Engineering abiotic stress tolerance via CRISPR/ Cas-mediated genome editing

Agrochemical-free genetically modified and genome-edited crops: Towards achieving the United Nations sustainable development goals and a 'greener' green revolution

Sustainable farming on ever-shrinking agricultural land and declining water resources for the growing human population is one of the greatest environmental and food security challenges of the 21st century. Conventional, age-old organic farming practices alone, and foods based on costly cellular agriculture, do not have the potential to be upscaled to meet the food supply challenges for feeding large populations. Additionally, agricultural practices relying on chemical inputs have a well-documented detrimental impact on human health and the environment. As the available farming methods have reached their productivity limits, new approaches to agriculture, combining friendly, age-old farming practices with modern technologies that exclude chemical interventions, are necessary to address the food production challenges. Growing genetically modified (GM) crops without chemical inputs can allow agricultural intensification with reduced adverse health and environmental impacts. Additionally, integrating high-value pleiotropic genes in their genetic improvement coupled with the use of modern agricultural technologies, like robotics and artificial intelligence (AI), will further improve productivity. Such 'organic-GM' crops will offer consumers healthy, agrochemical-free GM produce. We believe these agricultural practices will lead to the beginning of a potentially new chemical-free GM agricultural revolution in the era of Agriculture 4.0 and help meet the targets of the United Nations Sustainable Development Goals (SDGs). Furthermore, given the advancement in the genome editing (GE) toolbox, we ought to develop a new category of 'trait-reversible GM crops' to avert the fears of those who believe in ecological damage by GM crops. Thus, in this article, we advocate farming with no or minimal chemical use by combining chemical-free organic farming with the existing biofortified and multiple stress tolerant GM crops, while focusing on the development of novel 'biofertilizer-responsive GE crops' and 'trait-reversible GE crops' for the future.

Creating Climate-Resilient Crops by Increasing Drought, Heat, and Salt Tolerance

Over the years, the changes in the agriculture industry have been inevitable, considering the need to feed the growing population. As the world population continues to grow, food security has become challenged. Resources such as arable land and freshwater have become scarce due to quick urbanization in developing countries and anthropologic activities; expanding agricultural production areas is not an option. Environmental and climatic factors such as drought, heat, and salt stresses pose serious threats to food production worldwide. Therefore, the need to utilize the remaining arable land and water effectively and efficiently and to maximize the yield to support the increasing food demand has become crucial. It is essential to develop climate-resilient crops that will outperform traditional crops under any abiotic stress conditions such as heat, drought, and salt, as well as these stresses in any combinations. This review provides a glimpse of how plant breeding in agriculture has evolved to overcome the harsh environmental conditions and what the future would be like.

From genes to ecosystems: Decoding plant tolerance mechanisms to arsenic stress

Arsenic (As), a metalloid of considerable toxicity, has become increasingly bioavailable through anthropogenic activities, raising As contamination levels in groundwater and agricultural soils worldwide. This bioavailability has profound implications for plant biology and farming systems. As can detrimentally affect crop yield and pose risks of bioaccumulation and subsequent entry into the food chain. Upon exposure to As, plants initiate a multifaceted molecular response involving crucial signaling pathways, such as those mediated by calcium, mitogen-activated protein kinases, and various phytohormones (e.g., auxin, methyl jasmonate, cytokinin). These pathways, in turn, activate enzymes within the antioxidant system, which combat the reactive oxygen/nitrogen species (ROS and RNS) generated by As-induced stress. Plants exhibit a sophisticated genomic response to As, involving the upregulation of genes associated with uptake, chelation, and sequestration. Specific gene families, such as those coding for aquaglyceroporins and ABC transporters, are key in mediating As uptake and translocation within plant tissues. Moreover, we explore the gene regulatory networks that orchestrate the synthesis of phytochelatins and metallothioneins, which are crucial for As chelation and detoxification. Transcription factors, particularly those belonging to the MYB, NAC, and WRKY families, emerge as central regulators in activating As-responsive genes. On a post-translational level, we examine how ubiquitination pathways modulate the stability and function of proteins involved in As metabolism. By integrating omics findings, this review provides a comprehensive overview of the complex genomic landscape that defines plant responses to As. Knowledge gained from these genomic and epigenetic insights is pivotal for developing biotechnological strategies to enhance crop As tolerance.

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.

Early-responsive molecular signatures associated with halophytic adaptation in Sesuvium portulacastrum (L.)

Sesuvium portulacastrum (L.) is a halophyte, adapted to grow naturally under saline environments. The ability to use Na and K interchangeably indicated its facultative halophyte nature. No significant growth reduction occurs in seedlings up to 250 mM NaCl, except for curling of the youngest leaf. Within 8 h of salt treatment, seedlings accumulate proline, glycine betaine and other amino acids in both root and shoot. Despite a continued increase of tissue Na content, the number of differentially expressed genes (DEGs) decreases between 8 and 24 h of salt exposure, indicating transcriptional restoration after the initial osmotic challenge. At 8 h, upregulated genes mainly encode transporters and transcription factors, while genes in growth-related pathways such as photosynthesis and ribosome-associated biogenesis are suppressed. Overexpression of SpRAB18 (an ABA-responsive dehydrin), one of the most strongly induced DEGs, in soybean was found to increase biomass in control conditions and the growth benefit was maintained when plants were grown in 100 mM NaCl, indicating conservation of function in halophyte and glycophyte. An open-access transcriptome database "SesuviumKB" (https://cb.imsc.res.in/sesuviumkb/) was developed to involve the scientific community in wide-scale functional studies of S. portulacastrum genes, that could pave the way to engineer salt tolerance in crops.

Harnessing the potential of mutation breeding, CRISPR genome editing, and beyond for sustainable agriculture

By 2050, the global population is projected to exceed 9.5 billion, posing a formidable challenge to ensure food security worldwide. To address this pressing issue, mutation breeding in horticultural crops, utilizing physical or chemical methods, has emerged as a promising biotechnological strategy. However, the efficacy of these mutagens can be influenced by various factors, including biological and environmental variables, as well as targeted plant materials. This review highlights the global challenges related to food security and explores the potential of mutation breeding as an indispensable biotechnological tool in overcoming food insecurity. This review also covers the emergence of CRISPR-Cas9, a breakthrough technology offering precise genome editing for the development of high-yield, stress-tolerant crops. Together, mutation breeding and CRISPR can potentially address future food demands. This review focuses into these biotechnological advancements, emphasizing their combined potential to fortify global food security in the face of a booming population.

