Engineering plant virus resistance: from RNA silencing to genome editing strategies

CRISPR/Cas: An Emerging Toolbox for Engineering Virus Resistance in Plants

Clustered regularly interspaced short palindromic repeats (CRISPR)/Cas have been recognized as powerful genome-editing tools in diverse eukaryotic species, including plants, and thus hold great promise for engineering virus resistance in plants. Nevertheless, further attention is required regarding various issues associated with applying new powerful technologies in the field. This mini-review focuses on the recent advances in using CRISPR/Cas9 and CRISPR/Cas13 systems to combat DNA and RNA viruses in plants. We explored the utility of CRISPR/Cas for targeting the viral genome and editing host susceptibility genes in plants. We also provide insights into the limitations and challenges of using CRISPR/Cas for plant virus interference and propose individual combinatorial solutions. In conclusion, CRISPR/Cas technology has the potential to offer innovative and highly efficient approaches for controlling viruses in important crops in the near future.

An asymptomatic geminivirus activates autophagy and enhances plant defenses against diverse pathogens

Plant viral diseases cause great losses in agricultural production. Virus cross-protection is a strategy in which a mild virus is employed to shield plants against subsequent infections by severe viral strains. However, this approach is restricted to protection against the same viruses. In this study, we observed that pre-inoculation with apple geminivirus (AGV) reduced the accumulation of secondarily infected heterologous viruses, such as cucumber mosaic virus, potato virus X, and tobacco mosaic virus in Nicotiana benthamiana, tomato, and pepper plants. Transcriptional expression analysis showed that autophagy-related genes were transcriptionally up-regulated upon AGV inoculation at an early stage of infection. Accordingly, autophagic activity was observed to be elevated following AGV infection. Interestingly, AGV accumulation was reduced in autophagy-deficient plants, suggesting that autophagy activation promotes AGV infection in the plant. Moreover, pre-inoculation with AGV provided cross-protection against infection with a phytopathogenic bacterium (Pseudomonas syringae) and fungus (Botrytis cinerea) in Nicotiana species. In summary, our study showed that AGV, an asymptomatic virus, could protect plants against severe viral, fungal, and bacterial diseases to some extent through the activation of autophagy pathways, highlighting its potential as a biocontrol agent for managing a wide range of plant crop diseases in the field.

Plant Immunity against Tobamoviruses

Tobamoviruses are a group of plant viruses that pose a significant threat to agricultural crops worldwide. In this review, we focus on plant immunity against tobamoviruses, including pattern-triggered immunity (PTI), effector-triggered immunity (ETI), the RNA-targeting pathway, phytohormones, reactive oxygen species (ROS), and autophagy. Further, we highlight the genetic resources for resistance against tobamoviruses in plant breeding and discuss future directions on plant protection against tobamoviruses.

Unraveling plant-microbe interactions: can integrated omics approaches offer concrete answers?

Advances in high throughput omics techniques provide avenues to decipher plant microbiomes. However, there is limited information on how integrated informatics can help provide deeper insights into plant-microbe interactions in a concerted way. Integrating multi-omics datasets can transform our understanding of the plant microbiome from unspecified genetic influences on interacting species to specific gene-by-gene interactions. Here, we highlight recent progress and emerging strategies in crop microbiome omics research and review key aspects of how the integration of host and microbial omics-based datasets can be used to provide a comprehensive outline of complex crop-microbe interactions. We describe how these technological advances have helped unravel crucial plant and microbial genes and pathways that control beneficial, pathogenic, and commensal plant-microbe interactions. We identify crucial knowledge gaps and synthesize current limitations in our understanding of crop microbiome omics approaches. We highlight recent studies in which multi-omics-based approaches have led to improved models of crop microbial community structure and function. Finally, we recommend holistic approaches in integrating host and microbial omics datasets to achieve precision and efficiency in data analysis, which is crucial for biotic and abiotic stress control and in understanding the contribution of the microbiota in shaping plant fitness.

Australian Cool-Season Pulse Seed-Borne Virus Research: 1. Alfalfa and Cucumber Mosaic Viruses and Less Important Viruses

Here, we review the research undertaken since the 1950s in Australia's grain cropping regions on seed-borne virus diseases of cool-season pulses caused by alfalfa mosaic virus (AMV) and cucumber mosaic virus (CMV). We present brief background information about the continent's pulse industry, virus epidemiology, management principles and future threats to virus disease management. We then take a historical approach towards all past investigations with these two seed-borne pulse viruses in the principal cool-season pulse crops grown: chickpea, faba bean, field pea, lentil, narrow-leafed lupin and white lupin. With each pathosystem, the main focus is on its biology, epidemiology and management, placing particular emphasis on describing field and glasshouse experimentation that enabled the development of effective phytosanitary, cultural and host resistance control strategies. Past Australian cool-season pulse investigations with AMV and CMV in the less commonly grown species (vetches, narbon bean, fenugreek, yellow and pearl lupin, grass pea and other Lathyrus species) and those with the five less important seed-borne pulse viruses also present (broad bean stain virus, broad bean true mosaic virus, broad bean wilt virus, cowpea mild mottle virus and peanut mottle virus) are also summarized. The need for future research is emphasized, and recommendations are made regarding what is required.

Host Resistance to Virus Diseases Provides a Key Enabler towards Fast Tracking Gains in Grain Lupin Breeding

Four lupin species, Lupinus angustifolius, L. albus, L. luteus, and L. mutabilis, are grown as cool-season grain legume crops. Fifteen viruses infect them. Two of these, bean yellow mosaic virus (BYMV) and cucumber mosaic virus (CMV), cause diseases that threaten grain lupin production. Phytosanitary and cultural control measures are mainly used to manage them. However, breeding virus-resistant lupin cultivars provides an additional management approach. The need to develop this approach stimulated a search for virus resistance sources amongst cultivated lupin species and their wild relatives. This review focuses on the progress made in optimizing virus resistance screening procedures, identifying host resistances to BYMV, CMV, and additional viral pathogen alfalfa mosaic virus (AMV), and the inclusion of BYMV and CMV resistance within lupin breeding programs. The resistance types found in different combinations of virus and grain lupin species include localized hypersensitivity, systemic hypersensitivity, extreme resistance, and partial resistance to aphid or seed transmission. These resistances provide a key enabler towards fast tracking gains in grain lupin breeding. Where studied, their inheritance depended upon single dominant genes or was polygenic. Although transgenic virus resistance was incorporated into L. angustifolius and L. luteus successfully, it proved unstable. Priorities for future research are discussed.

