CRISPR-Cas9 mediated genome editing of drought and salt tolerance (OsDST) gene in indica mega rice cultivar MTU1010

Cytokinin oxidase2-deficient mutants improve panicle and grain architecture through cytokinin accumulation and enhance drought tolerance in indica rice

KEY MESSAGE

The Osckx2 mutant accumulates cytokinin thereby enhancing panicle branching, grain yield, and drought tolerance, marked by improved survival rate, membrane integrity, and photosynthetic function. Cytokinins (CKs) are multifaceted hormones that regulate growth, development, and stress responses in plants. Cytokinins have been implicated in improved panicle architecture and grain yield; however, they are inactivated by the enzyme cytokinin oxidase (CKX). In this study, we developed a cytokinin oxidase 2 (Osckx2)-deficient mutant using CRISPR/Cas9 gene editing in indica rice and assessed its function under water-deficit and salinity conditions. Loss of OsCKX2 function increased grain number, secondary panicle branching, and overall grain yield through improved cytokinin content in the panicle tissue. Under drought conditions, the Osckx2 mutant conserved more water and demonstrated improved water-saving traits. Through reduced transpiration, Osckx2 mutants showed an improved survival response than the wild type to unset dehydration stress. Further, Osckx2 maintained chloroplast and membrane integrity and showed significantly improved photosynthetic function under drought conditions through enhanced antioxidant protection systems. The OsCKX2 function negatively affects panicle grain number and drought tolerance, with no discernible impact in response to salinity. The finding suggests the utility of the beneficial Osckx2 allele in breeding to develop climate-resilient, high-yielding cultivars for future food security.

CRISPR-Cas9 mediated understanding of plants' abiotic stress-responsive genes to combat changing climatic patterns

Multiple abiotic stresses like extreme temperatures, water shortage, flooding, salinity, and exposure to heavy metals are confronted by crop plants with changing climatic patterns. Prolonged exposure to these adverse environmental conditions leads to stunted plant growth and development with significant yield loss in crops. CRISPR-Cas9 genome editing tool is being frequently employed to understand abiotic stress-responsive genes. Noteworthy improvements in CRISPR-Cas technology have been made over the years, including upgradation of Cas proteins fidelity and efficiency, optimization of transformation protocols for different crop species, base and prime editing, multiplex gene-targeting, transgene-free editing, and graft-based heritable CRISPR-Cas9 approaches. These developments helped to improve the knowledge of abiotic stress tolerance in crops that could potentially be utilized to develop knock-out varieties and over-expressed lines to tackle the adverse effects of altered climatic patterns. This review summarizes the mechanistic understanding of heat, drought, salinity, and metal stress-responsive genes characterized so far using CRISPR-Cas9 and provides data on potential candidate genes that can be exploited by modern-day biotechnological tools to develop transgene-free genome-edited crops with better climate adaptability. Furthermore, the importance of early-maturing crop varieties to withstand abiotic stresses is also discussed in this review.

CRISPR/Cas9 opens new horizon of crop improvement under stress condition

Plants are exposed to a myriad of stresses, stemming from abiotic and biotic sources, significantly threatening agricultural productivity. The low crop yield, coupled with the global burden of population has resulted in the scarcity of quality food, exacerbating socio-economic issues like poverty, hunger, and malnutrition. Conventional breeding methods for the generation of stress-tolerant plants are time-consuming, limit genetic diversity, and are not sustainable for the consistent production of high-yielding crops. In recent years, the use of high-throughput, genome editing (GE) technique has revolutionized the crop-improvement paradigm, ushering greater prospects for agricultural progress. Among these tools, the Clustered regularly interspaced short palindromic repeat (CRISPR), and its associated nuclease protein Cas9, have appeared as a ground-breaking technology, allowing precise knockout (KO), upregulation, and downregulation of target gene expression. Apart from its high efficacy and speed, this programmable nuclease offers exceptional specificity with minimal off-target effects. Here in, we aim to review the latest findings on the application of the CRISPR/Cas9 genome editing tool for generating resilience in plants against environmental stresses.

A simplified and improved protocol of rice transformation to cater wide range of rice cultivars

The latest CRISPR-Cas9-mediated genome editing technology is expected to bring about revolution in rice yield and quality improvement, and thus validation of rice transformation protocols using CRISPR-Cas9-gRNA constructs is the need of the hour. Moreover, regeneration of more number of transgenic rice plants is prerequisite for developing genome-edited rice lines, as recalcitrant rice varieties were shown to have lower editing efficiencies which necessities screening of large number of transgenic plants to find the suitable edits. In the present study, we have simplified the Agrobacterium-mediated rice transformation protocol for both Indica and Japonica rice cultivars using CRISPR/Cas9 empty vector construct, and the protocols have been suitably optimized for getting large numbers of the regenerated plantlets within the shortest possible time. The Japonica transgenic lines were obtained within 65 days and for the Indica cultivars, it took about 76-78 days. We also obtained about 90% regeneration efficiency for both Japonica and Indica cultivars. The transformation efficiency was about 97% in the case of Japonica and 69-83% in the case of Indica rice cultivars. Furthermore, we screened the OsWRKY24 gene editing efficiency by transforming rice cultivars with CRISPR/Cas9 construct harbouring sgRNA against OsWRKY24 gene and found about 90% editing efficiency in Japonica rice cultivars, while 30% of the transformed Indica cultivars were found to be edited. This implicated the presence of a robust repair mechanism in the Indica rice cultivars.

Callus-specific CRISPR/Cas9 system to increase heritable gene mutations in maize

MAIN CONCLUSION

A callus-specific CRISPR/Cas9 (CSC) system with Cas9 gene driven by the promoters of ZmCTA1 and ZmPLTP reduces somatic mutations and improves the production of heritable mutations in maize. The CRISPR/Cas9 system, due to its editing accuracy, provides an excellent tool for crop genetic breeding. Nevertheless, the traditional design utilizing CRISPR/Cas9 with ubiquitous expression leads to an abundance of somatic mutations, thereby complicating the detection of heritable mutations. We constructed a callus-specific CRISPR/Cas9 (CSC) system using callus-specific promoters of maize Chitinase A1 and Phospholipid transferase protein (pZmCTA1 and pZmPLTP) to drive Cas9 expression, and the target gene chosen for this study was the bZIP transcription factor Opaque2 (O2). The CRISPR/Cas9 system driven by the maize Ubiquitin promoter (pZmUbi) was employed as a comparative control. Editing efficiency analysis based on high-throughput tracking of mutations (Hi-TOM) showed that the CSC systems generated more target gene mutations than the ubiquitously expressed CRISPR/Cas9 (UC) system in calli. Transgenic plants were generated for the CSC and UC systems. We found that the CSC systems generated fewer target gene mutations than the UC system in the T0 seedlings but reduced the influence of somatic mutations. Nearly 100% of mutations in the T1 generation generated by the CSC systems were derived from the T0 plants. Only 6.3-16.7% of T1 mutations generated by the UC system were from the T0 generation. Our results demonstrated that the CSC system consistently produced more stable, heritable mutants in the subsequent generation, suggesting its potential application across various crops to facilitate the genetic breeding of desired mutations.