Depolymerized carrageenan expresses elicitor-like activity on Mentha arvensis L. under arsenic stress: Insights into arsenic resilience and monoterpene synthesis

Heavy metals contaminate agricultural land by limiting the productivity of crops and making them or their products unfit for consumption. Arsenic (As) is a potentially hazardous metalloid that severely impacts plants' survival. Menthol mint (Mentha arvensis L.) bears volatile compounds that are harshly exaggerated by diverse environmental factors like drought, salinity, heavy metal, temperature, photoperiod, and luminosity stresses. In this study, the phytotoxicity of As was examined in M. arvensis L. and its alleviation through the supplementation of oligomers of carrageenan. Noticeably, scanty information is available regarding the effect of irradiated carrageenan (ICA) on As-stressed plants. In order to observe the same in the case of M. arvensis L., the effect of ICA on As-treated plants was explored. The ICA concentration (foliar-applied) selected for the study was 80 mg L-1, 100 mg L-1 and 120 mg L-1, and that of As (soil-applied) was 80 mg kg-1 soil. Excess accumulation of As resulted in reduced growth, enzymatic activities, and yield and quality parameters of M. arvensis L. under As toxicity. However, the foliage application of ICA strengthens the antioxidant machinery and other physiological and oxidative stress biomarkers of the plant by facilitating the activity of superoxide dismutase (SOD), catalase (CAT), peroxidase (POX), and proline, and, therefore aids in alleviating the toxicity generated by As. Nevertheless, ICA supplementation proves beneficial in enhancing the monoterpene synthesis (essential oil production and its active constituents) of M. arvensis L. by maintaining a steady-state equilibrium between reactive oxygen species (ROS) production and its scavenging process.

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.

Toxic effects of lead on plants: integrating multi-omics with bioinformatics to develop Pb-tolerant crops

MAIN CONCLUSION

Lead disrupts plant metabolic homeostasis and key structural elements. Utilizing modern biotechnology tools, it's feasible to develop Pb-tolerant varieties by discovering biological players regulating plant metabolic pathways under stress. Lead (Pb) has been used for a variety of purposes since antiquity despite its toxic nature. After arsenic, lead is the most hazardous heavy metal without any known beneficial role in the biological system. It is a crucial inorganic pollutant that affects plant biochemical and morpho-physiological attributes. Lead toxicity harms plants throughout their life cycle and the extent of damage depends on the concentration and duration of exposure. Higher levels of lead exposure disrupt numerous key metabolic activities of plants including oxygen-evolving complex, organelles integrity, photosystem II connectivity, and electron transport chain. This review summarizes the detrimental effects of lead toxicity on seed germination, crop growth, and yield, oxidative and ultra-structural alterations, as well as nutrient absorption, transport, and assimilation. Further, it discusses the Pb-induced toxic modulation of stomatal conductance, photosynthesis, respiration, metabolic-enzymatic activity, osmolytes accumulation, and antioxidant activity. It is a comprehensive review that reports on omics-based studies along with morpho-physiological and biochemical modifications caused by lead stress. With advances in DNA sequencing technologies, genomics and transcriptomics are gradually becoming popular for studying Pb stress effects in plants. Proteomics and metabolomics are still underrated and there is a scarcity of published data, and this review highlights both their technical and research gaps. Besides, there is also a discussion on how the integration of omics with bioinformatics and the use of the latest biotechnological tools can aid in developing Pb-tolerant crops. The review concludes with core challenges and research directions that need to be addressed soon.

Molecular-Assisted Breeding of Cadmium Pollution-Safe Cultivars

Cadmium (Cd) contamination in edible agricultural products, especially in crops intended for consumption, has raised worldwide concerns regarding food safety. Breeding of Cd pollution-safe cultivars (Cd-PSCs) is an effective solution to preventing the entry of Cd into the food chain from contaminated agricultural soil. Molecular-assisted breeding methods, based on molecular mechanisms for cultivar-dependent Cd accumulation and bioinformatic tools, have been developed to accelerate and facilitate the breeding of Cd-PSCs. This review summarizes the recent progress in the research of the low Cd accumulation traits of Cd-PSCs in different crops. Furthermore, the application of molecular-assisted breeding methods, including transgenic approaches, genome editing, marker-assisted selection, whole genome-wide association analysis, and transcriptome, has been highlighted to outline the breeding of Cd-PSCs by identifying critical genes and molecular biomarkers. This review provides a comprehensive overview of the development of Cd-PSCs and the potential future for breeding Cd-PSC using modern molecular technologies.

Crop adaptation to climate change: An evolutionary perspective

The disciplines of evolutionary biology and plant and animal breeding have been intertwined throughout their development, with responses to artificial selection yielding insights into the action of natural selection and evolutionary biology providing statistical and conceptual guidance for modern breeding. Here we offer an evolutionary perspective on a grand challenge of the 21st century: feeding humanity in the face of climate change. We first highlight promising strategies currently under way to adapt crops to current and future climate change. These include methods to match crop varieties with current and predicted environments and to optimize breeding goals, management practices, and crop microbiomes to enhance yield and sustainable production. We also describe the promise of crop wild relatives and recent technological innovations such as speed breeding, genomic selection, and genome editing for improving environmental resilience of existing crop varieties or for developing new crops. Next, we discuss how methods and theory from evolutionary biology can enhance these existing strategies and suggest novel approaches. We focus initially on methods for reconstructing the evolutionary history of crops and their pests and symbionts, because such historical information provides an overall framework for crop-improvement efforts. We then describe how evolutionary approaches can be used to detect and mitigate the accumulation of deleterious mutations in crop genomes, identify alleles and mutations that underlie adaptation (and maladaptation) to agricultural environments, mitigate evolutionary trade-offs, and improve critical proteins. Continuing feedback between the evolution and crop biology communities will ensure optimal design of strategies for adapting crops to climate change.

CRISPR/Cas-mediated plant genome editing: outstanding challenges a decade after implementation

The discovery of the CRISPR/Cas genome-editing system has revolutionized our understanding of the plant genome. CRISPR/Cas has been used for over a decade to modify plant genomes for the study of specific genes and biosynthetic pathways as well as to speed up breeding in many plant species, including both model and non-model crops. Although the CRISPR/Cas system is very efficient for genome editing, many bottlenecks and challenges slow down further improvement and applications. In this review we discuss the challenges that can occur during tissue culture, transformation, regeneration, and mutant detection. We also review the opportunities provided by new CRISPR platforms and specific applications related to gene regulation, abiotic and biotic stress response improvement, and de novo domestication of plants.