Plant protection from virus: a review of different approaches

This review analyzes methods for controlling plant viral infection. The high harmfulness of viral diseases and the peculiarities of viral pathogenesis impose special requirements regarding developing methods to prevent phytoviruses. The control of viral infection is complicated by the rapid evolution, variability of viruses, and the peculiarities of their pathogenesis. Viral infection in plants is a complex interdependent process. The creation of transgenic varieties has caused much hope in the fight against viral pathogens. The disadvantages of genetically engineered approaches include the fact that the resistance gained is often highly specific and short-lived, and there are bans in many countries on the use of transgenic varieties. Modern prevention methods, diagnosis, and recovery of planting material are at the forefront of the fight against viral infection. The main techniques used for the healing of virus-infected plants include the apical meristem method, which is combined with thermotherapy and chemotherapy. These methods represent a single biotechnological complex method of plant recovery from viruses in vitro culture. It widely uses this method for obtaining non-virus planting material for various crops. The disadvantages of the tissue culture-based method of health improvement include the possibility of self-clonal variations resulting from the long-term cultivation of plants under in vitro conditions. The possibilities of increasing plant resistance by stimulating their immune system have expanded, which results from the in-depth study of the molecular and genetic bases of plant resistance toward viruses and the investigation of the mechanisms of induction of protective reactions in the plant organism. The existing methods of phytovirus control are ambiguous and require additional research. Further study of the genetic, biochemical, and physiological features of viral pathogenesis and the development of a strategy to increase plant resistance to viruses will allow a new level of phytovirus infection control to be reached.

Editing of TOM1 gene in tobacco using CRISPR/Cas9 confers resistance to Tobacco mosaic virus

BACKGROUND

Genome editing technology has become one of the excellent tools for precise plant breeding to develop novel plant germplasm. The Tobacco mosaic virus (TMV) is the most prominent pathogen that infects several Solanaceae plants, such as tobacco, tomato, and capsicum, which requires critical host factors for infection and replication of its genomic RNA in the host. The Tobamovirus multiplication (TOM) genes, such as TOM1, TOM2A, TOM2B, and TOM3, are involved in the multiplication of Tobamoviruses. TOM1 is a transmembrane protein necessary for efficient TMV multiplication in several plant species. The TOM genes are crucial recessive resistance genes that act against the tobamoviruses in various plant species.

METHODS AND RESULTS

The single guided RNA (sgRNA) was designed to target the first exon of the NtTOM1 gene and cloned into the pHSE401 vector. The pHSE401-NtTOM1 vector was introduced into Agrobacterium tumefaciens strain LBA4404 and then transformed into tobacco plants. The analysis on T0 transgenic plants showed the presence of the hptII and Cas9 transgenes. The sequence analysis of the NtTOM1 from T0 plants showed the indels. Genotypic evaluation of the NtTOM1 mutant lines displayed the stable inheritance of the mutations in the subsequent generations of tobacco plants. The NtTOM1 mutant lines successfully conferred resistance to TMV.

CONCLUSIONS

CRISPR/Cas genome editing is a reliable tool for investigating gene function and precision breeding across different plant species, especially the species in the Solanaceae family.

CRISPR-Cas engineering in food science and sustainable agriculture: recent advancements and applications

The developments in the food supply chain to support the growing population of the world is one of today's most pressing issues, and to achieve this goal improvements should be performed in both crops and microbes. For this purpose, novel approaches such as genome editing (GE) methods have upgraded the biological sciences for genome manipulation and, among such methods, clustered regularly interspaced short palindromic repeats (CRISPR) and CRISPR-associated proteins (Cas) are the main exciting innovations since the Green Revolution. CRISPR/Cas systems can be a potent tool for the food industry, improvement of agricultural crops and even for protecting food-grade bacteria from foreign genetic invasive elements. This review introduces the history and mechanism of the CRISPR-Cas system as a genome editing tool and its applications in the vaccination of starter cultures, production of antimicrobials and bioactive compounds, and genome editing of microorganisms.

Priming crop plants with rosemary (Salvia rosmarinus Spenn, syn Rosmarinus officinalis L.) extract triggers protective defense response against pathogens

Plant bioactive compounds provide novel straightforward approaches to control plant diseases. Rosemary (Salvia rosmarinus)-derived extracts carry many prominent pharmacological activities, including antimicrobial and antioxidant, mainly due to its phenolic compounds, rosmarinic acid (RA), carnosic acid and carnosol. However, the effects of these extracts on plant diseases are still unknown, which constrains its potential application as bioprotectant in the agricultural production. In this study we demonstrate the antiviral effect of the aqueous rosemary extract (ARE) against tobacco necrosis virus strain A (TNVA) in ARE-treated tobacco (Nicotiana tabacum) plants. Our results show that ARE-treatment enhances plant defense response, contributing to reduce virus replication and systemic movement in tobacco plants. RA, the main phenolic compound detected in this extract, is one of the main inducers of TNVA control. The ARE-induced protection in TNVA-infected plants was characterized by the expression of H₂O₂ scavengers and defense-related genes, involving salicylic acid- and jasmonic acid-regulated pathways. Furthermore, treatment with ARE in lemon (Citrus limon) and soybean (Glycine max) leaves protects the plants against Xanthomonas citri subsp. citri and Diaporthe phaseolorum var. meridionalis, respectively. Additionally, ARE treatment also promotes growth and development, suggesting a biostimulant activity in soybean. These results open the way for the potential use of ARE as a bioprotective agent in disease management.

Cauliflower mosaic virus: Virus-host interactions and its uses in biotechnology and medicine

Cauliflower mosaic virus (CaMV) was the first discovered plant virus with genomic DNA that uses reverse transcriptase for replication. The CaMV 35S promoter is a constitutive promoter and thus, an attractive driver of gene expression in plant biotechnology. It is used in most transgenic crops to activate foreign genes which have been artificially inserted into the host plant. In the last century, producing food for the world's population while preserving the environment and human health is the main topic of agriculture. The damage caused by viral diseases has a significant negative economic impact on agriculture, and disease control is based on two strategies: immunization and prevention to contain virus spread, so correct identification of plant viruses is important for disease management. Here, we discuss CaMV from different aspects: taxonomy, structure and genome, host plants and symptoms, transmission and pathogenicity, prevention, control and application in biotechnology as well as in medicine. Also, we calculated the CAI index for three ORFs IV, V, and VI of the CaMV virus in host plants, the results of which can be used in the discussion of gene transfer or antibody production to identify the CaMV.