CRISPR/Cas9 targeted mutations of OsDSG1 gene enhanced salt tolerance in rice

Salinization is one of the leading causes of arable land shrinkage and rice yield decline, recently. Therefore, developing and utilizing salt-tolerant rice varieties have been seen as a crucial and urgent strategy to reduce the effects of saline intrusion and protect food security worldwide. In the current study, the CRISPR/Cas9 system was utilized to induce targeted mutations in the coding sequence of the OsDSG1, a gene involved in the ubiquitination pathway and the regulation of biochemical reactions in rice. The CRISPR/Cas9-induced mutations of the OsDSG1 were generated in a local rice cultivar and the mutant inheritance was validated at different generations. The OsDSG1 mutant lines showed an enhancement in salt tolerance compared to wild type plants at both germination and seedling stages indicated by increases in plant height, root length, and total fresh weight as well as the total chlorophyll and relative water contents under the salt stress condition. In addition, lower proline and MDA contents were observed in mutant rice as compared to wild type plants in the presence of salt stress. Importantly, no effect on seed germination and plant growth parameters was recorded in the CRISRP/Cas9-induced mutant rice under the normal condition. This study again indicates the involvement of the OsDSG1 gene in the salt resistant mechanism in rice and provides a potential strategy to enhance the tolerance of local rice varieties to the salt stress.

CRISPR/Cas genome editing in plants: mechanisms, applications, and overcoming bottlenecks

The CRISPR/Cas systems have emerged as transformative tools for precisely manipulating plant genomes and enhancement. It has provided unparalleled applications from modifying the plant genomes to resistant enhancement. This review manuscript summarises the mechanism, application, and current challenges in the CRISPR/Cas genome editing technology. It addresses the molecular mechanisms of different Cas genes, elucidating their applications in various plants through crop improvement, disease resistance, and trait improvement. The advent of the CRISPR/Cas systems has enabled researchers to precisely modify plant genomes through gene knockouts, knock-ins, and gene expression modulation. Despite these successes, the CRISPR/Cas technology faces challenges, including off-target effects, Cas toxicity, and efficiency. In this manuscript, we also discuss these challenges and outline ongoing strategies employed to overcome these challenges, including the development of novel CRISPR/Cas variants with improved specificity and specific delivery methods for different plant species. The manuscript will conclude by addressing the future perspectives of the CRISPR/Cas technology in plants. Although this review manuscript is not conclusive, it aims to provide immense insights into the current state and future potential of CRISPR/Cas in sustainable and secure plant production.

Stress salinity in plants: New strategies to cope with in the foreseeable scenario

The excess of salts in soils causes stress in most plants, except for some halophytes that can tolerate higher levels of salinity. The excess of Na+ generates an ionic imbalance, reducing the K+ content and altering cellular metabolism, thus impacting in plant growth and development. Additionally, salinity in soil induces water stress due to osmotic effects and increments the production of reactive oxygen species (ROS) that affect the cellular structure, damaging membranes and proteins, and altering the electrochemical potential of H+, which directly affects nutrient absorption by membrane transporters. However, plants possess mechanisms to overcome the toxicity of the sodium ions, such as internalization into the vacuole or exclusion from the cell, synthesis of enzymes or protective compounds against ROS, and the synthesis of metabolites that help to regulate the osmotic potential of plants. Physiologic and molecular mechanisms of salinity tolerance in plants will be addressed in this review. Furthermore, a revision of strategies taken by researchers to confer salt stress tolerance on agriculturally important species are discussed. These strategies include conventional breeding and genetic engineering as transgenesis and genome editing by CRISPR/Cas9.

Breeding rice for yield improvement through CRISPR/Cas9 genome editing method: current technologies and examples

The impending climate change is threatening the rice productivity of the Asian subcontinent as instances of crop failures due to adverse abiotic and biotic stress factors are becoming common occurrences. CRISPR-Cas9 mediated genome editing offers a potential solution for improving rice yield as well as its stress adaptation. This technology allows modification of plant's genetic elements and is not dependent on foreign DNA/gene insertion for incorporating a particular trait. In this review, we have discussed various CRISPR-Cas9 mediated genome editing tools for gene knockout, gene knock-in, simultaneously disrupting multiple genes by multiplexing, base editing and prime editing the genes. The review here also presents how these genome editing technologies have been employed to improve rice productivity by directly targeting the yield related genes or by indirectly manipulating various abiotic and biotic stress responsive genes. Lately, many countries treat genome-edited crops as non-GMOs because of the absence of foreign DNA in the final product. Thus, genome edited rice plants with improved yield attributes and stress resilience are expected to be accepted by the public and solve food crisis of a major portion of the globe.

Supplementary Information

The online version contains supplementary material available at 10.1007/s12298-024-01423-y.

Progress and prospects in harnessing wild relatives for genetic enhancement of salt tolerance in rice

Salt stress is the second most devastating abiotic stress after drought and limits rice production globally. Genetic enhancement of salinity tolerance is a promising and cost-effective approach to achieve yield gains in salt-affected areas. Breeding for salinity tolerance is challenging because of the genetic complexity of the response of rice plants to salt stress, as it is governed by minor genes with low heritability and high G × E interactions. The involvement of numerous physiological and biochemical factors further complicates this complexity. The intensive selection and breeding efforts targeted towards the improvement of yield in the green-revolution era inadvertently resulted in the gradual disappearance of the loci governing salinity tolerance and a significant reduction in genetic variability among cultivars. The limited utilization of genetic resources and narrow genetic base of improved cultivars have resulted in a plateau in response to salinity tolerance in modern cultivars. Wild species are an excellent genetic resource for broadening the genetic base of domesticated rice. Exploiting novel genes of underutilized wild rice relatives to restore salinity tolerance loci eliminated during domestication can result in significant genetic gain in rice cultivars. Wild species of rice, Oryza rufipogon and Oryza nivara, have been harnessed in the development of a few improved rice varieties like Jarava and Chinsura Nona 2. Furthermore, increased access to sequence information and enhanced knowledge about the genomics of salinity tolerance in wild relatives has provided an opportunity for the deployment of wild rice accessions in breeding programs, while overcoming the cross-incompatibility and linkage drag barriers witnessed in wild hybridization. Pre-breeding is another avenue for building material that are ready for utilization in breeding programs. Efforts should be directed towards systematic collection, evaluation, characterization, and deciphering salt tolerance mechanisms in wild rice introgression lines and deploying untapped novel loci to improve salinity tolerance in rice cultivars. This review highlights the potential of wild relatives of Oryza to enhance tolerance to salinity, track the progress of work, and provide a perspective for future research.

RNAi-Mediated Suppression of OsBBTI5 Promotes Salt Stress Tolerance in Rice

This study explores the impact of RNAi in terms of selectively inhibiting the expression of the OsBBTI5 gene, with the primary objective of uncovering its involvement in the molecular mechanisms associated with salt tolerance in rice. OsBBTI5, belonging to the Bowman-Birk inhibitor (BBI) family gene, is known for its involvement in plant stress responses. The gene was successfully cloned from rice, exhibiting transcriptional self-activation in yeast. A yeast two-hybrid assay confirmed its specific binding to OsAPX2 (an ascorbate peroxidase gene). Transgenic OsBBTI5-RNAi plants displayed insensitivity to varying concentrations of 24-epibrassinolide in the brassinosteroid sensitivity assay. However, they showed reduced root and plant height at high concentrations (10 and 100 µM) of GA3 immersion. Enzyme activity assays revealed increased peroxidase (POD) and superoxide dismutase (SOD) activities and decreased malondialdehyde (MDA) content under 40-60 mM NaCl. Transcriptomic analysis indicated a significant upregulation of photosynthesis-related genes in transgenic plants under salt stress compared to the wild type. Notably, this study provides novel insights, suggesting that the BBI gene is part of the BR signaling pathway, and that OsBBTI5 potentially enhances stress tolerance in transgenic plants through interaction with the salt stress-related gene OsAPX2.

