Efficient generation of mutations mediated by CRISPR/Cas9 in the hairy root transformation system of Brassica carinata

Advancing vegetable genetics with gene editing: a pathway to food security and nutritional resilience in climate-shifted environments

As global populations grow and climate change increasingly disrupts agricultural systems, ensuring food security and nutritional resilience has become a critical challenge. In addition to grains and legumes, vegetables are very important for both human and animals because they contain vitamins, minerals, and fibre. Enhancing the ability of vegetables to withstand climate change threats is essential; however, traditional breeding methods face challenges due to the complexity of the genomic clonal multiplication process. In the postgenomic era, gene editing (GE) has emerged as a powerful tool for improving vegetables. GE can help to increase traits such as abiotic stress tolerance, herbicide tolerance, and disease resistance; improve agricultural productivity; and improve nutritional content and shelf-life by fine-tuning key genes. GE technologies such as Clustered Regularly Interspaced Short Palindromic Repeats/CRISPR-associated protein 9 (CRISPR-Cas9) have revolutionized vegetable breeding by enabling specific gene modifications in the genome. This review highlights recent advances in CRISPR-mediated editing across various vegetable species, highlighting successful modifications that increase their resilience to climatic stressors. Additionally, it explores the potential of GE to address malnutrition by increasing the nutrient content of vegetable crops, thereby contributing to public health and food system sustainability. Additionally, it addresses the implementation of GE-guided breeding strategies in agriculture, considering regulatory, ethical, and public acceptance issues. Enhancing vegetable genetics via GE may provide a reliable and nutritious food supply for an expanding global population under more unpredictable environmental circumstances.

Improvement of crop production in controlled environment agriculture through breeding

Controlled environment agriculture (CEA) represents one of the fastest-growing sectors of horticulture. Production in controlled environments ranges from highly controlled indoor environments with 100% artificial lighting (vertical farms or plant factories) to high-tech greenhouses with or without supplemental lighting, to simpler greenhouses and high tunnels. Although food production occurs in the soil inside high tunnels, most CEA operations use various hydroponic systems to meet crop irrigation and fertility needs. The expansion of CEA offers promise as a tool for increasing food production in and near urban systems as these systems do not rely on arable agricultural land. In addition, CEA offers resilience to climate instability by growing inside protective structures. Products harvested from CEA systems tend to be of high quality, both internal and external, and are sought after by consumers. Currently, CEA producers rely on cultivars bred for production in open-field agriculture. Because of high energy and other production costs in CEA, only a limited number of food crops have proven themselves to be profitable to produce. One factor contributing to this situation may be a lack of optimized cultivars. Indoor growing operations offer opportunities for breeding cultivars that are ideal for these systems. To facilitate breeding these specialized cultivars, a wide range of tools are available for plant breeders to help speed this process and increase its efficiency. This review aims to cover breeding opportunities and needs for a wide range of horticultural crops either already being produced in CEA systems or with potential for CEA production. It also reviews many of the tools available to breeders including genomics-informed breeding, marker-assisted selection, precision breeding, high-throughput phenotyping, and potential sources of germplasm suitable for CEA breeding. The availability of published genomes and trait-linked molecular markers should enable rapid progress in the breeding of CEA-specific food crops that will help drive the growth of this industry.

Imaging of plant calcium-sensor kinase conformation monitors real time calcium-dependent decoding in planta

