating genetic components related to durable resistance, developing new breeding methods and new active molecules, and improving the Integrated Pest Management strategies have been of great value, but their effectiveness is being challenged by the newly emerging diseases and the rapid change of pathogens due to climatic changes. Genome editing has provided new tools and methods to characterize defense-related genes in crops and improve crop resilience to disease pathogens providing improved food security and future sustainable agricultural systems. In this review, we discuss the principal traits, tools and impacts of utilizing genome editing techniques for achieving of durable resilience and a "healthy plants" concept.

CRISPR-Cas System, a Possible "Savior" of Rice Threatened by Climate Change: An Updated Review

Climate change has significantly affected agriculture production, particularly the rice crop that is consumed by almost half of the world's population and contributes significantly to global food security. Rice is vulnerable to several abiotic and biotic stresses such as drought, heat, salinity, heavy metals, rice blast, and bacterial blight that cause huge yield losses in rice, thus threatening food security worldwide. In this regard, several plant breeding and biotechnological techniques have been used to raise such rice varieties that could tackle climate changes. Nowadays, gene editing (GE) technology has revolutionized crop improvement. Among GE technology, CRISPR/Cas (Clustered Regularly Interspaced Short Palindromic Repeats/CRISPR-associated protein) system has emerged as one of the most convenient, robust, cost-effective, and less labor-intensive system due to which it has got more popularity among plant researchers, especially rice breeders and geneticists. Since 2013 (the year of first application of CRISPR/Cas-based GE system in rice), several trait-specific climate-resilient rice lines have been developed using CRISPR/Cas-based GE tools. Earlier, several reports have been published confirming the successful application of GE tools for rice improvement. However, this review particularly aims to provide an updated and well-synthesized brief discussion based on the recent studies (from 2020 to present) on the applications of GE tools, particularly CRISPR-based systems for developing CRISPR rice to tackle the current alarming situation of climate change, worldwide. Moreover, potential limitations and technical bottlenecks in the development of CRISPR rice, and prospects are also discussed.

Biotechnologically Engineered Plants

The development of recombinant DNA technology during the past thirty years has enabled scientists to isolate, characterize, and manipulate a myriad of different animal, bacterial, and plant genes. This has, in turn, led to the commercialization of hundreds of useful products that have significantly improved human health and well-being. Commercially, these products have been mostly produced in bacterial, fungal, or animal cells grown in culture. More recently, scientists have begun to develop a wide range of transgenic plants that produce numerous useful compounds. The perceived advantage of producing foreign compounds in plants is that compared to other methods of producing these compounds, plants seemingly provide a much less expensive means of production. A few plant-produced compounds are already commercially available; however, many more are in the production pipeline.

Multi-faceted CRISPR-Cas9 strategy to reduce plant based food loss and waste for sustainable bio-economy - A review

Currently, international development requires innovative solutions to address imminent challenges like climate change, unsustainable food system, food waste, energy crisis, and environmental degradation. All the same, addressing these concerns with conventional technologies is time-consuming, causes harmful environmental impacts, and is not cost-effective. Thus, biotechnological tools become imperative for enhancing food and energy resilience through eco-friendly bio-based products by valorisation of plant and food waste to meet the goals of circular bioeconomy in conjunction with Sustainable Developmental Goals (SDGs). Genome editing can be accomplished using a revolutionary DNA modification tool, CRISPR-Cas9, through its uncomplicated guided mechanism, with great efficiency in various organisms targeting different traits. This review's main objective is to examine how the CRISPR-Cas system, which has positive features, could improve the bioeconomy by reducing food loss and waste with all-inclusive food supply chain both at on-farm and off-farm level; utilising food loss and waste by genome edited microorganisms through food valorisation; efficient microbial conversion of low-cost substrates as biofuel; valorisation of agro-industrial wastes; mitigating greenhouse gas emissions through forestry plantation crops; and protecting the ecosystem and environment. Finally, the ethical implications and regulatory issues that are related to CRISPR-Cas edited products in the international markets have also been taken into consideration.