Metabolic pathways engineering for drought or/and heat tolerance in cereals

Drought (D) and heat (H) are the two major abiotic stresses hindering cereal crop growth and productivity, either singly or in combination (D/+H), by imposing various negative impacts on plant physiological and biochemical processes. Consequently, this decreases overall cereal crop production and impacts global food availability and human nutrition. To achieve global food and nutrition security vis-a-vis global climate change, deployment of new strategies for enhancing crop D/+H stress tolerance and higher nutritive value in cereals is imperative. This depends on first gaining a mechanistic understanding of the mechanisms underlying D/+H stress response. Meanwhile, functional genomics has revealed several stress-related genes that have been successfully used in target-gene approach to generate stress-tolerant cultivars and sustain crop productivity over the past decades. However, the fast-changing climate, coupled with the complexity and multigenic nature of D/+H tolerance suggest that single-gene/trait targeting may not suffice in improving such traits. Hence, in this review-cum-perspective, we advance that targeted multiple-gene or metabolic pathway manipulation could represent the most effective approach for improving D/+H stress tolerance. First, we highlight the impact of D/+H stress on cereal crops, and the elaborate plant physiological and molecular responses. We then discuss how key primary metabolism- and secondary metabolism-related metabolic pathways, including carbon metabolism, starch metabolism, phenylpropanoid biosynthesis, γ-aminobutyric acid (GABA) biosynthesis, and phytohormone biosynthesis and signaling can be modified using modern molecular biotechnology approaches such as CRISPR-Cas9 system and synthetic biology (Synbio) to enhance D/+H tolerance in cereal crops. Understandably, several bottlenecks hinder metabolic pathway modification, including those related to feedback regulation, gene functional annotation, complex crosstalk between pathways, and metabolomics data and spatiotemporal gene expressions analyses. Nonetheless, recent advances in molecular biotechnology, genome-editing, single-cell metabolomics, and data annotation and analysis approaches, when integrated, offer unprecedented opportunities for pathway engineering for enhancing crop D/+H stress tolerance and improved yield. Especially, Synbio-based strategies will accelerate the development of climate resilient and nutrient-dense cereals, critical for achieving global food security and combating malnutrition.

CRISPR/Cas Technology Revolutionizes Crop Breeding

Crop breeding is an important global strategy to meet sustainable food demand. CRISPR/Cas is a most promising gene-editing technology for rapid and precise generation of novel germplasm and promoting the development of a series of new breeding techniques, which will certainly lead to the transformation of agricultural innovation. In this review, we summarize recent advances of CRISPR/Cas technology in gene function analyses and the generation of new germplasms with increased yield, improved product quality, and enhanced resistance to biotic and abiotic stress. We highlight their applications and breakthroughs in agriculture, including crop de novo domestication, decoupling the gene pleiotropy tradeoff, crop hybrid seed conventional production, hybrid rice asexual reproduction, and double haploid breeding; the continuous development and application of these technologies will undoubtedly usher in a new era for crop breeding. Moreover, the challenges and development of CRISPR/Cas technology in crops are also discussed.

Promoter editing for the genetic improvement of crops

Gene expression plays a fundamental role in the regulation of agronomically important traits in crop plants. The genetic manipulation of plant promoters through genome editing has emerged as an effective strategy to create favorable traits in crops by altering the expression pattern of the pertinent genes. Promoter editing can be applied in a directed manner, where nucleotide sequences associated with favorable traits are precisely generated. Alternatively, promoter editing can also be exploited as a random mutagenic approach to generate novel genetic variations within a designated promoter, from which elite alleles are selected based on their phenotypic effects. Pioneering studies have demonstrated the potential of promoter editing in engineering agronomically important traits as well as in mining novel promoter alleles valuable for plant breeding. In this review, we provide an update on the application of promoter editing in crops for increased yield, enhanced tolerance to biotic and abiotic stresses, and improved quality. We also discuss several remaining technical bottlenecks and how this strategy may be better employed for the genetic improvement of crops in the future.

LbCas12a mediated suppression of Cotton leaf curl Multan virus

Begomoviruses are contagious and severely affect commercially important fiber and food crops. Cotton leaf curl Multan virus (CLCuMuV) is one of the most dominant specie of Begomovirus and a major constraint on cotton yield in Pakistan. Currently, the field of plant genome editing is being revolutionized by the CRISPR/Cas system applications such as base editing, prime editing and CRISPR based gene drives. CRISPR/Cas9 system has successfully been used against biotic and abiotic plant stresses with proof-of-concept studies in both model and crop plants. CRISPR/Cas12 and CRISPR/Cas13 have recently been applied in plant sciences for basic and applied research. In this study, we used a novel approach, multiplexed crRNA-based Cas12a toolbox to target the different ORFs of the CLCuMuV genome at multiple sites simultaneously. This method successfully eliminated the symptoms of CLCuMuV in Nicotiana benthamiana and Nicotiana tabacum. Three individual crRNAs were designed from the CLCuMuV genome, targeting the specific sites of four different ORFs (C1, V1 and overlapping region of C2 and C3). The Cas12a-based construct Cas12a-MV was designed through Golden Gate three-way cloning for precise editing of CLCuMuV genome. Cas12a-MV construct was confirmed through whole genome sequencing using the primers Ubi-intron-F1 and M13-R1. Transient assays were performed in 4 weeks old Nicotiana benthamiana plants, through the agroinfiltration method. Sanger sequencing indicated that the Cas12a-MV constructs made a considerable mutations at the target sites of the viral genome. In addition, TIDE analysis of Sanger sequencing results showed the editing efficiency of crRNA1 (21.7%), crRNA2 (24.9%) and crRNA3 (55.6%). Furthermore, the Cas12a-MV construct was stably transformed into Nicotiana tabacum through the leaf disc method to evaluate the potential of transgenic plants against CLCuMuV. For transgene analysis, the DNA of transgenic plants of Nicotiana tabacum was subjected to PCR to amplify Cas12a genes with specific primers. Infectious clones were agro-inoculated in transgenic and non-transgenic plants (control) for the infectivity assay. The transgenic plants containing Cas12a-MV showed rare symptoms and remained healthy compared to control plants with severe symptoms. The transgenic plants containing Cas12a-MV showed a significant reduction in virus accumulation (0.05) as compared to control plants (1.0). The results demonstrated the potential use of the multiplex LbCas12a system to develop virus resistance in model and crop plants against begomoviruses.