Molecular Mechanisms and Regulatory Pathways Underlying Drought Stress Response in Rice

Rice is a staple food for 350 million people globally. Its yield thus affects global food security. Drought is a serious environmental factor affecting rice growth. Alleviating the inhibition of drought stress is thus an urgent challenge that should be solved to enhance rice growth and yield. This review details the effects of drought on rice morphology, physiology, biochemistry, and the genes associated with drought stress response, their biological functions, and molecular regulatory pathways. The review further highlights the main future research directions to collectively provide theoretical support and reference for improving drought stress adaptation mechanisms and breeding new drought-resistant rice varieties.

CRISPR/Cas9-gene editing approaches in plant breeding

CRISPR/Cas9 gene editing system is recently developed robust genome editing technology for accelerating plant breeding. Various modifications of this editing system have been established for adaptability in plant varieties as well as for its improved efficiency and portability. This review provides an in-depth look at the various strategies for synthesizing gRNAs for efficient delivery in plant cells, including chemical synthesis and in vitro transcription. It also covers traditional analytical tools and emerging developments in detection methods to analyze CRISPR/Cas9 mediated mutation in plant breeding. Additionally, the review outlines the various analytical tools which are used to detect and analyze CRISPR/Cas9 mediated mutations, such as next-generation sequencing, restriction enzyme analysis, and southern blotting. Finally, the review discusses emerging detection methods, including digital PCR and qPCR. Hence, CRISPR/Cas9 has great potential for transforming agriculture and opening avenues for new advancements in the system for gene editing in plants.

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.

Smart reprograming of plants against salinity stress using modern biotechnological tools

Climate change gives rise to numerous environmental stresses, including soil salinity. Salinity/salt stress is the second biggest abiotic factor affecting agricultural productivity worldwide by damaging numerous physiological, biochemical, and molecular processes. In particular, salinity affects plant growth, development, and productivity. Salinity responses include modulation of ion homeostasis, antioxidant defense system induction, and biosynthesis of numerous phytohormones and osmoprotectants to protect plants from osmotic stress by decreasing ion toxicity and augmented reactive oxygen species scavenging. As most crop plants are sensitive to salinity, improving salt tolerance is crucial in sustaining global agricultural productivity. In response to salinity, plants trigger stress-related genes, proteins, and the accumulation of metabolites to cope with the adverse consequence of salinity. Therefore, this review presents an overview of salinity stress in crop plants. We highlight advances in modern biotechnological tools, such as omics (genomics, transcriptomics, proteomics, and metabolomics) approaches and different genome editing tools (ZFN, TALEN, and CRISPR/Cas system) for improving salinity tolerance in plants and accomplish the goal of "zero hunger," a worldwide sustainable development goal proposed by the FAO.

Advancements and prospects of CRISPR/Cas9 technologies for abiotic and biotic stresses in sugar beet

Sugar beet is a crop with high sucrose content, known for sugar production and recently being considered as an emerging raw material for bioethanol production. This crop is also utilized as cattle feed, mainly when animal green fodder is scarce. Bioethanol and hydrogen gas production from this crop is an essential source of clean energy. Environmental stresses (abiotic/biotic) severely affect the productivity of this crop. Over the past few decades, the molecular mechanisms of biotic and abiotic stress responses in sugar beet have been investigated using next-generation sequencing, gene editing/silencing, and over-expression approaches. This information can be efficiently utilized through CRISPR/Cas 9 technology to mitigate the effects of abiotic and biotic stresses in sugar beet cultivation. This review highlights the potential use of CRISPR/Cas 9 technology for abiotic and biotic stress management in sugar beet. Beet genes known to be involved in response to alkaline, cold, and heavy metal stresses can be precisely modified via CRISPR/Cas 9 technology for enhancing sugar beet's resilience to abiotic stresses with minimal off-target effects. Similarly, CRISPR/Cas 9 technology can help generate insect-resistant sugar beet varieties by targeting susceptibility-related genes, whereas incorporating Cry1Ab and Cry1C genes may provide defense against lepidopteron insects. Overall, CRISPR/Cas 9 technology may help enhance sugar beet's adaptability to challenging environments, ensuring sustainable, high-yield production.

Genetic Databases and Gene Editing Tools for Enhancing Crop Resistance against Abiotic Stress

Abiotic stresses extensively reduce agricultural crop production globally. Traditional breeding technology has been the fundamental approach used to cope with abiotic stresses. The development of gene editing technology for modifying genes responsible for the stresses and the related genetic networks has established the foundation for sustainable agriculture against environmental stress. Integrated approaches based on functional genomics and transcriptomics are now expanding the opportunities to elucidate the molecular mechanisms underlying abiotic stress responses. This review summarizes some of the features and weblinks of plant genome databases related to abiotic stress genes utilized for improving crops. The gene-editing tool based on clustered, regularly interspaced short palindromic repeats (CRISPR)/CRISPR-associated protein 9 (Cas9) has revolutionized stress tolerance research due to its simplicity, versatility, adaptability, flexibility, and broader applications. However, off-target and low cleavage efficiency hinder the successful application of CRISPR/Cas systems. Computational tools have been developed for designing highly competent gRNA with better cleavage efficiency. This powerful genome editing tool offers tremendous crop improvement opportunities, overcoming conventional breeding techniques' shortcomings. Furthermore, we also discuss the mechanistic insights of the CRISPR/Cas9-based genome editing technology. This review focused on the current advances in understanding plant species' abiotic stress response mechanism and applying the CRISPR/Cas system genome editing technology to develop crop resilience against drought, salinity, temperature, heavy metals, and herbicides.

Evidence and opportunities for developing non-transgenic genome edited crops using site-directed nuclease 1 approach

The innovations and progress in genome editing/new breeding technologies have revolutionized research in the field of functional genomics and crop improvement. This revolution has expanded the horizons of agricultural research, presenting fresh possibilities for creating novel plant varieties equipped with desired traits that can effectively combat the challenges posed by climate change. However, the regulation and social acceptance of genome-edited crops still remain as major barriers. Only a few countries considered the site-directed nuclease 1 (SDN1) approach-based genome-edited plants under less or no regulation. Hence, the present review aims to comprise information on the research work conducted using SDN1 in crops by various genome editing tools. It also elucidates the promising candidate genes that can be used for editing and has listed the studies on non-transgenic crops developed through SDN1 either by Agrobacterium-mediated transformation or by ribo nucleoprotein (RNP) complex. The review also hoards the existing regulatory landscape of genome editing and provides an overview of globally commercialized genome-edited crops. These compilations will enable confidence in researchers and policymakers, across the globe, to recognize the full potential of this technology and reconsider the regulatory aspects associated with genome-edited crops. Furthermore, this compilation serves as a valuable resource for researchers embarking on the development of customized non-transgenic crops through the utilization of SDN1.

Data-driven approaches to improve water-use efficiency and drought resistance in crop plants

With the increasing population, there lies a pressing demand for food, feed and fibre, while the changing climatic conditions pose severe challenges for agricultural production worldwide. Water is the lifeline for crop production; thus, enhancing crop water-use efficiency (WUE) and improving drought resistance in crop varieties are crucial for overcoming these challenges. Genetically-driven improvements in yield, WUE and drought tolerance traits can buffer the worst effects of climate change on crop production in dry areas. While traditional crop breeding approaches have delivered impressive results in increasing yield, the methods remain time-consuming and are often limited by the existing allelic variation present in the germplasm. Significant advances in breeding and high-throughput omics technologies in parallel with smart agriculture practices have created avenues to dramatically speed up the process of trait improvement by leveraging the vast volumes of genomic and phenotypic data. For example, individual genome and pan-genome assemblies, along with transcriptomic, metabolomic and proteomic data from germplasm collections, characterised at phenotypic levels, could be utilised to identify marker-trait associations and superior haplotypes for crop genetic improvement. In addition, these omics approaches enable the identification of genes involved in pathways leading to the expression of a trait, thereby providing an understanding of the genetic, physiological and biochemical basis of trait variation. These data-driven gene discoveries and validation approaches are essential for crop improvement pipelines, including genomic breeding, speed breeding and gene editing. Herein, we provide an overview of prospects presented using big data-driven approaches (including artificial intelligence and machine learning) to harness new genetic gains for breeding programs and develop drought-tolerant crop varieties with favourable WUE and high-yield potential traits.