Enhancing the quality of staple food crops through CRISPR/Cas-mediated site-directed mutagenesis

The enhancement of CRISPR-Cas gene editing with robust nuclease activity promotes genetic modification of desirable agronomic traits, such as resistance to pathogens, drought tolerance, nutritional value, and yield-related traits in crops. The genetic diversity of food crops has reduced tremendously over the past twelve millennia due to plant domestication. This reduction presents significant challenges for the future especially considering the risks posed by global climate change to food production. While crops with improved phenotypes have been generated through crossbreeding, mutation breeding, and transgenic breeding over the years, improving phenotypic traits through precise genetic diversification has been challenging. The challenges are broadly associated with the randomness of genetic recombination and conventional mutagenesis. This review highlights how emerging gene-editing technologies reduce the burden and time necessary for developing desired traits in plants. Our focus is to provide readers with an overview of the advances in CRISPR-Cas-based genome editing for crop improvement. The use of CRISPR-Cas systems in generating genetic diversity to enhance the quality and nutritional value of staple food crops is discussed. We also outlined recent applications of CRISPR-Cas in developing pest-resistant crops and removing unwanted traits, such as allergenicity from crops. Genome editing tools continue to evolve and present unprecedented opportunities to enhance crop germplasm via precise mutations at the desired loci of the plant genome.

Employing template-directed CRISPR-based editing of the OsALS gene to create herbicide tolerance in Basmati rice

Rice (Oryza sativa) is one of the primary food crops which contributes major portion of daily calorie intake. It is used as model crop for various genome editing studies. Basmati rice was also explored for establishing non-homologous end joining-based genome editing. But it was not clear whether homology-directed repair (HDR)-based genome editing can be done in Basmati rice. The current study was designed to establish HDR-based genome editing in Basmati rice to develop herbicide tolerance. There is severe weed spread when rice is grown via direct planted rice method in various countries to save labour and water resources. Therefore, the use of herbicides is necessary to control weeds. These herbicides can also affect cultivated rice which creates the need to develop herbicide-tolerant rice. In current study, we introduced a point mutation in Acetolactate Synthase gene to convert tryptophan to leucine at position 548. For this purpose, different constructs for HDR were tested with different RNA scaffold and orientation of repair templates. Out of four different architectures, the one having repair template identical to the target DNA strand precisely edited the target site. We successfully established template-directed CRISPR-Cas9 system in Super Basmati rice by detecting desired substitutions at the target site in Acetolactate Synthase locus. Moreover, this editing of Acetolactate Synthase gene resulted in the production of herbicide tolerance in Super Basmati rice. This study suggests that such type of HDR system can be used to precisely edit other genes for crop improvement.

Genetically engineered crops for sustainably enhanced food production systems

Genetic modification of crops has substantially focused on improving traits for desirable outcomes. It has resulted in the development of crops with enhanced yields, quality, and tolerance to biotic and abiotic stresses. With the advent of introducing favorable traits into crops, biotechnology has created a path for the involvement of genetically modified (GM) crops into sustainable food production systems. Although these plants heralded a new era of crop production, their widespread adoption faces diverse challenges due to concerns about the environment, human health, and moral issues. Mitigating these concerns with scientific investigations is vital. Hence, the purpose of the present review is to discuss the deployment of GM crops and their effects on sustainable food production systems. It provides a comprehensive overview of the cultivation of GM crops and the issues preventing their widespread adoption, with appropriate strategies to overcome them. This review also presents recent tools for genome editing, with a special focus on the CRISPR/Cas9 platform. An outline of the role of crops developed through CRSIPR/Cas9 in achieving sustainable development goals (SDGs) by 2030 is discussed in detail. Some perspectives on the approval of GM crops are also laid out for the new age of sustainability. The advancement in molecular tools through plant genome editing addresses many of the GM crop issues and facilitates their development without incorporating transgenic modifications. It will allow for a higher acceptance rate of GM crops in sustainable agriculture with rapid approval for commercialization. The current genetic modification of crops forecasts to increase productivity and prosperity in sustainable agricultural practices. The right use of GM crops has the potential to offer more benefit than harm, with its ability to alleviate food crises around the world.