Genetic resources and breeding approaches for improvement of amaranth (Amaranthus spp.) and quinoa (Chenopodium quinoa)

Nowadays, the human population is more concerned about their diet and very specific in choosing their food sources to ensure a healthy lifestyle and avoid diseases. So people are shifting to more smart nutritious food choices other than regular cereals and staple foods they have been eating for a long time. Pseudocereals, especially, amaranth and quinoa, are important alternatives to traditional cereals due to comparatively higher nutrition, essential minerals, amino acids, and zero gluten. Both Amaranchaceae crops are low-input demanding and hardy plants tolerant to stress, drought, and salinity conditions. Thus, these crops may benefit developing countries that follow subsistence agriculture and have limited farming resources. However, these are underutilized orphan crops, and the efforts to improve them by reducing their saponin content remain ignored for a long time. Furthermore, these crops have very rich variability, but the progress of their genetic gain for getting high-yielding genotypes is slow. Realizing problems in traditional cereals and opting for crop diversification to tackle climate change, research should be focused on the genetic improvement for low saponin, nutritionally rich, tolerant to biotic and abiotic stresses, location-specific photoperiod, and high yielding varietal development of amaranth and quinoa to expand their commercial cultivation. The latest technologies that can accelerate the breeding to improve yield and quality in these crops are much behind and slower than the already established major crops of the world. We could learn from past mistakes and utilize the latest trends such as CRISPR/Cas, TILLING, and RNA interference (RNAi) technology to improve these pseudocereals genetically. Hence, the study reviewed important nutrition quality traits, morphological descriptors, their breeding behavior, available genetic resources, and breeding approaches for these crops to shed light on future breeding strategies to develop superior genotypes.

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.

Targeted genome editing in polyploids: lessons from Brassica

CRISPR-mediated genome editing has emerged as a powerful tool for creating targeted mutations in the genome for various applications, including studying gene functions, engineering resilience against biotic and abiotic stresses, and increasing yield and quality. However, its utilization is limited to model crops for which well-annotated genome sequences are available. Many crops of dietary and economic importance, such as wheat, cotton, rapeseed-mustard, and potato, are polyploids with complex genomes. Therefore, progress in these crops has been hampered due to genome complexity. Excellent work has been conducted on some species of Brassica for its improvement through genome editing. Although excellent work has been conducted on some species of Brassica for genome improvement through editing, work on polyploid crops, including U's triangle species, holds numerous implications for improving other polyploid crops. In this review, we summarize key examples from genome editing work done on Brassica and discuss important considerations for deploying CRISPR-mediated genome editing more efficiently in other polyploid crops for improvement.

Plants' Response Mechanisms to Salinity Stress

Soil salinization is a severe abiotic stress that negatively affects plant growth and development, leading to physiological abnormalities and ultimately threatening global food security. The condition arises from excessive salt accumulation in the soil, primarily due to anthropogenic activities such as irrigation, improper land uses, and overfertilization. The presence of Na⁺, Cl^-, and other related ions in the soil above normal levels can disrupt plant cellular functions and lead to alterations in essential metabolic processes such as seed germination and photosynthesis, causing severe damage to plant tissues and even plant death in the worst circumstances. To counteract the effects of salt stress, plants have developed various mechanisms, including modulating ion homeostasis, ion compartmentalization and export, and the biosynthesis of osmoprotectants. Recent advances in genomic and proteomic technologies have enabled the identification of genes and proteins involved in plant salt-tolerance mechanisms. This review provides a short overview of the impact of salinity stress on plants and the underlying mechanisms of salt-stress tolerance, particularly the functions of salt-stress-responsive genes associated with these mechanisms. This review aims at summarizing recent advances in our understanding of salt-stress tolerance mechanisms, providing the key background knowledge for improving crops' salt tolerance, which could contribute to the yield and quality enhancement in major crops grown under saline conditions or in arid and semiarid regions of the world.

Twenty years of mining salt tolerance genes in soybean

Current combined challenges of rising food demand, climate change and farmland degradation exert enormous pressure on agricultural production. Worldwide soil salinization, in particular, necessitates the development of salt-tolerant crops. Soybean, being a globally important produce, has its genetic resources increasingly examined to facilitate crop improvement based on functional genomics. In response to the multifaceted physiological challenge that salt stress imposes, soybean has evolved an array of defences against salinity. These include maintaining cell homeostasis by ion transportation, osmoregulation, and restoring oxidative balance. Other adaptations include cell wall alterations, transcriptomic reprogramming, and efficient signal transduction for detecting and responding to salt stress. Here, we reviewed functionally verified genes that underly different salt tolerance mechanisms employed by soybean in the past two decades, and discussed the strategy in selecting salt tolerance genes for crop improvement. Future studies could adopt an integrated multi-omic approach in characterizing soybean salt tolerance adaptations and put our existing knowledge into practice via omic-assisted breeding and gene editing. This review serves as a guide and inspiration for crop developers in enhancing soybean tolerance against abiotic stresses, thereby fulfilling the role of science in solving real-life problems.

Supplementary Information

The online version contains supplementary material available at 10.1007/s11032-023-01383-3.

Editing efficiencies with Cas9 orthologs, Cas12a endonucleases, and temperature in rice

The advent of CRISPR-Cas technology has made it the genome editing tool of choice in all kingdoms of life, including plants, which can have large, highly duplicated genomes. As a result, finding adequate target sequences that meet the specificities of a given Cas nuclease on any gene of interest remains challenging in many cases. To assess target site flexibility, we tested five different Cas9/Cas12a endonucleases (SpCas9, SaCas9, St1Cas9, Mb3Cas12a, and AsCas12a) in embryogenic rice calli from Taipei 309 at 37°C (optimal temperature for most Cas9/Cas12a proteins) and 27°C (optimal temperature for tissue culture) and measured their editing rates under regular tissue culture conditions using Illumina sequencing. StCas9 and AsCas12 were not functional as tested, regardless of the temperature used. SpCas9 was the most efficient endonuclease at either temperature, regardless of whether monoallelic or biallelic edits were considered. Mb3Cas12a at 37°C was the next most efficient endonuclease. Monoallelic edits prevailed for both SaCas9 and Mb3Cas12a at 27°C, but biallelic edits prevailed at 37°C. Overall, the use of other Cas9 orthologs, the use of Cas12a endonucleases, and the optimal temperature can expand the range of targetable sequences.

Developing drought-smart, ready-to-grow future crops

Breeding crop plants with increased yield potential and improved tolerance to stressful environments is critical for global food security. Drought stress (DS) adversely affects agricultural productivity worldwide and is expected to rise in the coming years. Therefore, it is vital to understand the physiological, biochemical, molecular, and ecological mechanisms associated with DS. This review examines recent advances in plant responses to DS to expand our understanding of DS-associated mechanisms. Suboptimal water sources adversely affect crop growth and yields through physical impairments, physiological disturbances, biochemical modifications, and molecular adjustments. To control the devastating effect of DS in crop plants, it is important to understand its consequences, mechanisms, and the agronomic and genetic basis of DS for sustainable production. In addition to plant responses, we highlight several mitigation options such as omics approaches, transgenics breeding, genome editing, and biochemical to mechanical methods (foliar treatments, seed priming, and conventional agronomic practices). Further, we have also presented the scope of conventional and speed breeding platforms in helping to develop the drought-smart future crops. In short, we recommend incorporating several approaches, such as multi-omics, genome editing, speed breeding, and traditional mechanical strategies, to develop drought-smart cultivars to achieve the 'zero hunger' goal.