CRISPR-Cas technology secures sustainability through its applications: a review in green biotechnology

The CRISPR-Cas system's applications in biotechnology offer a promising avenue for addressing pressing global challenges, such as climate change, environmental pollution, the energy crisis, and the food crisis, thereby advancing sustainability. The ever-growing demand for food due to the projected population of around 9.6 billion by 2050 requires innovation in agriculture. CRISPR-Cas technology emerges as a powerful solution, enhancing crop varieties, optimizing yields, and improving resilience to stressors. It offers multiple gene editing, base editing, and prime editing, surpassing conventional methods. CRISPR-Cas introduces disease and herbicide resistance, high-yielding, drought-tolerant, and water-efficient crops to address rising water utilization and to improve the efficiency of agricultural practices which promise food sustainability and revolutionize agriculture for the benefit of future generations. The application of CRISPR-Cas technology extends beyond agriculture to address environmental challenges. With the adverse impacts of climate change and pollution endangering ecosystems, there is a growing need for sustainable solutions. The technology's potential in carbon capture and reduction through bio-sequestration is a pivotal strategy for combating climate change. Genomic advancements allow for the development of genetically modified organisms, optimizing biofuel and biomaterial production, and contributing to a renewable and sustainable energy future. This study reviews the multifaceted applications of CRISPR-Cas technology in the agricultural and environmental fields and emphasizes its potential to secure a sustainable future.

Plant breeding for harmony between sustainable agriculture, the environment, and global food security: an era of genomics-assisted breeding

MAIN CONCLUSION

Genomics-assisted breeding represents a crucial frontier in enhancing the balance between sustainable agriculture, environmental preservation, and global food security. Its precision and efficiency hold the promise of developing resilient crops, reducing resource utilization, and safeguarding biodiversity, ultimately fostering a more sustainable and secure food production system. Agriculture has been seriously threatened over the last 40 years by climate changes that menace global nutrition and food security. Changes in environmental factors like drought, salt concentration, heavy rainfalls, and extremely low or high temperatures can have a detrimental effects on plant development, growth, and yield. Extreme poverty and increasing food demand necessitate the need to break the existing production barriers in several crops. The first decade of twenty-first century marks the rapid development in the discovery of new plant breeding technologies. In contrast, in the second decade, the focus turned to extracting information from massive genomic frameworks, speculating gene-to-phenotype associations, and producing resilient crops. In this review, we will encompass the causes, effects of abiotic stresses and how they can be addressed using plant breeding technologies. Both conventional and modern breeding technologies will be highlighted. Moreover, the challenges like the commercialization of biotechnological products faced by proponents and developers will also be accentuated. The crux of this review is to mention the available breeding technologies that can deliver crops with high nutrition and climate resilience for sustainable agriculture.

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.

Genetic modification strategies for enhancing plant resilience to abiotic stresses in the context of climate change

Enhancing the resilience of plants to abiotic stresses, such as drought, salinity, heat, and cold, is crucial for ensuring global food security challenge in the context of climate change. The adverse effects of climate change, characterized by rising temperatures, shifting rainfall patterns, and increased frequency of extreme weather events, pose significant threats to agricultural systems worldwide. Genetic modification strategies offer promising approaches to develop crops with improved abiotic stress tolerance. This review article provides a comprehensive overview of various genetic modification techniques employed to enhance plant resilience. These strategies include the introduction of stress-responsive genes, transcription factors, and regulatory elements to enhance stress signaling pathways. Additionally, the manipulation of hormone signaling pathways, osmoprotectant accumulation, and antioxidant defense mechanisms is discussed. The use of genome editing tools, such as CRISPR-Cas9, for precise modification of target genes related to stress tolerance is also explored. Furthermore, the challenges and future prospects of genetic modification for abiotic stress tolerance are highlighted. Understanding and harnessing the potential of genetic modification strategies can contribute to the development of resilient crop varieties capable of withstanding adverse environmental conditions caused by climate change, thereby ensuring sustainable agricultural productivity and food security.

Recent Developments in CRISPR/Cas9 Genome-Editing Technology Related to Plant Disease Resistance and Abiotic Stress Tolerance

The revolutionary CRISPR/Cas9 genome-editing technology has emerged as a powerful tool for plant improvement, offering unprecedented precision and efficiency in making targeted gene modifications. This powerful and practical approach to genome editing offers tremendous opportunities for crop improvement, surpassing the capabilities of conventional breeding techniques. This article provides an overview of recent advancements and challenges associated with the application of CRISPR/Cas9 in plant improvement. The potential of CRISPR/Cas9 in terms of developing crops with enhanced resistance to biotic and abiotic stresses is highlighted, with examples of genes edited to confer disease resistance, drought tolerance, salt tolerance, and cold tolerance. Here, we also discuss the importance of off-target effects and the efforts made to mitigate them, including the use of shorter single-guide RNAs and dual Cas9 nickases. Furthermore, alternative delivery methods, such as protein- and RNA-based approaches, are explored, and they could potentially avoid the integration of foreign DNA into the plant genome, thus alleviating concerns related to genetically modified organisms (GMOs). We emphasize the significance of CRISPR/Cas9 in accelerating crop breeding processes, reducing editing time and costs, and enabling the introduction of desired traits at the nucleotide level. As the field of genome editing continues to evolve, it is anticipated that CRISPR/Cas9 will remain a prominent tool for crop improvement, disease resistance, and adaptation to challenging environmental conditions.

Genome Editing and Improvement of Abiotic Stress Tolerance in Crop Plants

Genome editing aims to revolutionise plant breeding and could assist in safeguarding the global food supply. The inclusion of a 12-40 bp recognition site makes mega nucleases the first tools utilized for genome editing and first generation gene-editing tools. Zinc finger nucleases (ZFNs) are the second gene-editing technique, and because they create double-stranded breaks, they are more dependable and effective. ZFNs were the original designed nuclease-based approach of genome editing. The Cys2-His2 zinc finger domain's discovery made this technique possible. Clustered regularly interspaced short palindromic repeats (CRISPR) are utilized to improve genetics, boost biomass production, increase nutrient usage efficiency, and develop disease resistance. Plant genomes can be effectively modified using genome-editing technologies to enhance characteristics without introducing foreign DNA into the genome. Next-generation plant breeding will soon be defined by these exact breeding methods. There is abroad promise that genome-edited crops will be essential in the years to come for improving the sustainability and climate-change resilience of food systems. This method also has great potential for enhancing crops' resistance to various abiotic stressors. In this review paper, we summarize the most recent findings about the mechanism of abiotic stress response in crop plants and the use of the CRISPR/Cas mediated gene-editing systems to improve tolerance to stresses including drought, salinity, cold, heat, and heavy metals.