A detailed landscape of CRISPR-Cas-mediated plant disease and pest management

Genome editing technology has rapidly evolved to knock-out genes, create targeted genetic variation, install precise insertion/deletion and single nucleotide changes, and perform large-scale alteration. The flexible and multipurpose editing technologies have started playing a substantial role in the field of plant disease management. CRISPR-Cas has reduced many limitations of earlier technologies and emerged as a versatile toolbox for genome manipulation. This review summarizes the phenomenal progress of the use of the CRISPR toolkit in the field of plant pathology. CRISPR-Cas toolbox aids in the basic studies on host-pathogen interaction, in identifying virulence genes in pathogens, deciphering resistance and susceptibility factors in host plants, and engineering host genome for developing resistance. We extensively reviewed the successful genome editing applications for host plant resistance against a wide range of biotic factors, including viruses, fungi, oomycetes, bacteria, nematodes, insect pests, and parasitic plants. Recent use of CRISPR-Cas gene drive to suppress the population of pathogens and pests has also been discussed. Furthermore, we highlight exciting new uses of the CRISPR-Cas system as diagnostic tools, which rapidly detect pathogenic microorganism. This comprehensive yet concise review discusses innumerable strategies to reduce the burden of crop protection.

CRISPR/Cas tool designs for multiplex genome editing and its applications in developing biotic and abiotic stress-resistant crop plants

Crop plants are prone to several yield-reducing biotic and abiotic stresses. The crop yield reductions due to these stresses need addressing to maintain an adequate balance between the increasing world population and food production to avoid food scarcities in the future. It is impossible to increase the area under food crops proportionately to meet the rising food demand. In such an adverse scenario overcoming the biotic and abiotic stresses through biotechnological interventions may serve as a boon to help meet the globe's food requirements. Under the current genomic era, the wide availability of genomic resources and genome editing technologies such as Transcription Activator-Like Effector Nucleases (TALENs), Zinc Finger Nucleases (ZFNs), and Clustered-Regularly Interspaced Palindromic Repeats/CRISPR-associated proteins (CRISPR/Cas) has widened the scope of overcoming these stresses for several food crops. These techniques have made gene editing more manageable and accessible with changes at the embryo level by adding or deleting DNA sequences of the target gene(s) from the genome. The CRISPR construct consists of a single guide RNA having complementarity with the nucleotide fragments of the target gene sequence, accompanied by a protospacer adjacent motif. The target sequence in the organism's genome is then cleaved by the Cas9 endonuclease for obtaining a desired trait of interest. The current review describes the components, mechanisms, and types of CRISPR/Cas techniques and how this technology has helped to functionally characterize genes associated with various biotic and abiotic stresses in a target organism. This review also summarizes the application of CRISPR/Cas technology targeting these stresses in crops through knocking down/out of associated genes.

Bioinformatics approaches and applications in plant biotechnology

BACKGROUND

In recent years, major advance in molecular biology and genomic technologies have led to an exponential growth in biological information. As the deluge of genomic information, there is a parallel growth in the demands of tools in the storage and management of data, and the development of software for analysis, visualization, modelling, and prediction of large data set.

MAIN BODY

Particularly in plant biotechnology, the amount of information has multiplied exponentially with a large number of databases available from many individual plant species. Efficient bioinformatics tools and methodologies are also developed to allow rapid genome sequence and the study of plant genome in the 'omics' approach. This review focuses on the various bioinformatic applications in plant biotechnology, and their advantages in improving the outcome in agriculture. The challenges or limitations faced in plant biotechnology in the aspect of bioinformatics approach that explained the low progression in plant genomics than in animal genomics are also reviewed and assessed.

CONCLUSION

There is a critical need for effective bioinformatic tools, which are able to provide longer reads with unbiased coverage in order to overcome the complexity of the plant's genome. The advancement in bioinformatics is not only beneficial to the field of plant biotechnology and agriculture sectors, but will also contribute enormously to the future of humanity.

CRISPR/Cas9-Mediated Targeting of Susceptibility Factor eIF4E-Enhanced Resistance Against Potato Virus Y

Potato (Solanum tuberosum L.) is an important staple food around the world, and potato virus Y (PVY) is a major constraint for potato production. The VPg protein of PVY interacts with the translation initiation factor eIF4E of the host that works as a susceptibility factor during infection. The interaction between eIF4E and VPg was disrupted by CRISPR/Cas9. The homozygous conserved region of eIF4E of the potato variety “Kruda” was mutated by CRISPR/Cas9. Tracking of insertion, deletion, and conversion events was performed by Sanger sequencing with ∼15% editing efficiency. Truncated and mutated eIF4E proteins were unable to interact with VPg, and the virus was not able to exploit the host machinery for replication and systemic spreading. Mutated eIF4E lines showed enhanced resistance to PVYO strain. DAS-ELISA and RT-PCR were used for validation of the observed resistance. PVY resistance in tetraploid lines via CRISPR/Cas9 provides a route to develop novel resistant potato cultivars.