Abiotic stress tolerance in plants: a fascinating action of defense mechanisms

Climate fluctuation mediated abiotic stress consequences loss in crop yields. These stresses have a negative impact on plant growth and development by causing physiological and molecular changes. In this review, we have attempted to outline recent studies (5 years) associated with abiotic stress resistance in plants. We investigated the various factors that contribute to coping with abiotic challenges, such as transcription factors (TFs), microRNAs (miRNAs), epigenetic changes, chemical priming, transgenic breeding, autophagy, and non-coding RNAs. Stress responsive genes are regulated mostly by TFs, and these can be used to enhance stress resistance in plants. Plants express some miRNA during stress imposition that act on stress-related target genes to help them survive. Epigenetic alterations govern gene expression and facilitate stress tolerance. Chemical priming enhances growth in plants by modulating physiological parameters. Transgenic breeding enables identification of genes involved in precise plant responses during stressful situations. In addition to protein coding genes, non-coding RNAs also influence the growth of the plant by causing alterations at gene expression levels. For achieving sustainable agriculture for a rising world population, it is crucial to develop abiotic-resistant crops with anticipated agronomical traits. To achieve this objective, understanding the diverse mechanisms by which plants protect themselves against abiotic stresses is imperative. This review emphasizes on recent progress and future prospects for abiotic stress tolerance and productivity in plants.

Rice DST transcription factor negatively regulates heat tolerance through ROS-mediated stomatal movement and heat-responsive gene expression

Plants are frequently subjected to a broad spectrum of abiotic stresses including drought, salinity and extreme temperatures and have evolved both common and stress-specific responses to promote fitness and survival. Understanding the components and mechanisms that underlie both common and stress-specific responses can enable development of crop plants tolerant to different stresses. Here, we report a rice heat stress-tolerant 1 (hst1) mutant with increased heat tolerance. HST1 encodes the DST transcription factor, which also regulates drought and salinity tolerance. Increased heat tolerance of hst1 was associated with suppressed expression of reactive oxygen species (ROS)-scavenging peroxidases and increased ROS levels, which reduced water loss by decreasing stomatal aperture under heat stress. In addition, increased ROS levels enhanced expression of genes encoding heat shock protein (HSPs) including HSP80, HSP74, HSP58 and small HSPs. HSPs promote stabilization of proteins and protein refolding under heat stress and accordingly mutation of HST1 also improved reproductive traits including pollen viability and seed setting under high temperature. These results broaden the negative roles of DST in abiotic stress tolerance and provide important new insights into DST-regulated tolerance to diverse abiotic stresses through both shared and stress-specific mechanisms.

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.

Is CRISPR/Cas9 a way forward to fast-track genetic improvement in commercial palms? Prospects and limits

Commercially important palms (oil palm, coconut, and date palm) are widely grown perennial trees with tremendous commercial significance due to food, edible oil, and industrial applications. The mounting pressure on the human population further reinforces palms' importance, as they are essential crops to meet vegetable oil needs around the globe. Various conventional breeding methods are used for the genetic improvement of palms. However, adopting new technologies is crucial to accelerate breeding and satisfy the expanding population's demands. CRISPR/Cas9 is an efficient genome editing tool that can incorporate desired traits into the existing DNA of the plant without losing common traits. Recent progress in genome editing in oil palm, coconut and date palm are preliminarily introduced to potential readers. Furthermore, detailed information on available CRISPR-based genome editing and genetic transformation methods are summarized for researchers. We shed light on the possibilities of genome editing in palm crops, especially on the modification of fatty acid biosynthesis in oil palm. Moreover, the limitations in genome editing, including inadequate target gene screening due to genome complexities and low efficiency of genetic transformation, are also highlighted. The prospects of CRISPR/Cas9-based gene editing in commercial palms to improve sustainable production are also addressed in this review paper.

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.

CRISPR/Cas9 technology as an innovative approach to enhancing the phytoremediation: Concepts and implications

Phytoremediation is currently an active field of research focusing chiefly on identifying and characterizing novel and high chelation action super-accumulators. In the last few years, molecular tools have been widely exploited to understand better metal absorption, translocation, cation, and tolerance mechanisms in plants. Recently more advanced CRISPR-Cas9 genome engineering technology is also employed to enhance detoxification efficiency. Further, advances in molecular science will trigger the understanding of adaptive phytoremediation ability plant production in current global warming conditions. The enhanced abilities of nucleases for genome modification can improve plant repair capabilities by modifying the genome, thereby achieving a sustainable ecosystem. The purpose of this manuscript focuses on biotechnology's fundamental principles and application to promote climate-resistant metal plants, especially the CRISPR-Cas9 genome editing system for enhancing the phytoremediation of harmful contamination and pollutants.

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.

Developing Genetic Engineering Techniques for Control of Seed Size and Yield

Many signaling pathways regulate seed size through the development of endosperm and maternal tissues, which ultimately results in a range of variations in seed size or weight. Seed size can be determined through the development of zygotic tissues (endosperm and embryo) and maternal ovules. In addition, in some species such as rice, seed size is largely determined by husk growth. Transcription regulator factors are responsible for enhancing cell growth in the maternal ovule, resulting in seed growth. Phytohormones induce significant effects on entire features of growth and development of plants and also regulate seed size. Moreover, the vegetative parts are the major source of nutrients, including the majority of carbon and nitrogen-containing molecules for the reproductive part to control seed size. There is a need to increase the size of seeds without affecting the number of seeds in plants through conventional breeding programs to improve grain yield. In the past decades, many important genetic factors affecting seed size and yield have been identified and studied. These important factors constitute dynamic regulatory networks governing the seed size in response to environmental stimuli. In this review, we summarized recent advances regarding the molecular factors regulating seed size in Arabidopsis and other crops, followed by discussions on strategies to comprehend crops' genetic and molecular aspects in balancing seed size and yield.