Plant translational reprogramming for stress resilience

Organisms regulate gene expression to produce essential proteins for numerous biological processes, from growth and development to stress responses. Transcription and translation are the major processes of gene expression. Plants evolved various transcription factors and transcriptome reprogramming mechanisms to dramatically modulate transcription in response to environmental cues. However, even the genome-wide modulation of a gene's transcripts will not have a meaningful effect if the transcripts are not properly biosynthesized into proteins. Therefore, protein translation must also be carefully controlled. Biotic and abiotic stresses threaten global crop production, and these stresses are seriously deteriorating due to climate change. Several studies have demonstrated improved plant resistance to various stresses through modulation of protein translation regulation, which requires a deep understanding of translational control in response to environmental stresses. Here, we highlight the translation mechanisms modulated by biotic, hypoxia, heat, and drought stresses, which are becoming more serious due to climate change. This review provides a strategy to improve stress tolerance in crops by modulating translational regulation.

CRISPR/Cas9-mediated gene editing of vacuolar ATPase subunit d mediates phytohormone biosynthesis and virus resistance in rice

Vacuolar ATPases (V-ATPases) are proton pumps for proton translocation across membranes that utilize energy derived from ATP hydrolysis; OsV-ATPase subunit d (OsV-ATPase d) is part of an integral, membrane-embedded V0 complex in the V-ATPase complex. Whether OsV-ATPase d is involved in phytohormone biosynthesis and resistance in rice remains unknown. The knockout mutants of OsV-ATPase d in rice were generated using the CRISPR/Cas9 system, and mutation of OsV-ATPase d did not show any detrimental effect on plant growth or yield productivity. Transcriptomic results showed that OsV-ATPase d is probably involved in mediating the biosynthesis of plant hormones and resistance in rice. Compared to wild type, mutation of OsV-ATPase d significantly increased JA and ABA biosynthesis and resistance against Southern rice black-streaked dwarf virus (SRBSDV), but it decreased resistance against Rice stripe virus (RSV) in rice. The data presented in this study reveal that OsV-ATPase d mediates phytohormone biosynthesis and virus resistance in rice and can be selected as a potential target for resistance breeding in rice.

On-site and visual detection of sorghum mosaic virus and rice stripe mosaic virus based on reverse transcription-recombinase-aided amplification and CRISPR/Cas12a

Rapid, sensitive and visual detection of plant viruses is conducive to effective prevention and control of plant viral diseases. Therefore, combined with reverse transcription and recombinase-aided amplification, we developed a CRISPR/Cas12a-based visual nucleic acid detection system targeting sorghum mosaic virus and rice stripe mosaic virus, which cause harm to crop production in field. When the RT-RAA products were recognized by crRNA and formed a complex with LbCas12a, the ssDNA labeled with a quenched green fluorescent molecule will be cleaved by LbCas12a, and then a significant green fluorescence signal will appear. The entire detection process can be completed within 30 min without using any sophisticated equipment and instruments. The detection system could detect samples at a dilution of 10⁷, about 10⁴-fold improvement over RT-PCR, so the system was successfully to detect rice stripe mosaic virus in a single leafhopper, which is the transmission vector of the virus. Finally, the CRISPR/Cas12a-based detection system was utilized to on-site detect the two viruses in the field, and the results were fully consistent with that we obtained by RT-PCR in laboratory, demonstrating that it has the application prospect of detecting important crop viruses in the field.

Multiple integrations of a sense transgene, including a tandem inverted repeat confer stable RNA-silencing mediated virus resistance under different abiotic and biotic conditions

In a previous study, tobacco plants, transformed with a sense construct of the 57K domain of the replicase gene of tobacco rattle virus (TRV), provided resistance against genetically distant isolates of the virus. In this work, 57K-specific siRNAs were detected with RT-qPCR solely in the resistant line verifying the RNA-silencing base of the resistance. The integration sites of the transgene into the plant genome were identified with inverse-PCR. Moreover, the resistance against TRV was practically unaffected by low temperature conditions and the presence of heterologous viruses. The mechanism of the resistance was further examined by a gene expression analysis that showed increased transcript levels of genes with a key-role in the RNA silencing pathway and the basal antiviral defence. This work provides a comprehensive characterization of the robust virus resistance obtained by a sense transgene and underlines the usefulness of transgenic plants obtained by such a strategy.

CRISPR/Cas technology: Opportunities for phytopathogenic viruses detection

Detection and monitoring of viruses are essential for healthy plants and prosperity. Recent development in CRISPR/Cas system in diagnosis has open an avenue well suited for pathogen detection. Variety of CRISPR associated proteins are being discovered, suggesting array of application and detection strategies in diagnosis. Phytopathogenic viruses are diverse with respect to their nucleic acid compositions, which presents a challenge in developing a single device applicable for almost all viruses. The review describes about the efficient use of CRISPR/Cas Technology in diagnosis, such as SHERLOCK, DETECTR and SATORI. These methods are different in their characteristic to identify specific nucleic acids and processing the detectable signals. These technologies are in their infancy and lot of scope is there to develop commercial kits. Plant tissue culture-based industries, climate control green houses, indoor cultivation facilities etc. has been considered as few examples. This review will be beneficial for researchers seeking to develop detection mechanism based on CRISPR/Cas technology. The outcome in the form of cost-effective detection of viruses will be boon for agro-based industries, which are facing challenges through virus contamination.

CRISPR/Cas-based tools for the targeted control of plant viruses

Plant viruses are known to infect most economically important crops and pose a major threat to global food security. Currently, few resistant host phenotypes have been delineated, and while chemicals are used for crop protection against insect pests and bacterial or fungal diseases, these are inefficient against viral diseases. Genetic engineering emerged as a way of modifying the plant genome by introducing functional genes in plants to improve crop productivity under adverse environmental conditions. Recently, new breeding technologies, and in particular the exciting CRISPR/Cas (clustered regularly interspaced short palindromic repeats/CRISPR-associated proteins) technology, was shown to be a powerful alternative to engineer resistance against plant viruses, thus has great potential for reducing crop losses and improving plant productivity to directly contribute to food security. Indeed, it could circumvent the "Genetic modification" issues because it allows for genome editing without the integration of foreign DNA or RNA into the genome of the host plant, and it is simpler and more versatile than other new breeding technologies. In this review, we describe the predominant features of the major CRISPR/Cas systems and outline strategies for the delivery of CRISPR/Cas reagents to plant cells. We also provide an overview of recent advances that have engineered CRISPR/Cas-based resistance against DNA and RNA viruses in plants through the targeted manipulation of either the viral genome or susceptibility factors of the host plant genome. Finally, we provide insight into the limitations and challenges that CRISPR/Cas technology currently faces and discuss a few alternative applications of the technology in virus research.