Enhancing Crop Resilience to Drought Stress through CRISPR-Cas9 Genome Editing

With increasing frequency and severity of droughts in various parts of the world, agricultural productivity may suffer major setbacks. Among all the abiotic factors, drought is likely to have one of the most detrimental effects on soil organisms and plants. Drought is a major problem for crops because it limits the availability of water, and consequently nutrients which are crucial for plant growth and survival. This results in reduced crop yields, stunted growth, and even plant death, according to the severity and duration of the drought, the plant's developmental stage, and the plant's genetic background. The ability to withstand drought is a highly complex characteristic that is controlled by multiple genes, making it one of the most challenging attributes to study, classify, and improve. Clustered Regularly Interspaced Short Palindromic Repeat (CRISPR) technology has opened a new frontier in crop enhancement, revolutionizing plant molecular breeding. The current review provides a general understanding of principles as well as optimization of CRISPR system, and presents applications on genetic enhancement of crops, specifically in terms of drought resistance and yield. Moreover, we discuss how innovative genome editing techniques can aid in the identification and modification of genes conferring drought tolerance.

The Potential of CRISPR/Cas Technology to Enhance Crop Performance on Adverse Soil Conditions

Worldwide food security is under threat in the actual scenery of global climate change because the major staple food crops are not adapted to hostile climatic and soil conditions. Significant efforts have been performed to maintain the actual yield of crops, using traditional breeding and innovative molecular techniques to assist them. However, additional strategies are necessary to achieve the future food demand. Clustered regularly interspaced short palindromic repeat/CRISPR-associated protein (CRISPR/Cas) technology, as well as its variants, have emerged as alternatives to transgenic plant breeding. This novelty has helped to accelerate the necessary modifications in major crops to confront the impact of abiotic stress on agriculture systems. This review summarizes the current advances in CRISPR/Cas applications in crops to deal with the main hostile soil conditions, such as drought, flooding and waterlogging, salinity, heavy metals, and nutrient deficiencies. In addition, the potential of extremophytes as a reservoir of new molecular mechanisms for abiotic stress tolerance, as well as their orthologue identification and edition in crops, is shown. Moreover, the future challenges and prospects related to CRISPR/Cas technology issues, legal regulations, and customer acceptance will be discussed.

Functions and interaction of plant lipid signalling under abiotic stresses

Lipids are the primary form of energy storage and a major component of plasma membranes, which form the interface between the cell and the extracellular environment. Several lipids - including phosphoinositide, phosphatidic acid, sphingolipids, lysophospholipids, oxylipins, and free fatty acids - also serve as substrates for the generation of signalling molecules. Abiotic stresses, such as drought and temperature stress, are known to affect plant growth. In addition, abiotic stresses can activate certain lipid-dependent signalling pathways that control the expression of stress-responsive genes and contribute to plant stress adaptation. Many studies have focused either on the enzymatic production and metabolism of lipids, or on the mechanisms of abiotic stress response. However, there is little information regarding the roles of plant lipids in plant responses to abiotic stress. In this review, we describe the metabolism of plant lipids and discuss their involvement in plant responses to abiotic stress. As such, this review provides crucial background for further research on the interactions between plant lipids and abiotic stress.

Can the Wild Perennial, Rhizomatous Rice Species Oryza longistaminata be a Candidate for De Novo Domestication?

As climate change intensifies, the development of resilient rice that can tolerate abiotic stresses is urgently needed. In nature, many wild plants have evolved a variety of mechanisms to protect themselves from environmental stresses. Wild relatives of rice may have abundant and virtually untapped genetic diversity and are an essential source of germplasm for the improvement of abiotic stress tolerance in cultivated rice. Unfortunately, the barriers of traditional breeding approaches, such as backcrossing and transgenesis, make it challenging and complex to transfer the underlying resilience traits between plants. However, de novo domestication via genome editing is a quick approach to produce rice with high yields from orphans or wild relatives. African wild rice, Oryza longistaminata, which is part of the AA-genome Oryza species has two types of propagation strategies viz. vegetative propagation via rhizome and seed propagation. It also shows tolerance to multiple types of abiotic stress, and therefore O. longistaminata is considered a key candidate of wild rice for heat, drought, and salinity tolerance, and it is also resistant to lodging. Importantly, O. longistaminata is perennial and propagates also via rhizomes both of which are traits that are highly valuable for the sustainable production of rice. Therefore, O. longistaminata may be a good candidate for de novo domestication through genome editing to obtain rice that is more climate resilient than modern elite cultivars of O. sativa.

Tissue Culture—A Sustainable Approach to Explore Plant Stresses

Plants are constantly faced with biotic or abiotic stress, which affects their growth and development. Yield reduction due to biotic and abiotic stresses on economically important crop species causes substantial economic loss at a global level. Breeding for stress tolerance to create elite and superior genotypes has been a common practice for many decades, and plant tissue culture can be an efficient and cost-effective method. Tissue culture is a valuable tool to develop stress tolerance, screen stress tolerance, and elucidate physiological and biochemical changes during stress. In vitro selection carried out under controlled environment conditions in confined spaces is highly effective and cheaper to maintain. This review emphasizes the relevance of plant tissue culture for screening major abiotic stresses, drought, and salinity, and the development of disease resistance. Further emphasis is given to screening metal hyperaccumulators and transgenic technological applications for stress tolerance.

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.

Plant breeding advancements with "CRISPR-Cas" genome editing technologies will assist future food security

Genome editing techniques are being used to modify plant breeding, which might increase food production sustainably by 2050. A product made feasible by genome editing is becoming better known, because of looser regulation and widespread acceptance. The world's population and food supply would never have increased proportionally under current farming practices. The development of plants and food production has been greatly impacted by global warming and climate change. Therefore, minimizing these effects is crucial for agricultural production that is sustainable. Crops are becoming more resilient to abiotic stress because of sophisticated agricultural practices and a better understanding of the abiotic stress response mechanism. Both conventional and molecular breeding techniques have been used to create viable crop types both processes are time-consuming. Recently, plant breeders have shown an interest in genome editing approaches for genetic manipulation that use clustered regularly interspaced short palindromic repeats (CRISPR/Cas9). To ensure the security of the food supply in the future, plant kinds with desired traits must be developed. A completely new era in plant breeding has begun because of the revolution in genome editing techniques based on the CRISPR/CRISPR-associated nuclease (Cas9) systems. All plants may effectively target a particular gene or group of loci using Cas9 and single-guide RNA (sgRNA). CRISPR/Cas9 can thereby save time and labor compared to conventional breeding methods. An easy, quick, and efficient method for directly altering the genetic sequences in cells is with the CRISPR and Cas9 systems. The CRISPR-Cas9 system, which was developed from components of the earliest known bacterial immune system, allows for targeted gene breakage and gene editing in a variety of cells/RNA sequences to guide endonuclease cleavage specificity in the CRISPR-Cas9 system. Editing can be directed to practically any genomic site by altering the guide RNA (gRNA) sequence and delivering it to a target cell along with the Cas9 endonuclease. We summarize recent CRISPR/Cas9 plant research findings, investigate potential applications in plant breeding, and make predictions about likely future breakthroughs and approaches to food security through 2050.

Improvement of Salinity Tolerance in Water-Saving and Drought-Resistance Rice (WDR)

Rice is one of the most economically important staple food crops in the world. Soil salinization and drought seriously restrict sustainable rice production. Drought aggravates the degree of soil salinization, and, at the same time, increased soil salinity also inhibits water absorption, resulting in physiological drought stress. Salt tolerance in rice is a complex quantitative trait controlled by multiple genes. This review presents and discusses the recent research developments on salt stress impact on rice growth, rice salt tolerance mechanisms, the identification and selection of salt-tolerant rice resources, and strategies to improve rice salt tolerance. In recent years, the increased cultivation of water-saving and drought-resistance rice (WDR) has shown great application potential in alleviating the water resource crisis and ensuring food and ecological security. Here, we present an innovative germplasm selection strategy of salt-tolerant WDR, using a population that is developed by recurrent selection based on dominant genic male sterility. We aim to provide a reference for efficient genetic improvement and germplasm innovation of complex traits (drought and salt tolerance) that can be translated into breeding all economically important cereal crops.