Genome edited wheat- current advances for the second green revolution

Common wheat is a major source of nutrition around the globe, but unlike maize and rice hybrids, no breakthrough has been made to enhance wheat yield since Green Revolution. With the availability of reference genome sequence of wheat and advancement of allied genomics technologies, understanding of genes involved in grain yield components and disease resistance/susceptibility has opened new avenues for crop improvement. Wheat has a huge hexaploidy genome of approximately 17 GB with 85% repetition, and it is a daunting task to induce any mutation across three homeologues that can be helpful for the enhancement of agronomic traits. The CRISPR-Cas9 system provides a promising platform for genome editing in a site-specific manner. In wheat, CRISPR-Cas9 is being used in the improvement of yield, grain quality, biofortification, resistance against diseases, and tolerance against abiotic factors. The promising outcomes of the CRISPR-based multiplexing approach circumvent the constraint of targeting merely one gene at a time. Deployment of clustered regularly interspaced short palindromic repeats (CRISPR)-associated (Cas) 9 endonuclease (CRISPR-Cas9) and Cas9 variant systems such as cytidine base editing, adenosine base editing, and prime editing in wheat has been used to induce point mutations more precisely. Scientists have acquired major events such as induction of male sterility, fertility restoration, and alteration of seed dormancy through Cas9 in wheat that can facilitate breeding programs for elite variety development. Furthermore, a recent discovery in tissue culturing enables scientists to significantly enhance regeneration efficiency in wheat by transforming the GRF4-GIF1 cassette. Rapid generation advancement by speed breeding technology provides the opportunity for the generation advancement of the desired plants to segregate out unwanted transgenes and allows rapid integration of gene-edited wheat into the breeding pipeline. The combination of these novel technologies addresses some of the most important limiting factors for sustainable and climate-smart wheat that should lead to the second "Green Revolution" for global food security.

Reverse genetic approaches for breeding nutrient-rich and climate-resilient cereal and food legume crops

In the last decade, advancements in genomics tools and techniques have led to the discovery of many genes. Most of these genes still need to be characterized for their associated function and therefore, such genes remain underutilized for breeding the next generation of improved crop varieties. The recent developments in different reverse genetic approaches have made it possible to identify the function of genes controlling nutritional, biochemical, and metabolic traits imparting drought, heat, cold, salinity tolerance as well as diseases and insect-pests. This article focuses on reviewing the current status and prospects of using reverse genetic approaches to breed nutrient-rich and climate resilient cereal and food legume crops.

A review of approaches to control bacterial leaf blight in rice

The Gram-negative bacteria Xanthomonas oryzae pv. oryzae, the causative agent of bacterial leaf blight (BLB), received attention for being an economically damaging pathogen of rice worldwide. This damage prompted efforts to better understand the molecular mechanisms governing BLB disease progression. This research revealed numerous virulence factors that are employed by this vascular pathogen to invade the host, outcompete host defence mechanisms, and cause disease. In this review, we emphasize the virulence factors and molecular mechanisms that X. oryzae pv. oryzae uses to impair host defences, recent insights into the cellular and molecular mechanisms underlying host-pathogen interactions and components of pathogenicity, methods for developing X. oryzae pv. oryzae-resistant rice cultivars, strategies to mitigate disease outbreaks, and newly discovered genes and tools for disease management. We conclude that the implementation and application of cutting-edge technologies and tools are crucial to avoid yield losses from BLB and ensure food security.

The Rice ILI2 Locus Is a Bidirectional Target of the African Xanthomonas oryzae pv. oryzae Major Transcription Activator-like Effector TalC but Does Not Contribute to Disease Susceptibility