Targeting of genomic and negative-sense strands of viral RNA contributes to antiviral resistance mediated by artificial miRNAs and promotes the emergence of complex viral populations

Technology based on artificial small RNAs, including artificial microRNAs (amiRNAs), exploits natural RNA silencing mechanisms to achieve silencing of endogenous genes or pathogens. This technology has been successfully employed to generate resistance against different eukaryotic viruses. However, information about viral RNA molecules effectively targeted by these small RNAs is rather conflicting, and factors contributing to the selection of virus mutants escaping the antiviral activity of virus-specific small RNAs have not been studied in detail. In this work, we transformed Nicotiana benthamiana plants with amiRNA constructs designed against the potyvirus plum pox virus (PPV), a positive-sense RNA virus, and obtained lines highly resistant to PPV infection and others showing partial resistance. These lines have allowed us to verify that amiRNA directed against genomic RNA is more efficient than amiRNA targeting its complementary strand. However, we also provide evidence that the negative-sense RNA strand is cleaved by the amiRNA-guided RNA silencing machinery. Our results show that the selection pressure posed by the amiRNA action on both viral RNA strands causes an evolutionary explosion that results in the emergence of a broad range of virus variants, which can further expand in the presence, and even in the absence, of antiviral challenges.

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

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

Challenges and opportunities for plant viruses under a climate change scenario

There is an increasing societal awareness on the enormous threat that climate change may pose for human, animal and plant welfare. Although direct effects due to exposure to heat, drought or elevated greenhouse gasses seem to be progressively more obvious, indirect effects remain debatable. A relevant aspect to be clarified relates to the relationship between altered environmental conditions and pathogen-induced diseases. In the particular case of plant viruses, it is still unclear whether climate change will primarily represent an opportunity for the emergence of new infections in previously uncolonized areas and hosts, or if it will mostly be a strong constrain reducing the impact of plant virus diseases and challenging the pathogen's adaptive capacity. This review focuses on current knowledge on the relationship between climate change and the outcome plant-virus interactions. We summarize work done on how this relationship modulates plant virus pathogenicity, between-host transmission (which include the triple interaction plant-virus-vector), ecology, evolution and management of the epidemics they cause. Considering these studies, we propose avenues for future research on this subject.

Perspectives on plant virus diseases in a climate change scenario of elevated temperatures

Global food production is at risk from many abiotic and biotic stresses and can be affected by multiple stresses simultaneously. Virus diseases damage cultivated plants and decrease the marketable quality of produce. Importantly, the progression of virus diseases is strongly affected by changing climate conditions. Among climate-changing variables, temperature increase is viewed as an important factor that affects virus epidemics, which may in turn require more efficient disease management. In this review, we discuss the effect of elevated temperature on virus epidemics at both macro- and micro-climatic levels. This includes the temperature effects on virus spread both within and between host plants. Furthermore, we focus on the involvement of molecular mechanisms associated with temperature effects on plant defence to viruses in both susceptible and resistant plants. Considering various mechanisms proposed in different pathosystems, we also offer a view of the possible opportunities provided by RNA -based technologies for virus control at elevated temperatures. Recently, the potential of these technologies for topical field applications has been strengthened through a combination of genetically modified (GM)-free delivery nanoplatforms. This approach represents a promising and important climate-resilient substitute to conventional strategies for managing plant virus diseases under global warming scenarios. In this context, we discuss the knowledge gaps in the research of temperature effects on plant-virus interactions and limitations of RNA-based emerging technologies, which should be addressed in future studies.

Simultaneously induced mutations in eIF4E genes by CRISPR/Cas9 enhance PVY resistance in tobacco

Tobacco is an important commercial crop and a rich source of alkaloids for pharmaceutical and agricultural applications. However, its yield can be reduced by up to 70% due to virus infections, especially by a potyvirus Potato virus Y (PVY). The replication of PVY relies on host factors, and eukaryotic translation initiation factor 4Es (eIF4Es) have already been identified as recessive resistance genes against potyviruses in many plant species. To investigate the molecular basis of PVY resistance in the widely cultivated allotetraploid tobacco variety K326, we developed a dual guide RNA CRISPR/Cas9 system for combinatorial gene editing of two clades, eIF4E1 (eIF4E1-S and eIF4E1-T) and eIF4E2 (eIF4E2-S and eIF4E2-T) in the eIF4E gene family comprising six members in tobacco. We screened for CRISPR/Cas9-induced mutations by heteroduplex analysis and Sanger sequencing, and monitored PVY^O accumulation in virus challenged regenerated plants by DAS-ELISA both in T0 and T1 generations. We found that all T0 lines carrying targeted mutations in the eIF4E1-S gene displayed enhanced resistance to PVY^O confirming previous reports. More importantly, our combinatorial approach revealed that eIF4E1-S is necessary but not sufficient for complete PVY resistance. Only the quadruple mutants harboring loss-of-function mutations in eIF4E1-S, eIF4E1-T, eIF4E2-S and eIF4E2-T showed heritable high-level resistance to PVY^O in tobacco. Our work highlights the importance of understanding host factor redundancy in virus replication and provides a roadmap to generate virus resistance by combinatorial CRISPR/Cas9-mediated editing in non-model crop plants with complex genomes.

Virus Elimination from Naturally Infected Field Cultivars of Potato (Solanum tuberosum) by Transgenic RNA Interference

Tissue culture methods enable virus elimination from vegetatively propagated crop plants but cannot prevent new infections. Here we used a tissue culture transgenic approach for curing field cultivars of Solanum tuberosum through the stimulation of RNA interference (RNAi)-based antiviral defenses. Expression cassettes carrying inverted repeats of potato virus S (PVS, genus Carlavirus) movement or coat protein sequences were used for the transformation of potato cultivars naturally infected with PVS and/or a related carlavirus potato virus M (PVM), without or with potato virus Y (PVY, genus Potyvirus). A high proportion of transformants PCR-positive for transgenes were cured from both carlaviruses and PVY. After 3-year field trials, 22 transgenic lines representing seven cultivars remained free of any virus or became infected only with PVY. Vegetative progenies of the transgenic lines of cultivar Zeren (initially coinfected with PVS, PVM, and PVY), sampled after in vitro propagation or field trials, and other field cultivars accumulated transgene-derived 21, 22, and 24 nt small interfering (si)RNAs almost exclusively from the PVS inverted repeats. Additionally, some field progenies accumulated 21–22 nt siRNAs from the entire PVY genome, confirming PVY infection. Taken together, transgenic RNAi is effective for virus elimination from naturally infected potato cultivars and their sequence-specific immunization against new infections.