The suppressed expression of a stress responsive gene 'OsDSR2' enhances rice tolerance in drought and salt stress

Rice is a crucial staple food crop in many countries, yet, abiotic factors like salt and drought impact its growth. The Domain of Unknown Function 966 (DUF966) gene family may be crucial in how rice plants respond to abiotic stress. Our earlier research showed that overexpression of OsDSR2 (DUF966-stress repressive gene 2 in Oryza sativa) decreased resistance to salt and drought stress. To further understand how OsDSR2 negatively affects rice tolerance to salt and drought stress, transgenic rice plants with decreased OsDSR2 expression levels were created employing the RNAi technique. We investigated alterations in rice phenotype, physiology, and differentially expressed genes (DEGs) using a combination of physio-biochemical measurement and RNA-seq analysis. The results of the study demonstrated that rice seedling lines with OsDSR2 knockdown exhibited improved salt and drought stress tolerance. Statistical analysis revealed that the transgenic plants' survival rate (56-68%) was higher than the control plants (30%), in addition to a roughly 3 fold, 3.5 fold, 20% and 10.5% reduction in cell membrane permeability, malondialdehyde (MDA), superoxide anion radical (O₂^-) and hydrogen peroxide (H₂O₂) contents, respectively. However, the proline content and antioxidant enzymes (superoxide dismutase (SOD) and peroxidase (POD)) activities were considerably increased by about 5.5 fold, 3.5 fold, and 4.5 fold, respectively, at physiological levels. There were 115 up-regulated and 173 down-regulated DEGs in the leaves of the transgenic lines on the transcriptional regulation under the combined salt-drought stress. Among these, both up-regulation DEGs (e.g., OsHAK5, OsIAA25) and the down-regulation DEGs (e.g., OsbZIP23, OsERF48, OsAP2-39, etc.) may be related to the enhanced tolerance of the transgenic lines under combined salt-drought stress. This possibly depended on the involvement of abscisic acid (ABA) and indoleacetic acid (IAA) signaling pathways. These findings further confirmed that OsDSR2 negatively affected rice's ability to withstand salt and drought, suggesting that it could be a helpful gene for CRISPR-Cas9 technology-based genetic modification of rice's ability to withstand abiotic stress.

CRISPR/Cas genome editing in plants: Dawn of Agrobacterium transformation for recalcitrant and transgene-free plants for future crop breeding

Genome editing tools based on CRISPR/Cas system have been posed to solve many issues in agriculture and improve food production. Genetic engineering by Agrobacterium-mediated transformation has helped to impart specific traits straightaway in many crops. Many GM crops have also reached the field for commercial cultivation. Genetic engineering requires mostly a transformation protocol often mediated by Agrobacterium to insert a specific gene at a random locus. Genome editing with CRISPR/Cas system is a more precise technique for the targeted modification of genes/bases in the host plant genome. Unlike the conventional transformation system, wherein elimination of marker/foreign gene was possible only post-transformation, CRISPR/Cas system could generate transgene-free plants by delivering CRISPR/Cas reagents such as the Cas protein and guide RNAs gRNA(s) preassembled to form ribonucleoproteins (RNPs) into plant cells. CRISPR reagent delivery might be helpful to overcome issues with plants that are recalcitrant to Agrobacterium transformation and the legal hurdles due to the presence of the foreign gene. More recently, the grafting of wild-type shoots to transgenic donor rootstocks developed by the CRISPR/Cas system has reported transgene-free genome editing. CRISPR/Cas system also requires only a small piece of gRNA besides Cas9 or other effectors to target a specific region in the genome. So this system has been projected to be a key contributor to future crop breeding. In this article, we recap the main events of plant transformation, compare the difference between genetic transformation and CRISPR/Cas-mediated genome editing, and draw insights into the future application of the CRISPR/Cas system.

Improving abiotic stress tolerance of forage grasses - prospects of using genome editing

Due to an increase in the consumption of food, feed, and fuel and to meet global food security needs for the rapidly growing human population, there is a necessity to obtain high-yielding crops that can adapt to future climate changes. Currently, the main feed source used for ruminant livestock production is forage grasses. In temperate climate zones, perennial grasses grown for feed are widely distributed and tend to suffer under unfavorable environmental conditions. Genome editing has been shown to be an effective tool for the development of abiotic stress-resistant plants. The highly versatile CRISPR-Cas system enables increasingly complex modifications in genomes while maintaining precision and low off-target frequency mutations. In this review, we provide an overview of forage grass species that have been subjected to genome editing. We offer a perspective view on the generation of plants resilient to abiotic stresses. Due to the broad factors contributing to these stresses the review focuses on drought, salt, heat, and cold stresses. The application of new genomic techniques (e.g., CRISPR-Cas) allows addressing several challenges caused by climate change and abiotic stresses for developing forage grass cultivars with improved adaptation to the future climatic conditions. Genome editing will contribute towards developing safe and sustainable food systems.

Gene Editing for Plant Resistance to Abiotic Factors: A Systematic Review

Agricultural crops are exposed to various abiotic stresses, such as salinity, water deficits, temperature extremes, floods, radiation, and metal toxicity. To overcome these challenges, breeding programs seek to improve methods and techniques. Gene editing by Clustered Regularly Interspaced Short Palindromic Repeats-CRISPR/Cas-is a versatile tool for editing in all layers of the central dogma with focus on the development of cultivars of plants resistant or tolerant to multiple biotic or abiotic stresses. This systematic review (SR) brings new contributions to the study of the use of CRISPR/Cas in gene editing for tolerance to abiotic stress in plants. Articles deposited in different electronic databases, using a search string and predefined inclusion and exclusion criteria, were evaluated. This SR demonstrates that the CRISPR/Cas system has been applied to several plant species to promote tolerance to the main abiotic stresses. Among the most studied crops are rice and Arabidopsis thaliana, an important staple food for the population, and a model plant in genetics/biotechnology, respectively, and more recently tomato, whose number of studies has increased since 2021. Most studies were conducted in Asia, specifically in China. The Cas9 enzyme is used in most articles, and only Cas12a is used as an additional gene editing tool in plants. Ribonucleoproteins (RNPs) have emerged as a DNA-free strategy for genome editing without exogenous DNA. This SR also identifies several genes edited by CRISPR/Cas, and it also shows that plant responses to stress factors are mediated by many complex-signaling pathways. In addition, the quality of the articles included in this SR was validated by a risk of bias analysis. The information gathered in this SR helps to understand the current state of CRISPR/Cas in the editing of genes and noncoding sequences, which plays a key role in the regulation of various biological processes and the tolerance to multiple abiotic stresses, with potential for use in plant genetic improvement programs.