Changes in cytosolic calcium (Ca2+) concentration are among the earliest reactions to a multitude of stress cues. While a plethora of Ca2+-permeable channels may generate distinct Ca2+ signatures and contribute to response specificities, the mechanisms by which Ca2+ signatures are decoded are poorly understood. Here, we developed a genetically encoded Förster resonance energy transfer (FRET)-based reporter that visualizes the conformational changes in Ca2+-dependent protein kinases (CDPKs/CPKs). We focused on two CDPKs with distinct Ca2+-sensitivities, highly Ca2+-sensitive Arabidopsis (Arabidopsis thaliana) AtCPK21 and rather Ca2+-insensitive AtCPK23, to report conformational changes accompanying kinase activation. In tobacco (Nicotiana tabacum) pollen tubes, which naturally display coordinated spatial and temporal Ca2+ fluctuations, CPK21-FRET, but not CPK23-FRET, reported oscillatory emission ratio changes mirroring cytosolic Ca2+ changes, pointing to the isoform-specific Ca2+-sensitivity and reversibility of the conformational change. In Arabidopsis guard cells, CPK21-FRET-monitored conformational dynamics suggest that CPK21 serves as a decoder of signal-specific Ca2+ signatures in response to abscisic acid and the flagellin peptide flg22. Based on these data, CDPK-FRET is a powerful approach for tackling real-time live-cell Ca2+ decoding in a multitude of plant developmental and stress responses.

New insights into the genetic manipulation of the R2R3-MYB and CHI gene families on anthocyanin pigmentation in Petunia hybrida

Several R2R3-MYB genes control anthocyanin pigmentation in petunia, and ANTHOCYANIN-2 (AN2) is treated as the main player in petal limbs. However, the actual roles of R2R3-MYBs in the coloration of different floral tissues in the so called "darkly-veined" petunias are still not clear. The genetic background and expression of AN2 paralogs from various petunias with different color patterns were identified. All "darkly-veined" genotypes have the identical mutation in the AN2 gene, but express a different functional paralog - ANTHOCYANIN-4 (AN4) - abundantly in flowers. Constitutive overexpression of PhAN4 in this petunia resulted not only in a fully colored flower but also in a clearly visible pigmentation in the green tissue and roots, which can be rapidly increased by stress conditions. Suppression of AN4 gene resulted in discolored petals and whitish anthers. Interestingly, when a similar white flower phenotype was achieved by knockout of an essential structural gene of anthocyanin biosynthesis - CHALCONE ISOMERASE-A (CHI-A) - the plant responded directly by upregulating of another paralogs - DEEP PURPLE (DPL) and PURPLE HAZE (PHZ). Moreover, we also found that CHI-B can partially substitute for CHI-A in anthers, but not in vegetative tissues. Further, no significant effects on the longevity of white or enhanced colored flowers were observed compared with the wild type. We concluded that endogenous up-regulation of AN4 leads to the restoration of petal color in the "darkly-veined" phenotypes as a result of the breeding process under human selection, and CHI-B is a backup for CHI-A acitvity in some floral tissues.

The current scenario and future perspectives of transgenic oilseed mustard by CRISPR-Cas9

PURPOSE

Production of a designer crop having added attributes is the primary goal of all plant biotechnologists. Specifically, development of a crop with a simple biotechnological approach and at a rapid pace is most desirable. Genetic engineering enables us to displace genes among species. The newly incorporated foreign gene(s) in the host genome can create a new trait(s) by regulating the genotypes and/or phenotypes. The advent of the CRISPR-Cas9 tools has enabled the modification of a plant genome easily by introducing mutation or replacing genomic fragment. Oilseed mustard varieties (e.g., Brassica juncea, Brassica nigra, Brassica napus, and Brassica carinata) are one such plants, which have been transformed with different genes isolated from the wide range of species. Current reports proved that the yield and value of oilseed mustard has been tremendously improved by the introduction of stably inherited new traits such as insect and herbicide resistance. However, the genetic transformation of oilseed mustard remains incompetent due to lack of potential plant transformation systems. To solve numerous complications involved in genetically modified oilseed mustard crop varieties regeneration procedures, scientific research is being conducted to rectify the unwanted complications. Thus, this study provides a broader overview of the present status of new traits introduced in each mentioned varieties of oilseed mustard plant by different genetical engineering tools, especially CRISPR-Cas9, which will be useful to improve the transformation system of oilseed mustard crop plants.