Low-cost alternative for the bioproduction of bioactive phenolic compounds of callus cultures from Cereus hildmannianus (K.) Schum

The aim of this study was to establish a sustainable alternative callus culture of Cereus hildmannianus for the production and bioactive determination of phenolic compounds from this species. The conventional callus was cultivated using agar and Murashige and Skoog (MS) medium, while for the alternative culture the agar was replaced with a cotton support covered with filter paper and MS medium (incubated at 32°C with photoperiod of 16h), and the morphological characteristics and growth index were assessed (8 weeks). Extracts were obtained by maceration followed by partition, characterized by nuclear magnetic resonance - NMR and ultra-high performance liquid chromatography - UHPLC, quantified (phenolic compounds) by UV-Vis methods, and their antioxidant, antitumor activities, as well as cytotoxicity, were evaluated. The establishment of an alternative callus culture was carried out successfully. Characteristic signals of phenolic compounds were determined by NMR, and 46 compounds with fragment ions were identified using UHPLC analysis. The highest concentrations of phenolic compounds, and greatest antioxidant and antitumor activities, were obtained with the dichloromethane fractions of both callus tissue cultures, which were not cytotoxic. The callus culture from C. hildmannianus has shown promise as a source for the sustainable production of phenolic compounds with antioxidant and antiproliferative activities and thus, has potential use as a natural antitumor product.

Transcriptomics Advancement in the Complex Response of Plants to Viroid Infection

Viroids are the smallest plant pathogens, consisting of a single-stranded circular RNA of less than 500 ribonucleotides in length. Despite their noncoding nature, viroids elicit disease symptoms in many economically important plant hosts, and are, thus, a class of pathogens of great interest. How these viroids establish disease within host plants, however, is not yet fully understood. Recent transcriptomic studies have revealed that viroid infection influences the expression of genes in several pathways and processes in plants, including defence responses, phytohormone signalling, cell wall modification, photosynthesis, secondary metabolism, transport, gene expression and protein modification. There is much debate about whether affected pathways signify a plant response to viroid infection, or are associated with the appearance of disease symptoms in these interactions. In this review, we consolidate the findings of viroid–host transcriptome studies to provide an overview of trends observed in the data. When considered together, changes in the gene expression of different hosts upon viroid infection reveal commonalities and differences in diverse interactions. Here, we discuss whether trends in host gene expression can be correlated to plant defence or disease development during viroid infection, and highlight avenues for future research in this field.

RNA Interference: Promising Approach to Combat Plant Viruses

Plant viruses are devastating plant pathogens that severely affect crop yield and quality. Plants have developed multiple lines of defense systems to combat viral infection. Gene silencing/RNA interference is the key defense system in plants that inhibits the virulence and multiplication of pathogens. The general mechanism of RNAi involves (i) the transcription and cleavage of dsRNA into small RNA molecules, such as microRNA (miRNA), or small interfering RNA (siRNA), (ii) the loading of siRNA/miRNA into an RNA Induced Silencing Complex (RISC), (iii) complementary base pairing between siRNA/miRNA with a targeted gene, and (iv) the cleavage or repression of a target gene with an Argonaute (AGO) protein. This natural RNAi pathway could introduce transgenes targeting various viral genes to induce gene silencing. Different RNAi pathways are reported for the artificial silencing of viral genes. These include Host-Induced Gene Silencing (HIGS), Virus-Induced Gene Silencing (VIGS), and Spray-Induced Gene Silencing (SIGS). There are significant limitations in HIGS and VIGS technology, such as lengthy and time-consuming processes, off-target effects, and public concerns regarding genetically modified (GM) transgenic plants. Here, we provide in-depth knowledge regarding SIGS, which efficiently provides RNAi resistance development against targeted genes without the need for GM transgenic plants. We give an overview of the defense system of plants against viral infection, including a detailed mechanism of RNAi, small RNA molecules and their types, and various kinds of RNAi pathways. This review will describe how RNA interference provides the antiviral defense, recent improvements, and their limitations.

A spotlight on non-host resistance to plant viruses

Plant viruses encounter a range of host defenses including non-host resistance (NHR), leading to the arrest of virus replication and movement in plants. Viruses have limited host ranges, and adaptation to a new host is an atypical phenomenon. The entire genotypes of plant species which are imperceptive to every single isolate of a genetically variable virus species are described as non-hosts. NHR is the non-specific resistance manifested by an innately immune non-host due to pre-existing and inducible defense responses, which cannot be evaded by yet-to-be adapted plant viruses. NHR-to-plant viruses are widespread, but the phenotypic variation is often not detectable within plant species. Therefore, molecular and genetic mechanisms of NHR need to be systematically studied to enable exploitation in crop protection. This article comprehensively describes the possible mechanisms of NHR against plant viruses. Also, the previous definition of NHR to plant viruses is insufficient, and the main aim of this article is to sensitize plant pathologists to the existence of NHR to plant viruses and to highlight the need for immediate and elaborate research in this area.

CRISPR/Cas-Mediated Resistance against Viruses in Plants

CRISPR/Cas9 provides a robust and widely adaptable system with enormous potential for genome editing directed towards generating useful products. It has been used extensively to generate resistance against viruses infecting plants with more effective and prolonged efficiency as compared with previous antiviral approaches, thus holding promise to alleviate crop losses. In this review, we have discussed the reports of CRISPR/Cas-based virus resistance strategies against plant viruses. These strategies include approaches targeting single or multiple genes (or non-coding region) in the viral genome and targeting host factors essential for virus propagation. In addition, the utilization of base editing has been discussed to generate transgene-free plants resistant to viruses. This review also compares the efficiencies of these approaches. Finally, we discuss combinatorial approaches, including multiplexing, to increase editing efficiency and bypass the generation of escape mutants.