Application of CRISPR/Cas9-mediated gene editing for abiotic stress management in crop plants

Abiotic stresses, including drought, salinity, cold, heat, and heavy metals, extensively reducing global agricultural production. Traditional breeding approaches and transgenic technology have been widely used to mitigate the risks of these environmental stresses. The discovery of engineered nucleases as genetic scissors to carry out precise manipulation in crop stress-responsive genes and associated molecular network has paved the way for sustainable management of abiotic stress conditions. In this context, the clustered regularly interspaced short palindromic repeat-Cas (CRISPR/Cas)-based gene-editing tool has revolutionized due to its simplicity, accessibility, adaptability, flexibility, and wide applicability. This system has great potential to build up crop varieties with enhanced tolerance against abiotic stresses. In this review, we summarize the latest findings on understanding the mechanism of abiotic stress response in plants and the application of CRISPR/Cas-mediated gene-editing system towards enhanced tolerance to a multitude of stresses including drought, salinity, cold, heat, and heavy metals. We provide mechanistic insights on the CRISPR/Cas9-based genome editing technology. We also discuss applications of evolving genome editing techniques such as prime editing and base editing, mutant library production, transgene free and multiplexing to rapidly deliver modern crop cultivars adapted to abiotic stress conditions.

The role of metal transporters in phytoremediation: A closer look at Arabidopsis

Pollution of the environment by heavy metals (HMs) has recently become a global issue, affecting the health of all living organisms. Continuous human activities (industrialization and urbanization) are the major causes of HM release into the environment. Over the years, two methods (physical and chemical) have been widely used to reduce HMs in polluted environment. However, these two methods are inefficient and very expensive to reduce the HMs released into the atmosphere. Alternatively, researchers are trying to remove the HMs by employing hyper-accumulator plants. This method, referred to phytoremediation, is highly efficient, cost-effective, and eco-friendly. Phytoremediation can be divided into five types: phytostabilization, phytodegradation, rhizofiltration, phytoextraction, and phytovolatilization, all of which contribute to HMs removal from the polluted environment. Brassicaceae family members (particularly Arabidopsis thaliana) can accumulate more HMs from the contaminated environment than those of other plants. This comprehensive review focuses on how HMs pollute the environment and discusses the phytoremediation measures required to reduce the impact of HMs on the environment. We discuss the role of metal transporters in phytoremediation with a focus on Arabidopsis. Then draw insights into the role of genome editing tools in enhancing phytoremediation efficiency. This review is expected to initiate further research to improve phytoremediation by biotechnological approaches to conserve the environment from pollution.

CRISPR/Cas Genome Editing Technologies for Plant Improvement against Biotic and Abiotic Stresses: Advances, Limitations, and Future Perspectives

Crossbreeding, mutation breeding, and traditional transgenic breeding take much time to improve desirable characters/traits. CRISPR/Cas-mediated genome editing (GE) is a game-changing tool that can create variation in desired traits, such as biotic and abiotic resistance, increase quality and yield in less time with easy applications, high efficiency, and low cost in producing the targeted edits for rapid improvement of crop plants. Plant pathogens and the severe environment cause considerable crop losses worldwide. GE approaches have emerged and opened new doors for breeding multiple-resistance crop varieties. Here, we have summarized recent advances in CRISPR/Cas-mediated GE for resistance against biotic and abiotic stresses in a crop molecular breeding program that includes the modification and improvement of genes response to biotic stresses induced by fungus, virus, and bacterial pathogens. We also discussed in depth the application of CRISPR/Cas for abiotic stresses (herbicide, drought, heat, and cold) in plants. In addition, we discussed the limitations and future challenges faced by breeders using GE tools for crop improvement and suggested directions for future improvements in GE for agricultural applications, providing novel ideas to create super cultivars with broad resistance to biotic and abiotic stress.

USDA's revised biotechnology regulation's contribution to increasing agricultural sustainability and responding to climate change

Biotechnology can provide a valuable tool to meet UN Sustainable Development Goals and U.S. initiatives to find climate solutions and improve agricultural sustainability. The literature contains hundreds of examples of crops that may serve this purpose, yet most remain un-launched due to high regulatory barriers. Recently the USDA revised its biotechnology regulations to make them more risk-proportionate, science-based, and streamlined. Here, we review some of the promising leads that may enable agriculture to contribute to UN sustainability goals. We further describe and discuss how the revised biotechnology regulation would hypothetically apply to these cases.

Engineering drought and salinity tolerance traits in crops through CRISPR-mediated genome editing: Targets, tools, challenges, and perspectives

Prolonged periods of drought triggered by climate change hamper plant growth and cause substantial agricultural yield losses every year. In addition to drought, salinity is one of the major abiotic stresses that severely affect crop health and agricultural production. Plant responses to drought and salinity involve multiple processes that operate in a spatiotemporal manner, such as stress sensing, perception, epigenetic modifications, transcription, post-transcriptional processing, translation, and post-translational changes. Consequently, drought and salinity stress tolerance are polygenic traits influenced by genome-environment interactions. One of the ideal solutions to these challenges is the development of high-yielding crop varieties with enhanced stress tolerance, together with improved agricultural practices. Recently, genome-editing technologies, especially clustered regularly interspaced short palindromic repeats (CRISPR) tools, have been effectively applied to elucidate how plants deal with drought and saline environments. In this work, we aim to portray that the combined use of CRISPR-based genome engineering tools and modern genomic-assisted breeding approaches are gaining momentum in identifying genetic determinants of complex traits for crop improvement. This review provides a synopsis of plant responses to drought and salinity stresses at the morphological, physiological, and molecular levels. We also highlight recent advances in CRISPR-based tools and their use in understanding the multi-level nature of plant adaptations to drought and salinity stress. Integrating CRISPR tools with modern breeding approaches is ideal for identifying genetic factors that regulate plant stress-response pathways and for the introgression of beneficial traits to develop stress-resilient crops.

Engineering Abiotic Stress Tolerance in Crop Plants through CRISPR Genome Editing

Environmental abiotic stresses challenge food security by depressing crop yields often exceeding 50% of their annual production. Different methods, including conventional as well as genomic-assisted breeding, mutagenesis, and genetic engineering have been utilized to enhance stress resilience in several crop species. Plant breeding has been partly successful in developing crop varieties against abiotic stresses owning to the complex genetics of the traits as well as the narrow genetic base in the germplasm. Irrespective of the fact that genetic engineering can transfer gene(s) from any organism(s), transgenic crops have become controversial mainly due to the potential risk of transgene-outcrossing. Consequently, the cultivation of transgenic crops is banned in certain countries, particularly in European countries. In this scenario, the discovery of the CRISPR tool provides a platform for producing transgene-free genetically edited plants-similar to the mutagenized crops that are not extensively regulated such as genetically modified organisms (GMOs). Thus, the genome-edited plants without a transgene would likely go into the field without any restriction. Here, we focused on the deployment of CRISPR for the successful development of abiotic stress-tolerant crop plants for sustaining crop productivity under changing environments.

Application of CRISPR/Cas system in cereal improvement for biotic and abiotic stress tolerance

Application of the recently developed CRISPR/Cas tools might help enhance cereals' growth and yield under biotic and abiotic stresses. Cereals are the most important food crops for human life and an essential source of nutrients for people in developed and developing countries. The growth and yield of all major cereals are affected by both biotic and abiotic stresses. To date, molecular breeding and functional genomic studies have contributed to the understanding and improving cereals' growth and yield under biotic and abiotic stresses. Clustered, regularly inter-spaced, short palindromic repeats (CRISPR)/CRISPR-associated protein (Cas) system has been predicted to play a major role in precision plant breeding and developing non-transgenic cereals that can tolerate adverse effects of climate change. Variants of next-generation CRISPR/Cas tools, such as prime editor, base editor, CRISPR activator and repressor, chromatin imager, Cas12a, and Cas12b, are currently used in various fields, including plant science. However, few studies have been reported on applying the CRISPR/Cas system to understand the mechanism of biotic and abiotic stress tolerance in cereals. Rice is the only plant used frequently for such studies. Genes responsible for biotic and abiotic stress tolerance have not yet been studied by CRISPR/Cas system in other major cereals (sorghum, barley, maize and small millets). Examining the role of genes that respond to biotic and abiotic stresses using the CRISPR/Cas system may help enhance cereals' growth and yield under biotic and abiotic stresses. It will help to develop new and improved cultivars with biotic- and abiotic-tolerant traits for better yields to strengthen food security. This review provides information for cereal researchers on the current status of the CRISPR/Cas system for improving biotic and abiotic stress tolerance in cereals.