METHODS

This review presents recent improvements made in oilseed mustard genetic engineering methodologies by using CRISPR-Cas9 tools, present status of new traits introduced in oilseed mustard plant varieties.

RESULTS

The review highlighted that the transgenic oilseed mustard production is a challenging process and the transgenic varieties of oilseed mustard provide a powerful tool for enhanced mustard yield. Over expression studies and silencing of desired genes provide functional importance of genes involved in mustard growth and development under different biotic and abiotic stress conditions. Thus, it can be expected that in near future CRISPR can contribute enormously in improving the mustard plant's architecture and develop stress resilient oilseed mustard plant species.

Role of BraRGL1 in regulation of Brassica rapa bolting and flowering

Gibberellin (GA) plays a major role in controlling Brassica rapa stalk development. As an essential negative regulator of GA signal transduction, DELLA proteins may exert significant effects on stalk development. However, the regulatory mechanisms underlying this regulation remain unclear. In this study, we report highly efficient and inheritable mutagenesis using the CRISPR/Cas9 gene editing system in BraPDS (phytoene desaturase) and BraRGL1 (key DELLA protein) genes. We observed a loss-of-function mutation in BraRGL1 due to two amino acids in GRAS domain. The flower bud differentiation and bolting time of BraRGL1 mutants were significantly advanced. The expression of GA-regulatory protein (BraGASA6), flowering related genes (BraSOC1, BraLFY), expansion protein (BraEXPA11) and xyloglucan endotransferase (BraXTH3) genes was also significantly upregulated in these mutants. BraRGL1-overexpressing plants displayed the contrasting phenotypes. BraRGL1 mutants were more sensitive to GA signaling. BraRGL1 interacted with BraSOC1, and the interaction intensity decreased after GA3 treatment. In addition, BraRGL1 inhibited the transcription-activation ability of BraSOC1 for BraXTH3 and BraLFY genes, but the presence of GA3 enhanced the activation ability of BraSOC1, suggesting that the BraRGL1-BraSOC1 module regulates bolting and flowering of B. rapa through GA signal transduction. Thus, we hypothesized that BraRGL1 is degraded, and BraSOC1 is released in the presence of GA3, which promotes the expression of BraXTH3 and BraLFY, thereby inducing stalk development in B. rapa. Further, the BraRGL1-M mutant promoted the flower bud differentiation without affecting the stalk quality. Thus, BraRGL1 can serve as a valuable target for the molecular breeding of early maturing varieties.

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.

Key Advances in the New Era of Genomics-Assisted Disease Resistance Improvement of Brassica Species

Disease resistance improvement remains a major focus in breeding programs as diseases continue to devastate Brassica production systems due to intensive cultivation and climate change. Genomics has paved the way to understand the complex genomes of Brassicas, which has been pivotal in the dissection of the genetic underpinnings of agronomic traits driving the development of superior cultivars. The new era of genomics-assisted disease resistance breeding has been marked by the development of high-quality genome references, accelerating the identification of disease resistance genes controlling both qualitative (major) gene and quantitative resistance. This facilitates the development of molecular markers for marker assisted selection and enables genome editing approaches for targeted gene manipulation to enhance the genetic value of disease resistance traits. This review summarizes the key advances in the development of genomic resources for Brassica species, focusing on improved genome references, based on long-read sequencing technologies and pangenome assemblies. This is further supported by the advances in pathogen genomics, which have resulted in the discovery of pathogenicity factors, complementing the mining of disease resistance genes in the host. Recognizing the co-evolutionary arms race between the host and pathogen, it is critical to identify novel resistance genes using crop wild relatives and synthetic cultivars or through genetic manipulation via genome-editing to sustain the development of superior cultivars. Integrating these key advances with new breeding techniques and improved phenotyping using advanced data analysis platforms will make disease resistance improvement in Brassica species more efficient and responsive to current and future demands.