Engineering CRISPR immune systems conferring GLRaV-3 resistance in grapevine

Grapevine leafroll-associated virus 3 (GLRaV-3) is one of the causal agents of grapevine leafroll disease (GLD), which severely impacts grapevine production in most viticultural regions of the world. The development of virus-resistant plants is a desirable strategy for the efficient control of viral diseases. However, natural resistant resources have not been reported in the genus Vitis, and anti-GLRaV-3 research has been quite limited in grapevine. In this study, by expressing FnCas9 and LshCas13a, we established a highly effective transgenic construct screening system via an optimized Agrobacterium-mediated transient delivery system in grapevine plantlets. Our study indicated that CRISPR/FnCas9 and LshCas13a caused GLRaV-3 inhibition. Moreover, three vectors-pCR01-CP, pCR11-Hsp70h and pCR11-CP-exhibited the most robust inhibition efficiency compared to those targeting other sites and could be further engineered to generate GLRaV-3-resistant grapevine. In addition, the viral interference efficiency of FnCas9 was dependent on its RNA binding activity. The efficiency of virus inhibition was positively correlated with the level of Cas gene expression. Importantly, we demonstrated that LshCas13a had better interference efficiency against viruses than FnCas9. In summary, this study confirmed that these two RNA-targeting CRISPR mechanisms can confer immunity against viruses in grapevine, providing new avenues to control GLRaV-3 or other RNA viruses in fruit crops.

Direct Foliar Application of dsRNA Derived From the Full-Length Gene of NSs of Groundnut Bud Necrosis Virus Limits Virus Accumulation and Symptom Expression

Groundnut bud necrosis virus (GBNV) is the most significant member of the genus Orthotospovirus occurring in the Indian subcontinent. There is hardly any effective measure to prevent GBNV in crop plants. In order to develop GBNV infection prevention procedure, we examined the effect of the direct foliar application of double-stranded RNA (dsRNA) derived from the full-length NSs gene (1,320 nucleotides) of GBNV. The bacterially expressed dsRNA to the non-structural (dsNSs) gene of GBNV was purified and delivered to plants as an aqueous suspension containing 0.01% Celite for evaluating its efficacy in preventing GBNV infection in systemic host, Nicotiana benthamiana as well as in local lesion and systemic host, cowpea cv. Pusa Komal (Vigna unguiculata). The dsNSs application and challenge-inoculation were conducted in three different combinations, where plants were challenge-inoculated with GBNV a day after, immediately, and a day before the application of dsNSs. N. benthamiana plants, which were not treated with dsRNA showed severe systemic wilting and death by 9-16 days post-inoculation (dpi). The non-treated cowpea plants exhibited many chlorotic and necrotic lesions on the cotyledonary leaves followed by systemic necrosis and death of the plants by 14-16 dpi. The dsNSs treated plants in all the combinations showed significant reduction of disease severity index in both N. benthamiana and cowpea. The treatment combination where the GBNV inoculation was conducted immediately after the dsNSs treatment was found to be the most effective treatment in preventing symptom expression. The viral RNA analysis by real time PCR also showed 20 and 12.5 fold reduction of GBNV in cowpea and N. benthamiana, respectively. Our results suggest that the foliar application of dsRNA derived from the full-length NSs gene of GBNV through Celite is successful in delivering long dsRNA leading to effective prevention of GBNV infection.

A status-quo review on CRISPR-Cas9 gene editing applications in tomato

Epigenetic changes are emancipated in horticultural crops including tomato due to a variety of environmental factors. These modifications rely on plant phenotypes mediated by genetic architecture consequently resulting in hereditary epigenetic memory. Genome editing strategies like CRISPR (Clustered Regularly Interspaced Short Palindromic Repeat)/CRISPR-associated protein 9 (Cas9) technologies have revolutionized plants biology foreseeing stable inheritance of epigenetic modifications. CRISPR/Cas9 strategy poses as explicit advancement in providing precise genome editing with minimal off-target mutations, ease of experimental design, higher efficiency, versatility, and cost-effectiveness. Dicot crops, especially tomato remain an ideal candidate for CRISPR/Cas9 based gene modulations thereby augmenting productivity and yields. In the present review, key questions on CRISPR/Cas9 applications aid in enhanced growth based on optimal gene discovery, de novo modification, trait improvement, and biotic/abiotic stress management are discussed. In addition, comparative scenario in tomato and similar horticultural crops are adequately summarized for the pros and cons. Further, limitations hampering potential benefits and success phenomena of the lab to field transition of gene editing alterations are discussed collaterally in addressing futuristic optimization for CRISPR/Cas9 research in tomato.

Integrating CRISPR-Cas and Next Generation Sequencing in Plant Virology

Plant pathology has been revolutionized by the emergence and intervention of next-generation sequencing technologies (NGS) which provide a fast, cost-effective, and reliable diagnostic for any class of pathogens. NGS has made tremendous advancements in the area of research and diagnostics of plant infecting viromes and has bridged plant virology with other advanced research fields like genome editing technologies. NGS in a broader perspective holds the potential for plant health improvement by diagnosing and mitigating the new or unusual symptoms caused by novel/unidentified viruses. CRISPR-based genome editing technologies can enable rapid engineering of efficient viral/viroid resistance by directly targeting specific nucleotide sites of plant viruses and viroids. Critical genes such as eIf (iso) 4E or eIF4E have been targeted via the CRISPR platform to produce plants resistant to single-stranded RNA (ssRNA) viruses. CRISPR/Cas-based multi-target DNA or RNA tests can be used for rapid and accurate diagnostic assays for plant viruses and viroids. Integrating NGS with CRISPR-based genome editing technologies may lead to a paradigm shift in combating deadly disease-causing plant viruses/viroids at the genomic level. Furthermore, the newly discovered CRISPR/Cas13 system has unprecedented potential in plant viroid diagnostics and interference. In this review, we have highlighted the application and importance of sequencing technologies on covering the viral genomes for precise modulations. This review also provides a snapshot vision of emerging developments in NGS technologies for the characterization of plant viruses and their potential utilities, advantages, and limitations in plant viral diagnostics. Furthermore, some of the notable advances like novel virus-inducible CRISPR/Cas9 system that confers virus resistance with no off-target effects have been discussed.