An overview of salinity stress, mechanism of salinity tolerance and strategies for its management in cotton

Salinity stress is one of the primary threats to agricultural crops resulting in impaired crop growth and development. Although cotton is considered as reasonably salt tolerant, it is sensitive to salt stress at some critical stages like germination, flowering, boll formation, resulting in reduced biomass and fiber production. The mechanism of partial ion exclusion (exclusion of Na+ and/or Cl-) in cotton appears to be responsible for the pattern of uptake and accumulation of harmful ions (Na+ and Cl) in tissues of plants exposed to saline conditions. Maintaining high tissue K+/Na+ and Ca2+/Na+ ratios has been proposed as a key selection factor for salt tolerance in cotton. The key adaptation mechanism in cotton under salt stress is excessive sodium exclusion or compartmentation. Among the cultivated species of cotton, Egyptian cotton (Gossypium barbadense L.) exhibit better salt tolerance with good fiber quality traits as compared to most cultivated cotton and it can be used to improve five quality traits and transfer salt tolerance into Upland or American cotton (Gossypium hirsutum L.) by interspecific introgression. Cotton genetic studies on salt tolerance revealed that the majority of growth, yield, and fiber traits are genetically determined, and controlled by quantitative trait loci (QTLs). Molecular markers linked to genes or QTLs affecting key traits have been identified, and they could be utilized as an indirect selection criterion to enhance breeding efficiency through marker-assisted selection (MAS). Transfer of genes for compatible solute, which are an important aspect of ion compartmentation, into salt-sensitive species is, theoretically, a simple strategy to improve tolerance. The expression of particular stress-related genes is involved in plant adaptation to environmental stressors. As a result, enhancing tolerance to salt stress can be achieved by marker assisted selection added with modern gene editing tools can boost the breeding strategies that defend and uphold the structure and function of cellular components. The intent of this review was to recapitulate the advancements in salt screening methods, tolerant germplasm sources and their inheritance, biochemical, morpho-physiological, and molecular characteristics, transgenic approaches, and QTLs for salt tolerance in cotton.

Mutation of barley HvPDIL5-1 improves resistance to yellow mosaic virus disease without growth or yield penalties

The soil-borne yellow mosaic virus disease, which is caused by the bymoviruses barley yellow mosaic virus (BaYMV) and/or barley mild mosaic virus (BaMMV), seriously threatens winter barley production in Europe and East Asia. Both viruses are transmitted by the soil-borne plasmodiophorid Polymyxa graminis and are difficult to eliminate through chemical or physical measures in the field, making breeding for resistant cultivars the optimal strategy for disease control. The resistance locus rym1/11 was cloned encoding the host factor gene Protein Disulfide Isomerase Like 5-1 (PDIL5-1), whose loss-of-function variants confer broad-spectrum resistance to multiple strains of BaMMV/BaYMV. Most resistance-conferring variants have been identified in six-rowed barley landraces/historic cultivars, and their introgression into modern two-rowed malting cultivars is difficult because PDIL5-1 is located in a peri-centromeric region with suppressed recombination. In this study, we used CRISPR/Cas9 genome editing to modify PDIL5-1 in the BaYMV/BaMMV-susceptible elite malting barley cv. 'Golden Promise' and obtained the mutants pdil5-1-a and pdil5-1-b. PDIL5-1 in the pdil5-1-a mutant encodes a protein lacking a cysteine residue, and pdil5-1-b contains a protein-coding frameshift. Both mutants were completely resistant to BaYMV. The knockout mutant pdil5-1-b showed complete BaMMV resistance, while pdil5-1-a showed decreased viral accumulation but no disease symptoms if compared to 'Golden Promise'. Both PDIL5-1 edited lines, as well as the previously produced EMS-induced pdil5-1 mutant '10253-1-5' in the elite malting barley cv. 'Barke' background, displayed no growth or yield penalties in garden experiments or bymovirus-free field trials. Line '10253-1-5' showed improved resistance and yield performance compared to the wild-type and its sibling line when grown in infectious fields. Therefore, genome editing of the host factor gene PDIL5-1 could facilitate the breeding of barley varieties with resistance to bymoviruses.

Enabling Trade in Gene-Edited Produce in Asia and Australasia: The Developing Regulatory Landscape and Future Perspectives

Genome- or gene-editing (abbreviated here as ‘GEd’) presents great opportunities for crop improvement. This is especially so for the countries in the Asia-Pacific region, which is home to more than half of the world’s growing population. A brief description of the science of gene-editing is provided with examples of GEd products. For the benefits of GEd technologies to be realized, international policy and regulatory environments must be clarified, otherwise non-tariff trade barriers will result. The status of regulations that relate to GEd crop products in Asian countries and Australasia are described, together with relevant definitions and responsible regulatory bodies. The regulatory landscape is changing rapidly: in some countries, the regulations are clear, in others they are developing, and some countries have yet to develop appropriate policies. There is clearly a need for the harmonization or alignment of GEd regulations in the region: this will promote the path-to-market and enable the benefits of GEd technologies to reach the end-users.

State-of-the-art OMICS strategies against toxic effects of heavy metals in plants: A review

Environmental pollution of heavy metals (HMs), mainly due to anthropogenic activities, has received growing attention in recent decades. HMs, especially the non-essential carcinogenic ones, including chromium (Cr), cadmium (Cd), mercury (Hg), aluminum (Al), lead (Pb), and arsenic (As), have appeared as the most significant air, water, and soil pollutants, which adversely affect the quantity, quality, and security of plant-based food all over the world. Plants exposed to HMs could experience significant decline in growth and yield. To avoid or tolerate the toxic effects of HMs, plants have developed complicated defense mechanisms, including absorption and accumulation of HMs in cell organelles, immobilization by forming complexes with organic chelates, extraction by using numerous transporters, ion channels, signalling cascades, and transcription elements, among others. OMICS strategies have developed significantly to understand the mechanisms of plant transcriptomics, genomics, proteomics, metabolomics, and ionomics to counter HM-mediated stress stimuli. These strategies have been considered to be reliable and feasible for investigating the roles of genomics (genomes), transcriptomic (coding), mRNA transcripts (non-coding), metabolomics (metabolites), and ionomics (metal ions) to enhance stress resistance or tolerance in plants. The recent developments in the mechanistic understandings of the HMs-plant interaction in terms of their absorption, translocation, and toxicity invasions at the molecular and cellular levels, as well as plants' response and adaptation strategies against these stressors, are summarized in the present review. Transcriptomics, genomics, metabolomics, proteomics, and ionomics for plants against HMs toxicities are reviewed, while challenges and future recommendations are also discussed.