Sequencing and analysis of the complete mitochondrial genomes of Toona sinensis and Toona ciliata reveal evolutionary features of Toona

BACKGROUND

Toona is a critical genus in the Meliaceae, and the plants of this group are an asset for both restorative and restorative purposes, the most flexible of which are Toona sinensis and Toona ciliata. To concentrate on the advancement of mitochondrial(Mt) genome variety in T.sinensis and T.ciliata, the Mt genomes of the two species were sequenced in high throughput independently, after de novo assembly and annotation to construct a Mt genome map for comparison in genome structure. Find their repetitive sequences and analyze them in comparison with the chloroplast genome, along with Maximum-likelihood(ML) phylogenetic analysis with 16 other relatives.

RESULTS

(1) T. sinensis and T.ciliata are both circular structures with lengths of 683482 bp and 68300 bp, respectively. They share a high degree of similarity in encoding genes and have AT preferences. All of them have the largest Phe concentration and are the most frequently used codons. (2) Both of their Mt genome are highly preserved in terms of structural and functional genes, while the main variability is reflected in the length of tRNA, the number of genes, and the value of RSCU. (3) T. siniensis and T. ciliata were detected to have 94 and 87 SSRs, respectively, of which mononucleotides accounted for the absolute proportion. Besides, the vast majority of their SSRs were found to be poly-A or poly-T. (4)10 and 11 migrating fragments were identified in the comparison with the chloroplast genome, respectively. (5) In the ML evolutionary tree, T.sinensis and T.ciliata clustered individually into a small branch with 100% support, reflecting two species of Toona are very similarly related to each other.

CONCLUSIONS

This research provides a basis for the exploitation of T.sinensis and T.ciliata in terms of medicinal, edible, and timber resources to avoid confusion; at the same time, it can explore the evolutionary relationship between the Toona and related species, which does not only have an important practical value, but also provides a theoretical basis for future hybrid breeding of forest trees, molecular markers, and evolutionary aspects of plants, which has great scientific significance.

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.

Enzymes and cellular interplay required for flux of fixed nitrogen to ureides in bean nodules

Tropical legumes transport fixed nitrogen in form of ureides (allantoin and allantoate) over long distances from the nodules to the shoot. Ureides are formed in nodules from purine mononucleotides by a partially unknown reaction network that involves bacteroid-infected and uninfected cells. Here, we demonstrate by metabolic analysis of CRISPR mutant nodules of Phaseolus vulgaris defective in either xanthosine monophosphate phosphatase (XMPP), guanosine deaminase (GSDA), the nucleoside hydrolases 1 and 2 (NSH1, NSH2) or xanthine dehydrogenase (XDH) that nodule ureide biosynthesis involves these enzymes and requires xanthosine and guanosine but not inosine monophosphate catabolism. Interestingly, promoter reporter analyses revealed that XMPP, GSDA and XDH are expressed in infected cells, whereas NSH1, NSH2 and the promoters of the downstream enzymes urate oxidase (UOX) and allantoinase (ALN) are active in uninfected cells. The data suggest a complex cellular organization of ureide biosynthesis with three transitions between infected and uninfected cells.

Tropical legumes export fixed nitrogen from nodules as ureides. Here, the authors describe how ureides are produced by several biosynthetic enzymes in different nodule cell types and provide explanations for metabolic compartmentation.

Hairy root transformation system as a tool for CRISPR/Cas9-directed genome editing in oilseed rape (Brassica napus)

Our study examined the mutation efficiency of the CRISPR/Cas9 method for tryptophan aminotransferase BnaTAA1 genes involved in the auxin biosynthesis pathway. We made nine CRISPR/Cas9 constructs with various promoters driving the expression of a Cas9 from Staphylococcus aureus (SaCas9) or a plant-codon-optimized Streptococcus pyogenes Cas9 (pcoCas9). We developed a fast and efficient system for evaluating the variety and frequency of mutations caused by each construct using Brassica napus hairy roots. We showed that pcoCas9 is more efficient in mutating the targeted loci than SaCas9 and the presence of the NLS signal enhanced the chance of mutagenesis by 25%. The mutations were studied further in regenerated lines, and we determined the BnaTAA1 gene expression and heritability of the gene modifications in transgenic plants. Hairy root transformation combined with CRISPR/Cas9-mediated gene editing represents a fast and straightforward system for studying target gene function in the important oilseed crop B. napus.