Virus Diseases of Cereal and Oilseed Crops in Australia: Current Position and Future Challenges

This review summarizes research on virus diseases of cereals and oilseeds in Australia since the 1950s. All viruses known to infect the diverse range of cereal and oilseed crops grown in the continent's temperate, Mediterranean, subtropical and tropical cropping regions are included. Viruses that occur commonly and have potential to cause the greatest seed yield and quality losses are described in detail, focusing on their biology, epidemiology and management. These are: barley yellow dwarf virus, cereal yellow dwarf virus and wheat streak mosaic virus in wheat, barley, oats, triticale and rye; Johnsongrass mosaic virus in sorghum, maize, sweet corn and pearl millet; turnip yellows virus and turnip mosaic virus in canola and Indian mustard; tobacco streak virus in sunflower; and cotton bunchy top virus in cotton. The currently less important viruses covered number nine infecting nine cereal crops and 14 infecting eight oilseed crops (none recorded for rice or linseed). Brief background information on the scope of the Australian cereal and oilseed industries, virus epidemiology and management and yield loss quantification is provided. Major future threats to managing virus diseases effectively include damaging viruses and virus vector species spreading from elsewhere, the increasing spectrum of insecticide resistance in insect and mite vectors, resistance-breaking virus strains, changes in epidemiology, virus and vectors impacts arising from climate instability and extreme weather events, and insufficient industry awareness of virus diseases. The pressing need for more resources to focus on addressing these threats is emphasized and recommendations over future research priorities provided.

Genetic identification and characterization of chromosomal regions for kernel length and width increase from tetraploid wheat

BACKGROUND

Improvement of wheat gercTriticum aestivum L.) yield could relieve global food shortages. Kernel size, as an important component of 1000-kernel weight (TKW), is always a significant consideration to improve yield for wheat breeders. Wheat related species possesses numerous elite genes that can be introduced into wheat breeding. It is thus vital to explore, identify, and introduce new genetic resources for kernel size from wheat wild relatives to increase wheat yield.

RESULTS

In the present study, quantitative trait loci (QTL) for kernel length (KL) and width (KW) were detected in a recombinant inbred line (RIL) population derived from a cross between a wild emmer accession 'LM001' and a Sichuan endemic tetraploid wheat 'Ailanmai' using the Wheat 55 K single nucleotide polymorphism (SNP) array-based constructed linkage map and phenotype from six different environments. We identified eleven QTL for KL and KW including two major ones QKL.sicau-AM-3B and QKW.sicau-AM-4B, the positive alleles of which were from LM001 and Ailanmai, respectively. They explained 17.57 to 44.28% and 13.91 to 39.01% of the phenotypic variance, respectively. For these two major QTL, Kompetitive allele-specific PCR (KASP) markers were developed and used to successfully validate their effects in three F3 populations and two natural populations containing a panel of 272 Chinese wheat landraces and that of 300 Chinese wheat cultivars, respectively. QKL.sicau-AM-3B was located at 675.6-695.4 Mb on chromosome arm 3BL. QKW.sicau-AM-4B was located at 444.2-474.0 Mb on chromosome arm 4BL. Comparison with previous studies suggested that these two major QTL were likely new loci. Further analysis indicated that the positive alleles of QKL.sicau-AM-3B and QKW.sicau-AM-4B had a great additive effect increasing TKW by 6.01%. Correlation analysis between KL and other agronomic traits showed that KL was significantly correlated to spike length, length of uppermost internode, TKW, and flag leaf length. KW was also significantly correlated with TKW. Four genes, TRIDC3BG062390, TRIDC3BG062400, TRIDC4BG037810, and TRIDC4BG037830, associated with kernel development were predicted in physical intervals harboring these two major QTL on wild emmer and Chinese Spring reference genomes.

CONCLUSIONS

Two stable and major QTL for KL and KW across six environments were detected and verified in three biparental populations and two natural populations. Significant relationships between kernel size and yield-related traits were identified. KASP markers tightly linked the two major QTL could contribute greatly to subsequent fine mapping. These results suggested the application potential of wheat related species in wheat genetic improvement.

Perfecting Targeting in CRISPR

CRISPR-based genome editing holds promise for genome engineering and other applications in diverse organisms. Defining and improving the genome-wide and transcriptome-wide specificities of these editing tools are essential for realizing their full potential in basic research and biomedical therapeutics. This review provides an overview of CRISPR-based DNA- and RNA-editing technologies, methods to quantify their specificities, and key solutions to reduce off-target effects for research and improve therapeutic applications. Expected final online publication date for the Annual Review of Genetics, Volume 55 is November 2021. Please see http://www.annualreviews.org/page/journal/pubdates for revised estimates.

Versatile Applications of the CRISPR/Cas Toolkit in Plant Pathology and Disease Management

New tools and advanced technologies have played key roles in facilitating basic research in plant pathology and practical approaches for disease management and crop health. Recently, the CRISPR/Cas (clustered regularly interspersed short palindromic repeats/CRISPR-associated) system has emerged as a powerful and versatile tool for genome editing and other molecular applications. This review aims to introduce and highlight the CRISPR/Cas toolkit and its current and future impact on plant pathology and disease management. We will cover the rapidly expanding horizon of various CRISPR/Cas applications in the basic study of plant-pathogen interactions, genome engineering of plant disease resistance, and molecular diagnosis of diverse pathogens. Using the citrus greening disease as an example, various CRISPR/Cas-enabled strategies are presented to precisely edit the host genome for disease resistance, to rapidly detect the pathogen for disease management, and to potentially use gene drive for insect population control. At the cutting edge of nucleic acid manipulation and detection, the CRISPR/Cas toolkit will accelerate plant breeding and reshape crop production and disease management as we face the challenges of 21st century agriculture.

Control of Plant Viral Diseases by CRISPR/Cas9: Resistance Mechanisms, Strategies and Challenges in Food Crops

Protecting food crops from viral pathogens is a significant challenge for agriculture. An integral approach to genome-editing, known as CRISPR/Cas9 (clustered regularly interspaced short palindromic repeats and CRISPR associated protein 9), is used to produce virus-resistant cultivars. The CRISPR/Cas9 tool is an essential part of modern plant breeding due to its attractive features. Advances in plant breeding programs due to the incorporation of Cas9 have enabled the development of cultivars with heritable resistance to plant viruses. The resistance to viral DNA and RNA is generally provided using the Cas9 endonuclease and sgRNAs (single-guide RNAs) complex, targeting particular virus and host plant genomes by interrupting the viral cleavage or altering the plant host genome, thus reducing the replication ability of the virus. In this review, the CRISPR/Cas9 system and its application to staple food crops resistance against several destructive plant viruses are briefly described. We outline the key findings of recent Cas9 applications, including enhanced virus resistance, genetic mechanisms, research strategies, and challenges in economically important and globally cultivated food crop species. The research outcome of this emerging molecular technology can extend the development of agriculture and food security. We also describe the information gaps and address the unanswered concerns relating to plant viral resistance mediated by CRISPR/Cas9.