Xanthomonas oryzae pv. oryzae (Xoo) strains that cause bacterial leaf blight (BLB) limit rice (Oryza sativa) production and require breeding more resistant varieties. Transcription activator-like effectors (TALEs) activate transcription to promote leaf colonization by binding to specific plant host DNA sequences termed effector binding elements (EBEs). Xoo major TALEs universally target susceptibility genes of the SWEET transporter family. TALE-unresponsive alleles of clade III OsSWEET susceptibility gene promoter created with genome editing confer broad resistance on Asian Xoo strains. African Xoo strains rely primarily on the major TALE TalC, which targets OsSWEET14. Although the virulence of a talC mutant strain is severely impaired, abrogating OsSWEET14 induction with genome editing does not confer equivalent resistance on African Xoo. To address this contradiction, we postulated the existence of a TalC target susceptibility gene redundant with OsSWEET14. Bioinformatics analysis identified a rice locus named ATAC composed of the INCREASED LEAF INCLINATION 2 (ILI2) gene and a putative lncRNA that are shown to be bidirectionally upregulated in a TalC-dependent fashion. Gain-of-function approaches with designer TALEs inducing ATAC sequences did not complement the virulence of a Xoo strain defective for SWEET gene activation. While editing the TalC EBE at the ATAC loci compromised TalC-mediated induction, multiplex edited lines with mutations at the OsSWEET14 and ATAC loci remained essentially susceptible to African Xoo strains. Overall, this work indicates that ATAC is a probable TalC off-target locus but nonetheless documents the first example of divergent transcription activation by a native TALE during infection.

Genome Editing for Sustainable Agriculture in Africa

Sustainable intensification of agriculture in Africa is essential for accomplishing food and nutritional security and addressing the rising concerns of climate change. There is an urgent need to close the yield gap in staple crops and enhance food production to feed the growing population. In order to meet the increasing demand for food, more efficient approaches to produce food are needed. All the tools available in the toolbox, including modern biotechnology and traditional, need to be applied for crop improvement. The full potential of new breeding tools such as genome editing needs to be exploited in addition to conventional technologies. Clustered regularly interspaced short palindromic repeats/CRISPR-associated protein (CRISPR/Cas)-based genome editing has rapidly become the most prevalent genetic engineering approach for developing improved crop varieties because of its simplicity, efficiency, specificity, and easy to use. Genome editing improves crop variety by modifying its endogenous genome free of any foreign gene. Hence, genome-edited crops with no foreign gene integration are not regulated as genetically modified organisms (GMOs) in several countries. Researchers are using CRISPR/Cas-based genome editing for improving African staple crops for biotic and abiotic stress resistance and improved nutritional quality. Many products, such as disease-resistant banana, maize resistant to lethal necrosis, and sorghum resistant to the parasitic plant Striga and enhanced quality, are under development for African farmers. There is a need for creating an enabling environment in Africa with science-based regulatory guidelines for the release and adoption of the products developed using CRISPR/Cas9-mediated genome editing. Some progress has been made in this regard. Nigeria and Kenya have recently published the national biosafety guidelines for the regulation of gene editing. This article summarizes recent advances in developments of tools, potential applications of genome editing for improving staple crops, and regulatory policies in Africa.

TALEs as double-edged swords in plant-pathogen interactions: Progress, challenges, and perspectives

Xanthomonas species colonize many host plants and cause huge losses worldwide. Transcription activator-like effectors (TALEs) are secreted by Xanthomonas and translocated into host cells to manipulate the expression of target genes, especially by Xanthomonas oryzae pv. oryzae and Xanthomonas oryzae pv. oryzicola, which cause bacterial blight and bacterial leaf streak, respectively, in rice. In this review, we summarize the progress of studies on the interaction between Xanthomonas and hosts, covering both rice and other plants. TALEs are not only key factors that make plants susceptible but are also essential components of plant resistance. Characterization of TALEs and TALE-like proteins has improved our understanding of TALE evolution and promoted the development of gene editing tools. In addition, the interactions between TALEs and hosts have also provided strategies and possibilities for genetic engineering in crop improvement.

From Functional Characterization to the Application of SWEET Sugar Transporters in Plant Resistance Breeding

The occurrence of plant diseases severely affects the quality and quantity of plant production. Plants adapt to the constant invasion of pathogens and gradually form a series of defense mechanisms, such as pathogen-associated molecular pattern-triggered immunity and microbial effector-triggered immunity. Moreover, many pathogens have evolved to inhibit the immune defense system and acquire plant nutrients as a result of their coevolution with plants. The sugars will eventually be exported transporters (SWEETs) are a novel family of sugar transporters that function as uniporters. They provide a channel for pathogens, including bacteria, fungi, and viruses, to hijack sugar from the host. In this review, we summarize the functions of SWEETs in nectar secretion, grain loading, senescence, and long-distance transport. We also focus on the interaction between the SWEET genes and pathogens. In addition, we provide insight into the potential application of SWEET genes to enhance disease resistance through the use of genome editing tools. The summary and perspective of this review will deepen our understanding of the role of SWEETs during the process of pathogen infection and provide insights into resistance breeding.