The Bibliometric Landscape of Gene Editing Innovation and Regulation in the Worldwide

Gene editing (GE) has become one of the mainstream bioengineering technologies over the past two decades, mainly fueled by the rapid development of the CRISPR/Cas system since 2012. To date, plenty of articles related to the progress and applications of GE have been published globally, but the objective, quantitative and comprehensive investigations of them are relatively few. Here, 13,980 research articles and reviews published since 1999 were collected by using GE-related queries in the Web of Science. We used bibliometric analysis to investigate the competitiveness and cooperation of leading countries, influential affiliations, and prolific authors. Text clustering methods were used to assess technical trends and research hotspots dynamically. The global application status and regulatory framework were also summarized. This analysis illustrates the bottleneck of the GE innovation and provides insights into the future trajectory of development and application of the technology in various fields, which will be helpful for the popularization of gene editing technology.

Comparative transcriptome analysis unveiling reactive oxygen species scavenging system of Sonneratia caseolaris under salinity stress

Many mangrove forests have undergone major changes as a result of human activity and global climate change. Sonneratia caseolaris is a common tree located in inner mangroves, and its range extends inland along tidal creeks, as far as the influence of salinity extends. This study investigated the physiological and molecular response mechanisms of S. caseolaris by analyzing its antioxidant defense capacity, including its differentially expressed genes (DEGs) under similar salt stress conditions. Salt treatment significantly affected the osmoprotectants and lipid peroxidation in S. caseolaris seedlings, which increased proline (Pro) content by 31.01-54.90% during all sample periods and decreased malonaldehyde (MDA) content by 12.81 and 18.17% at 25 and 40 days under 3.0% NaCl treatment. Antioxidant enzyme activities increased significantly following 3.0% NaCl treatment. Transcriptome analysis following De novo assembly showed 26,498 matched unigenes. The results showed that 1,263 DEGs responded to transcription factors (TFs) and plant phytohormones and mediated oxidoreductase activity to scavenge reactive oxygen species (ROS) in the control vs. 3.0% NaCl comparison. In addition, the transcription levels of genes associated with auxin and ethylene signal transduction also changed. Under salt stress, ROS scavenging genes (POD, CAT, and APX) and part of AP2, MYB, NAC, C2C2, bHLH, and WRKY TFs were upregulated. This study identified important pathways and candidate genes involved in S. caseolaris salinity tolerance and provided suggestions for further research into the mechanisms of salt tolerance in S. caseolaris.

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.

Reproductive-Stage Heat Stress in Cereals: Impact, Plant Responses and Strategies for Tolerance Improvement

Reproductive-stage heat stress (RSHS) poses a major constraint to cereal crop production by damaging main plant reproductive structures and hampering reproductive processes, including pollen and stigma viability, pollination, fertilization, grain setting and grain filling. Despite this well-recognized fact, research on crop heat stress (HS) is relatively recent compared to other abiotic stresses, such as drought and salinity, and in particular, RSHS studies in cereals are considerably few in comparison with seedling-stage and vegetative-stage-centered studies. Meanwhile, climate change-exacerbated HS, independently or synergistically with drought, will have huge implications on crop performance and future global food security. Fortunately, due to their sedentary nature, crop plants have evolved complex and diverse transient and long-term mechanisms to perceive, transduce, respond and adapt to HS at the molecular, cell, physiological and whole plant levels. Therefore, uncovering the molecular and physiological mechanisms governing plant response and tolerance to RSHS facilitates the designing of effective strategies to improve HS tolerance in cereal crops. In this review, we update our understanding of several aspects of RSHS in cereals, particularly impacts on physiological processes and yield; HS signal perception and transduction; and transcriptional regulation by heat shock factors and heat stress-responsive genes. We also discuss the epigenetic, post-translational modification and HS memory mechanisms modulating plant HS tolerance. Moreover, we offer a critical set of strategies (encompassing genomics and plant breeding, transgenesis, omics and agronomy) that could accelerate the development of RSHS-resilient cereal crop cultivars. We underline that a judicious combination of all of these strategies offers the best foot forward in RSHS tolerance improvement in cereals. Further, we highlight critical shortcomings to RSHS tolerance investigations in cereals and propositions for their circumvention, as well as some knowledge gaps, which should guide future research priorities. Overall, our review furthers our understanding of HS tolerance in plants and supports the rational designing of RSHS-tolerant cereal crop cultivars for the warming climate.

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.

Combined transcriptome and metabolome analysis of Nerium indicum L. elaborates the key pathways that are activated in response to witches' broom disease

BACKGROUND

Nerium indicum Mill. is an ornamental plant that is found in parks, riversides, lakesides, and scenic areas in China and other parts of the world. Our recent survey indicated the prevalence of witches' broom disease (WBD) in Guangdong, China. To find out the possible defense strategies against WBD, we performed a MiSeq based ITS sequencing to identify the possible casual organism, then did a de novo transcriptome sequencing and metabolome profiling in the phloem and stem tip of N. indicum plants suffering from WBD compared to healthy ones.

RESULTS

The survey showed that Wengyuen county and Zengcheng district had the highest disease incidence rates. The most prevalent microbial species in the diseased tissues was Cophinforma mamane. The transcriptome sequencing resulted in the identification of 191,224 unigenes of which 142,396 could be annotated. There were 19,031 and 13,284 differentially expressed genes (DEGs) between diseased phloem (NOWP) and healthy phloem (NOHP), and diseased stem (NOWS) and healthy stem (NOHS), respectively. The DEGs were enriched in MAPK-signaling (plant), plant-pathogen interaction, plant-hormone signal transduction, phenylpropanoid and flavonoid biosynthesis, linoleic acid and α-linoleic acid metabolism pathways. Particularly, we found that N. indicum plants activated the phytohormone signaling, MAPK-signaling cascade, defense related proteins, and the biosynthesis of phenylpropanoids and flavonoids as defense responses to the pathogenic infection. The metabolome profiling identified 586 metabolites of which 386 and 324 metabolites were differentially accumulated in NOHP vs NOWP and NOHS and NOWS, respectively. The differential accumulation of metabolites related to phytohormone signaling, linoleic acid metabolism, phenylpropanoid and flavonoid biosynthesis, nicotinate and nicotinamide metabolism, and citrate cycle was observed, indicating the role of these pathways in defense responses against the pathogenic infection.

CONCLUSION

Our results showed that Guangdong province has a high incidence of WBD in most of the surveyed areas. C. mamane is suspected to be the causing pathogen of WBD in N. indicum. N. indicum initiated the MAPK-signaling cascade and phytohormone signaling, leading to the activation of pathogen-associated molecular patterns and hypersensitive response. Furthermore, N. indicum accumulated high concentrations of phenolic acids, coumarins and lignans, and flavonoids under WBD. These results provide scientific tools for the formulation of control strategies of WBD in N. indicum.