Roles of Plant Glycine-Rich RNA-Binding Proteins in Development and Stress Responses

In recent years, much progress has been made in elucidating the functional roles of plant glycine-rich RNA-binding proteins (GR-RBPs) during development and stress responses. Canonical GR-RBPs contain an RNA recognition motif (RRM) or a cold-shock domain (CSD) at the N-terminus and a glycine-rich domain at the C-terminus, which have been associated with several different RNA processes, such as alternative splicing, mRNA export and RNA editing. However, many aspects of GR-RBP function, the targeting of their RNAs, interacting proteins and the consequences of the RNA target process are not well understood. Here, we discuss recent findings in the field, newly defined roles for GR-RBPs and the actions of GR-RBPs on target RNA metabolism.

Genomic Approaches to Identify Molecular Bases of Crop Resistance to Diseases and to Develop Future Breeding Strategies

Plant diseases are responsible for substantial crop losses each year and affect food security and agricultural sustainability. The improvement of crop resistance to pathogens through breeding represents an environmentally sound method for managing disease and minimizing these losses. The challenge is to breed varieties with a stable and broad-spectrum resistance. Different approaches, from markers to recent genomic and 'post-genomic era' technologies, will be reviewed in order to contribute to a better understanding of the complexity of host-pathogen interactions and genes, including those with small phenotypic effects and mechanisms that underlie resistance. An efficient combination of these approaches is herein proposed as the basis to develop a successful breeding strategy to obtain resistant crop varieties that yield higher in increasing disease scenarios.

Application of CRISPR/Cas for Diagnosis and Management of Viral Diseases of Banana

Viral diseases are significant biotic constraints for banana (Musa spp.) production as they affect the yield and limit the international movement of germplasm. Among all the viruses known to infect banana, the banana bunchy top virus and banana streak viruses are widespread and economically damaging. The use of virus-resistant bananas is the most cost-effective option to minimize the negative impacts of viral-diseases on banana production. CRISPR/Cas-based genome editing is emerging as the most powerful tool for developing virus-resistant crop varieties in several crops, including the banana. The availability of a vigorous genetic transformation and regeneration system and a well-annotated whole-genome sequence of banana makes it a compelling candidate for genome editing. A robust CRISPR/Cas9-based genome editing of the banana has recently been established, which can be applied in developing disease-resistant varieties. Recently, the CRISPR system was exploited to detect target gene sequences using Cas9, Cas12, Cas13, and Cas14 enzymes, thereby unveiling the use of this technology for virus diagnosis. This article presents a synopsis of recent advancements and perspectives on the application of CRISPR/Cas-based genome editing for diagnosing and developing resistance against banana viruses and challenges in genome-editing of banana.

RNA-Based Technologies for Engineering Plant Virus Resistance

In recent years, non-coding RNAs (ncRNAs) have gained unprecedented attention as new and crucial players in the regulation of numerous cellular processes and disease responses. In this review, we describe how diverse ncRNAs, including both small RNAs and long ncRNAs, may be used to engineer resistance against plant viruses. We discuss how double-stranded RNAs and small RNAs, such as artificial microRNAs and trans-acting small interfering RNAs, either produced in transgenic plants or delivered exogenously to non-transgenic plants, may constitute powerful RNA interference (RNAi)-based technology that can be exploited to control plant viruses. Additionally, we describe how RNA guided CRISPR-CAS gene-editing systems have been deployed to inhibit plant virus infections, and we provide a comparative analysis of RNAi approaches and CRISPR-Cas technology. The two main strategies for engineering virus resistance are also discussed, including direct targeting of viral DNA or RNA, or inactivation of plant host susceptibility genes. We also elaborate on the challenges that need to be overcome before such technologies can be broadly exploited for crop protection against viruses.

Understanding the Plant-microbe Interactions in CRISPR/CAS9 Era: Indeed a Sprinting Start in Marathon

Plant-microbe interactions can be either beneficial or harmful depending on the nature of the interaction. Multifaceted benefits of plant-associated microbes in crops are well documented. Specifically, the management of plant diseases using beneficial microbes is considered to be eco-friendly and the best alternative for sustainable agriculture. Diseases caused by various phytopathogens are responsible for a significant reduction in crop yield and cause substantial economic losses globally. In an ecosystem, there is always an equally daunting challenge for the establishment of disease and development of resistance by pathogens and plants, respectively. In particular, comprehending the complete view of the complex biological systems of plant-pathogen interactions, co-evolution and plant growth promotions (PGP) at both genetic and molecular levels requires novel approaches to decipher the function of genes involved in their interaction. The Clustered Regularly Interspaced Short Palindromic Repeats (CRISPR)/Cas9 (CRISPR-associated protein 9) is a fast, emerging, precise, eco-friendly and efficient tool to address the challenges in agriculture and decipher plant-microbe interaction in crops. Nowadays, the CRISPR/CAS9 approach is receiving major attention in the field of functional genomics and crop improvement. Consequently, the present review updates the prevailing knowledge in the deployment of CRISPR/CAS9 techniques to understand plant-microbe interactions, genes edited for the development of fungal, bacterial and viral disease resistance, to elucidate the nodulation processes, plant growth promotion, and future implications in agriculture. Further, CRISPR/CAS9 would be a new tool for the management of plant diseases and increasing productivity for climate resilience farming.

Precision Breeding Made Real with CRISPR: Illustration through Genetic Resistance to Pathogens

Since its discovery as a bacterial adaptive immune system and its development for genome editing in eukaryotes, the CRISPR technology has revolutionized plant research and precision crop breeding. The CRISPR toolbox holds great promise in the production of crops with genetic disease resistance to increase agriculture resilience and reduce chemical crop protection with a strong impact on the environment and public health. In this review, we provide an extensive overview on recent breakthroughs in CRISPR technology, including the newly developed prime editing system that allows precision gene editing in plants. We present how each CRISPR tool can be selected for optimal use in accordance with its specific strengths and limitations, and illustrate how the CRISPR toolbox can foster the development of genetically pathogen-resistant crops for sustainable agriculture.