Emerging Roles of SWEET Sugar Transporters in Plant Development and Abiotic Stress Responses

Sugars are the major source of energy in living organisms and play important roles in osmotic regulation, cell signaling and energy storage. SWEETs (Sugars Will Eventually be Exported Transporters) are the most recent family of sugar transporters that function as uniporters, facilitating the diffusion of sugar molecules across cell membranes. In plants, SWEETs play roles in multiple physiological processes including phloem loading, senescence, pollen nutrition, grain filling, nectar secretion, abiotic (drought, heat, cold, and salinity) and biotic stress regulation. In this review, we summarized the role of SWEET transporters in plant development and abiotic stress. The gene expression dynamics of various SWEET transporters under various abiotic stresses in different plant species are also discussed. Finally, we discuss the utilization of genome editing tools (TALENs and CRISPR/Cas9) to engineer SWEET genes that can facilitate trait improvement. Overall, recent advancements on SWEETs are highlighted, which could be used for crop trait improvement and abiotic stress tolerance.

CRISPR/Cas9 and Nanotechnology Pertinence in Agricultural Crop Refinement

The CRISPR/Cas9 (Clustered Regularly Interspaced Short Palindromic Repeats/CRISPR-associated protein 9) method is a versatile technique that can be applied in crop refinement. Currently, the main reasons for declining agricultural yield are global warming, low rainfall, biotic and abiotic stresses, in addition to soil fertility issues caused by the use of harmful chemicals as fertilizers/additives. The declining yields can lead to inadequate supply of nutritional food as per global demand. Grains and horticultural crops including fruits, vegetables, and ornamental plants are crucial in sustaining human life. Genomic editing using CRISPR/Cas9 and nanotechnology has numerous advantages in crop development. Improving crop production using transgenic-free CRISPR/Cas9 technology and produced fertilizers, pesticides, and boosters for plants by adopting nanotechnology-based protocols can essentially overcome the universal food scarcity. This review briefly gives an overview on the potential applications of CRISPR/Cas9 and nanotechnology-based methods in developing the cultivation of major agricultural crops. In addition, the limitations and major challenges of genome editing in grains, vegetables, and fruits have been discussed in detail by emphasizing its applications in crop refinement strategy.

OUP accepted manuscript

Transcription activator-like effectors (TALEs) are bacterial proteins with a programmable DNA-binding domain, which turned them into exceptional tools for biotechnology. TALEs contain a central array of consecutive 34 amino acid long repeats to bind DNA in a simple one-repeat-to-one-nucleotide manner. However, a few naturally occurring aberrant repeat variants break this strict binding mechanism, allowing for the recognition of an additional sequence with a −1 nucleotide frameshift. The limits and implications of this extended TALE binding mode are largely unexplored. Here, we analyse the complete diversity of natural and artificially engineered aberrant repeats for their impact on the DNA binding of TALEs. Surprisingly, TALEs with several aberrant repeats can loop out multiple repeats simultaneously without losing DNA-binding capacity. We also characterized members of the only natural TALE class harbouring two aberrant repeats and confirmed that their target is the major virulence factor OsSWEET13 from rice. In an aberrant TALE repeat, the position and nature of the amino acid sequence strongly influence its function. We explored the tolerance of TALE repeats towards alterations further and demonstrate that inserts as large as GFP can be tolerated without disrupting DNA binding. This illustrates the extraordinary DNA-binding capacity of TALEs and opens new uses in biotechnology.

New approaches to improve crop tolerance to biotic and abiotic stresses

During the last years, a great effort has been dedicated at the development and employment of diverse approaches for achieving more stress-tolerant and climate-flexible crops and sustainable yield increases to meet the food and energy demands of the future. The ongoing climate change is in fact leading to more frequent extreme events with a negative impact on food production, such as increased temperatures, drought, and soil salinization as well as invasive arthropod pests and diseases. In this review, diverse "green strategies" (e.g., chemical priming, root-associated microorganisms), and advanced technologies (e.g., genome editing, high-throughput phenotyping) are described on the basis of the most recent research evidence. Particularly, attention has been focused on the potential use in a context of sustainable and climate-smart agriculture (the so called "next agriculture generation") to improve plant tolerance and resilience to abiotic and biotic stresses. In addition, the gap between the results obtained in controlled experiments and those from application of these technologies in real field conditions (lab to field step) is also discussed.