GsERF1 enhances Arabidopsis thaliana aluminum tolerance through an ethylene-mediated pathway

Ethylene response factor (ERF) transcription factors constitute a subfamily of the AP2/ERF superfamily in plants and play multiple roles in plant growth and development as well as in stress responses. In this study, the GsERF1 gene from the wild soybean BW69 line (an Al-resistant Glycine soja line) was rapidly induced in response to aluminum stress. Quantitative real-time PCR (qRT-PCR) analysis showed that the GsERF1 gene maintained a constitutive expression pattern and was induced in soybean in response to aluminum stress, with increased amounts of transcripts detected in the roots. The putative GsERF1 protein, which contains an AP2 domain, was located in the nucleus and maintained transactivation activity. In addition, under AlCl3 treatment, GsERF1 overexpression increased the relative growth rate of the roots of Arabidopsis and weakened the hematoxylin staining of hairy roots. Ethylene synthesis-related genes such as ACS4, ACS5 and ACS6 were upregulated in GsERF1 transgenic lines compared with the wild type under AlCl3 treatment. Furthermore, the expression levels of stress/ABA-responsive marker genes, including ABI1, ABI2, ABI4, ABI5 and RD29B, in the GsERF1 transgenic lines were affected by AlCl3 treatment, unlike those in the wild type. Taken together, the results indicated that overexpression of GsERF1 may enhance aluminum tolerance of Arabidopsis through an ethylene-mediated pathway and/or ABA signaling pathway, the findings of which lay a foundation for breeding soybean plants tolerant to aluminum stress.

Increase Crop Resilience to Heat Stress Using Omic Strategies

Varieties of various crops with high resilience are urgently needed to feed the increased population in climate change conditions. Human activities and climate change have led to frequent and strong weather fluctuation, which cause various abiotic stresses to crops. The understanding of crops' responses to abiotic stresses in different aspects including genes, RNAs, proteins, metabolites, and phenotypes can facilitate crop breeding. Using multi-omics methods, mainly genomics, transcriptomics, proteomics, metabolomics, and phenomics, to study crops' responses to abiotic stresses will generate a better, deeper, and more comprehensive understanding. More importantly, multi-omics can provide multiple layers of information on biological data to understand plant biology, which will open windows for new opportunities to improve crop resilience and tolerance. However, the opportunities and challenges coexist. Interpretation of the multidimensional data from multi-omics and translation of the data into biological meaningful context remained a challenge. More reasonable experimental designs starting from sowing seed, cultivating the plant, and collecting and extracting samples were necessary for a multi-omics study as the first step. The normalization, transformation, and scaling of single-omics data should consider the integration of multi-omics. This review reports the current study of crops at abiotic stresses in particular heat stress using omics, which will help to accelerate crop improvement to better tolerate and adapt to climate change.

Impact of Pre-Anthesis Drought Stress on Physiology, Yield-Related Traits, and Drought-Responsive Genes in Green Super Rice

Optimum soil water availability is vital for maximum yield production in rice which is challenged by increasing spells of drought. The reproductive stage drought is among the main limiting factors leading to the drastic reduction in grain yield. The objective of this study was to investigate the molecular and morphophysiological responses of pre-anthesis stage drought stress in green super rice. The study assessed the performance of 26 rice lines under irrigated and drought conditions. Irrigated treatment was allowed to grow normally, while drought stress was imposed for 30 days at the pre-anthesis stage. Three important physiological traits including pollen fertility percentage (PFP), cell membrane stability (CMS), and normalized difference vegetative index (NDVI) were recorded at anthesis stage during the last week of drought stress. Agronomic traits of economic importance including grain yield were recorded at maturity stage. The analysis of variance demonstrated significant variation among the genotypes for most of the studied traits. Correlation and principal component analyses demonstrated highly significant associations of particular agronomic traits with grain yield, and genetic diversity among genotypes, respectively. Our study demonstrated a higher drought tolerance potential of GSR lines compared with local cultivars, mainly by higher pollen viability, plant biomass, CMS, and harvest index under drought. In addition, the molecular basis of drought tolerance in GSR lines was related to upregulation of certain drought-responsive genes including OsSADRI, OsDSM1, OsDT11, but not the DREB genes. Our study identified novel drought-responsive genes (LOC_Os11g36190, LOC_Os12g04500, LOC_Os12g26290, and LOC_Os02g11960) that could be further characterized using reverse genetics to be utilized in molecular breeding for drought tolerance.

Expression profiling of TaARGOS homoeologous drought responsive genes in bread wheat

Drought tolerant germplasm is needed to increase crop production, since water scarcity is a critical bottleneck in crop productivity worldwide. Auxin Regulated Gene involved in Organ Size (ARGOS) is a large protein family of transcription factors that plays a vital role in organ size, plant growth, development, and abiotic stress responses in plants. Although, the ARGOS gene family has been discovered and functionalized in a variety of crop plants, but a comprehensive and systematic investigation of ARGOS genes in locally used commercial wheat cultivars is still yet to be reported. The relative expression of three highly conserved TaARGOS homoeologous genes (TaARGOS-A, TaARGOS-B, TaARGOS-D) was studied in three drought-tolerant (Pakistan-2013, NARC-2009 and NR-499) and three sensitive (Borlaug-2016, NR-514 and NR-516) wheat genotypes under osmotic stress, induced by PEG-6000 at 0 (exogenous control), 2, 4, 6, and 12 h. The normalization of target genes was done using β-actin as endogenous control, whereas DREB3, as a marker gene was also transcribed, reinforcing the prevalence of dehydration in all stress treatments. Real-time quantitative PCR revealed that osmotic stress induced expression of the three TaARGOS transcripts in different wheat seedlings at distinct timepoints. Overall, all genes exhibited significantly higher expression in the drought-tolerant genotypes as compared to the sensitive ones. For instance, the expression profile of TaARGOS-A and TaARGOS-D showed more than threefold increase at 2 h and six to sevenfold increase after 4 h of osmotic stress. However, after 6 h of osmotic stress these genes started to downregulate, and the lowest gene expression was noticed after 12 h of osmotic stress. Among all the homoeologous genes, TaARGOS-D, in particular, had a more significant influence on controlling plant growth and drought tolerance as it showed the highest expression. Altogether, TaARGOSs are involved in seedling establishment and overall plant growth. In addition, the tolerant group of genotypes had a much greater relative fold expression than the sensitive genotypes. Ultimately, Pakistan-2013 showed the highest relative expression of the studied genes than other genotypes which shows its proficiency to mitigate osmotic stress. Therefore, it could be cultivated in arid and semi-arid regions under moisture-deficient regimes. These findings advocated the molecular mechanism and regulatory roles of TaARGOS genes in plant growth and osmotic stress tolerance in contrasting groups of wheat genotypes, accompanied by the genetic nature of identified genotypes in terms of their potential for drought tolerance.