Genomics and transcriptomics to protect rice (Oryza sativa. L.) from abiotic stressors: -pathways to achieving zero hunger

More over half of the world's population depends on rice as a major food crop. Rice (Oryza sativa L.) is vulnerable to abiotic challenges including drought, cold, and salinity since it grown in semi-aquatic, tropical, or subtropical settings. Abiotic stress resistance has bred into rice plants since the earliest rice cultivation techniques. Prior to the discovery of the genome, abiotic stress-related genes were identified using forward genetic methods, and abiotic stress-tolerant lines have developed using traditional breeding methods. Dynamic transcriptome expression represents the degree of gene expression in a specific cell, tissue, or organ of an individual organism at a specific point in its growth and development. Transcriptomics can reveal the expression at the entire genome level during stressful conditions from the entire transcriptional level, which can be helpful in understanding the intricate regulatory network relating to the stress tolerance and adaptability of plants. Rice (Oryza sativa L.) gene families found comparatively using the reference genome sequences of other plant species, allowing for genome-wide identification. Transcriptomics via gene expression profiling which have recently dominated by RNA-seq complements genomic techniques. The identification of numerous important qtl,s genes, promoter elements, transcription factors and miRNAs involved in rice response to abiotic stress was made possible by all of these genomic and transcriptomic techniques. The use of several genomes and transcriptome methodologies to comprehend rice (Oryza sativa, L.) ability to withstand abiotic stress have been discussed in this review.

Biotechnological Advances to Improve Abiotic Stress Tolerance in Crops

The major challenges that agriculture is facing in the twenty-first century are increasing droughts, water scarcity, flooding, poorer soils, and extreme temperatures due to climate change. However, most crops are not tolerant to extreme climatic environments. The aim in the near future, in a world with hunger and an increasing population, is to breed and/or engineer crops to tolerate abiotic stress with a higher yield. Some crop varieties display a certain degree of tolerance, which has been exploited by plant breeders to develop varieties that thrive under stress conditions. Moreover, a long list of genes involved in abiotic stress tolerance have been identified and characterized by molecular techniques and overexpressed individually in plant transformation experiments. Nevertheless, stress tolerance phenotypes are polygenetic traits, which current genomic tools are dissecting to exploit their use by accelerating genetic introgression using molecular markers or site-directed mutagenesis such as CRISPR-Cas9. In this review, we describe plant mechanisms to sense and tolerate adverse climate conditions and examine and discuss classic and new molecular tools to select and improve abiotic stress tolerance in major crops.

Multiplex CRISPR/Cas9-mediated genome editing to address drought tolerance in wheat

Genome editing tools have rapidly been adopted by plant scientists for crop improvement. Genome editing using a multiplex sgRNA-CRISPR/Cas9 genome editing system is a useful technique for crop improvement in monocot species. In this study, we utilized precise gene editing techniques to generate wheat 3'(2'), 5'-bisphosphate nucleotidase (TaSal1) mutants using a multiplex sgRNA-CRISPR/Cas9 genome editing system. Five active TaSal1 homologous genes were found in the genome of Giza168 in addition to another apparently inactive gene on chromosome 4A. Three gRNAs were designed and used to target exons 4, 5 and 7 of the five wheat TaSal1 genes. Among the 120 Giza168 transgenic plants, 41 lines exhibited mutations and produced heritable TaSal1 mutations in the M1 progeny and 5 lines were full 5 gene knock-outs. These mutant plants exhibit a rolled-leaf phenotype in young leaves and bended stems, but there were no significant changes in the internode length and width, leaf morphology, and stem shape. Anatomical and scanning electron microscope studies of the young leaves of mutated TaSal1 lines showed closed stomata, increased stomata width and increase in the size of the bulliform cells. Sal1 mutant seedlings germinated and grew better on media containing polyethylene glycol than wildtype seedlings. Our results indicate that the application of the multiplex sgRNA-CRISPR/Cas9 genome editing is efficient tool for mutating more multiple TaSal1 loci in hexaploid wheat.

CRISPR/Cas9 Technology and Its Utility for Crop Improvement

The rapid growth of the global population has resulted in a considerable increase in the demand for food crops. However, traditional crop breeding methods will not be able to satisfy the worldwide demand for food in the future. New gene-editing technologies, the most widely used of which is CRISPR/Cas9, may enable the rapid improvement of crop traits. Specifically, CRISPR/Cas9 genome-editing technology involves the use of a guide RNA and a Cas9 protein that can cleave the genome at specific loci. Due to its simplicity and efficiency, the CRISPR/Cas9 system has rapidly become the most widely used tool for editing animal and plant genomes. It is ideal for modifying the traits of many plants, including food crops, and for creating new germplasm materials. In this review, the development of the CRISPR/Cas9 system, the underlying mechanism, and examples of its use for editing genes in important crops are discussed. Furthermore, certain limitations of the CRISPR/Cas9 system and potential solutions are described. This article will provide researchers with important information regarding the use of CRISPR/Cas9 gene-editing technology for crop improvement, plant breeding, and gene functional analyses.

CRISPR/Cas genome editing improves abiotic and biotic stress tolerance of crops

Abiotic stress such as cold, drought, saline-alkali stress and biotic stress including disease and insect pest are the main factors that affect plant growth and limit agricultural productivity. In recent years, with the rapid development of molecular biology, genome editing techniques have been widely used in botany and agronomy due to their characteristics of high efficiency, controllable and directional editing. Genome editing techniques have great application potential in breeding resistant varieties. These techniques have achieved remarkable results in resistance breeding of important cereal crops (such as maize, rice, wheat, etc.), vegetable and fruit crops. Among them, CRISPR/Cas (clustered regularly interspaced short palindromic repeats/CRISPR-associated) provides a guarantee for the stability of crop yield worldwide. In this paper, the development of CRISRR/Cas and its application in different resistance breeding of important crops are reviewed, the advantages and importance of CRISRR/Cas technology in breeding are emphasized, and the possible problems are pointed out.

Epigenetic marks for mitigating abiotic stresses in plants

Abiotic stressors are one of the major factors affecting agricultural output. Plants have evolved adaptive systems to respond appropriately to various environmental cues. These responses can be accomplished by modulating or fine-tuning genetic and epigenetic regulatory mechanisms. Understanding the response of plants' molecular features to abiotic stress is a priority in the current period of continued environmental changes. Epigenetic modifications are necessary that control gene expression by changing chromatin status and recruiting various transcription regulators. The present study summarized the current knowledge on epigenetic modifications concerning plant responses to various environmental stressors. The functional relevance of epigenetic marks in regulating stress tolerance has been revealed, and epigenetic changes impact the effector genes. This study looks at the epigenetic mechanisms that govern plant abiotic stress responses, especially DNA methylation, histone methylation/acetylation, chromatin remodeling, and various metabolites. Plant breeders will benefit from a thorough understanding of these processes to create alternative crop improvement approaches. Genome editing with clustered regularly interspaced short palindromic repeat/CRISPR-associated proteins (CRISPR/Cas) provides genetic tools to make agricultural genetic engineering more sustainable and publicly acceptable.