Recent Progress in Rice Broad-Spectrum Disease Resistance

Rice is one of the most important food crops in the world. However, stable rice production is constrained by various diseases, in particular rice blast, sheath blight, bacterial blight, and virus diseases. Breeding and cultivation of resistant rice varieties is the most effective method to control the infection of pathogens. Exploitation and utilization of the genetic determinants of broad-spectrum resistance represent a desired way to improve the resistance of susceptible rice varieties. Recently, researchers have focused on the identification of rice broad-spectrum disease resistance genes, which include R genes, defense-regulator genes, and quantitative trait loci (QTL) against two or more pathogen species or many isolates of the same pathogen species. The cloning of broad-spectrum disease resistance genes and understanding their underlying mechanisms not only provide new genetic resources for breeding broad-spectrum rice varieties, but also promote the development of new disease resistance breeding strategies, such as editing susceptibility and executor R genes. In this review, the most recent advances in the identification of broad-spectrum disease resistance genes in rice and their application in crop improvement through biotechnology approaches during the past 10 years are summarized.

Improved bacterial leaf blight disease resistance in the major elite Vietnamese rice cultivar TBR225 via editing of the OsSWEET14 promoter

TBR225 is one of the most popular commercial rice varieties in Northern Vietnam. However, this variety is highly susceptible to bacterial leaf blight (BLB), a disease caused by Xanthomonas oryzae pv. oryzae (Xoo) which can lead to important yield losses. OsSWEET14 belongs to the SWEET gene family that encodes sugar transporters. Together with other Clade III members, it behaves as a susceptibility (S) gene whose induction by Asian Xoo Transcription-Activator-Like Effectors (TALEs) is absolutely necessary for disease. In this study, we sought to introduce BLB resistance in the TBR225 elite variety. First, two Vietnamese Xoo strains were shown to up-regulate OsSWEET14 upon TBR225 infection. To investigate if this induction is connected with disease susceptibility, nine TBR225 mutant lines with mutations in the AvrXa7, PthXo3 or TalF TALEs DNA target sequences of the OsSWEET14 promoter were obtained using the CRISPR/Cas9 editing system. Genotyping analysis of T0 and T1 individuals showed that mutations were stably inherited. None of the examined agronomic traits of three transgene-free T2 edited lines were significantly different from those of wild-type TBR225. Importantly, one of these T2 lines, harboring the largest homozygous 6-bp deletion, displayed decreased OsSWEET14 expression as well as a significantly reduced susceptibility to a Vietnamese Xoo strains and complete resistance to another one. Our findings indicate that CRISPR/Cas9 editing conferred an improved BLB resistance to a Vietnamese commercial elite rice variety.

Next-Generation Breeding Strategies for Climate-Ready Crops

Climate change is a threat to global food security due to the reduction of crop productivity around the globe. Food security is a matter of concern for stakeholders and policymakers as the global population is predicted to bypass 10 billion in the coming years. Crop improvement via modern breeding techniques along with efficient agronomic practices innovations in microbiome applications, and exploiting the natural variations in underutilized crops is an excellent way forward to fulfill future food requirements. In this review, we describe the next-generation breeding tools that can be used to increase crop production by developing climate-resilient superior genotypes to cope with the future challenges of global food security. Recent innovations in genomic-assisted breeding (GAB) strategies allow the construction of highly annotated crop pan-genomes to give a snapshot of the full landscape of genetic diversity (GD) and recapture the lost gene repertoire of a species. Pan-genomes provide new platforms to exploit these unique genes or genetic variation for optimizing breeding programs. The advent of next-generation clustered regularly interspaced short palindromic repeat/CRISPR-associated (CRISPR/Cas) systems, such as prime editing, base editing, and de nova domestication, has institutionalized the idea that genome editing is revamped for crop improvement. Also, the availability of versatile Cas orthologs, including Cas9, Cas12, Cas13, and Cas14, improved the editing efficiency. Now, the CRISPR/Cas systems have numerous applications in crop research and successfully edit the major crop to develop resistance against abiotic and biotic stress. By adopting high-throughput phenotyping approaches and big data analytics tools like artificial intelligence (AI) and machine learning (ML), agriculture is heading toward automation or digitalization. The integration of speed breeding with genomic and phenomic tools can allow rapid gene identifications and ultimately accelerate crop improvement programs. In addition, the integration of next-generation multidisciplinary breeding platforms can open exciting avenues to develop climate-ready crops toward global food security.

Genome editing for resistance against plant pests and pathogens

The conventional breeding of crops struggles to keep up with increasing food needs and ever-adapting pests and pathogens. Global climate changes have imposed another layer of complexity to biological systems, increasing the challenge to obtain improved crop cultivars. These dictate the development and application of novel technologies, like genome editing (GE), that assist targeted and fast breeding programs in crops, with enhanced resistance to pests and pathogens. GE does not require crossings, hence avoiding the introduction of undesirable traits through linkage in elite varieties, speeding up the whole breeding process. Additionally, GE technologies can improve plant protection by directly targeting plant susceptibility (S) genes or virulence factors of pests and pathogens, either through the direct edition of the pest genome or by adding the GE machinery to the plant genome or to microorganisms functioning as biocontrol agents (BCAs). Over the years, GE technology has been continuously evolving and more so with the development of CRISPR/Cas. Here we review the latest advancements of GE to improve plant protection, focusing on CRISPR/Cas-based genome edition of crops and pests and pathogens. We discuss how other technologies, such as host-induced gene silencing (HIGS) and the use of BCAs could benefit from CRISPR/Cas to accelerate the development of green strategies to promote a sustainable agriculture in the future.

Targeted editing of tomato carotenoid isomerase reveals the role of 5' UTR region in gene expression regulation

A deletion created by CRISPR/Cas9 system in the 5' UTR of the carotenoid isomerase gene in tomato leads to downregulation of the gene resulting in the low conversion of prolycopene to lycopene. CRISPR/Cas9 based genome editing is an effective and useful tool adopted from the bacterial immune response system for altering specific, pre-determined DNA sequences in eukaryotes. Such targeted changes are finding wide application in human health as well as in precision breeding of crop plants for improved traits. Mutations in the coding and regulatory regions can have varying impacts on the function of the gene. In the current study, we demonstrate this on tomato carotenoid isomerase, a key gene in the carotenoid biosynthesis pathway. Mutations were generated in the 5' UTR and exon 1 of the carotenoid isomerase gene using CRISPR/Cas9 expression via Agrobacterium-mediated transformation of tomato variety Periyakulam 1 (PKM1). Molecular and biochemical studies demonstrate that CRISPR-mediated point mutations in the exon sequence lead to complete knockout of protein function whereas deletion in 5' UTR region lowers the expression of the gene leading to changes in plant phenotype.

Deployment of Genetic and Genomic Tools Toward Gaining a Better Understanding of Rice-Xanthomonas oryzae pv. oryzae Interactions for Development of Durable Bacterial Blight Resistant Rice

Rice is the most important food crop worldwide and sustainable rice production is important for ensuring global food security. Biotic stresses limit rice production significantly and among them, bacterial blight (BB) disease caused by Xanthomonas oryzae pv. oryzae (Xoo) is very important. BB reduces rice yields severely in the highly productive irrigated and rainfed lowland ecosystems and in recent years; the disease is spreading fast to other rice growing ecosystems as well. Being a vascular pathogen, Xoo interferes with a range of physiological and biochemical exchange processes in rice. The response of rice to Xoo involves specific interactions between resistance (R) genes of rice and avirulence (Avr) genes of Xoo, covering most of the resistance genes except the recessive ones. The genetic basis of resistance to BB in rice has been studied intensively, and at least 44 genes conferring resistance to BB have been identified, and many resistant rice cultivars and hybrids have been developed and released worldwide. However, the existence and emergence of new virulent isolates of Xoo in the realm of a rapidly changing climate necessitates identification of novel broad-spectrum resistance genes and intensification of gene-deployment strategies. This review discusses about the origin and occurrence of BB in rice, interactions between Xoo and rice, the important roles of resistance genes in plant's defense response, the contribution of rice resistance genes toward development of disease resistance varieties, identification and characterization of novel, and broad-spectrum BB resistance genes from wild species of Oryza and also presents a perspective on potential strategies to achieve the goal of sustainable disease management.