The application of CRISPR/Cas technologies to Brassica crops: current progress and future perspectives

Brassica species are a global source of nutrients and edible vegetable oil for humans. However, all commercially important Brassica crops underwent a whole-genome triplication event, hindering the development of functional genomics and breeding programs. Fortunately, clustered regularly interspaced short palindromic repeat (CRISPR)/CRISPR-associated (Cas) technologies, by allowing multiplex and precise genome engineering, have become valuable genome-editing tools and opened up new avenues for biotechnology. Here, we review current progress in the use of CRISPR/Cas technologies with an emphasis on the latest breakthroughs in precise genome editing. We also summarize the application of CRISPR/Cas technologies to Brassica crops for trait improvements. Finally, we discuss the challenges and future directions of these technologies for comprehensive application in Brassica crops. Ongoing advancement in CRISPR/Cas technologies, in combination with other achievements, will play a significant role in the genetic improvement and molecular breeding of Brassica crops.

Improvement of glucosinolates by metabolic engineering in Brassica crops

Glucosinolates (GSLs) are a class of sulfur- and nitrogen-containing, and amino acid-derived important secondary metabolites, which mainly present in plants of Brassicaceae family, including Brassica crops, such as broccoli, cabbage, and oilseed rape. The bioactive GSL metabolites confer benefits to plant defense, human health, and the unique flavor of some Brassica crops. However, certain GSL profiles have adverse effects and are known as anti-nutritional factors. This has attracted mounting attempts to increase beneficial GSLs and reduce detrimental ones in the most commonly consumed Brassica crops. We provide a comprehensive overview of metabolic engineering applied in Brassica crops to achieve this purpose, including modulation of GSL biosynthesis, ablation of GSL hydrolysis, inhibition of GSL transport processes, and redirection of metabolic flux to GSL. Moreover, advances in omics approaches, i.e., genomics, transcriptome, and metabolome, applied in the elucidation of GSL metabolism in Brassica crops, as well as promising and potential genome-editing technologies are also discussed.

CRISPR-Cas9-Mediated Gene Editing of MYB28 Genes Impair Glucoraphanin Accumulation of Brassica oleracea in the Field

Discoveries in model plants grown under optimal conditions can provide important directions for crop improvement. However, it is important to verify whether results can be translated to crop plants grown in the field. In this study, we sought to study the role of MYB28 in the regulation of aliphatic glucosinolate (A-GSL) biosynthesis and associated sulfur metabolism in field-grown Brassica oleracea with the use of Clustered Regularly Interspaced Short Palindromic Repeats (CRISPR)-Cas9 gene-editing technology. We describe the first myb28 knockout mutant in B. oleracea, and the first CRISPR field trial in the United Kingdom approved and regulated by the UK Department for Environment, Food & Rural Affairs after the reclassification of gene-edited crops as genetically modified organisms by the European Court of Justice on July 25, 2018. We report that knocking out myb28 results in downregulation of A-GSL biosynthesis genes and reduction in accumulation of the methionine-derived glucosinolate, glucoraphanin, in leaves and florets of field-grown myb28 mutant broccoli plants, whereas accumulation of sulfate, S-methyl cysteine sulfoxide, and indole glucosinolate in leaf and floret tissues remained unchanged. These results demonstrate the potential of gene-editing approaches to translate discoveries in fundamental biological processes for improved crop performance.

Site-directed mutagenesis by biolistic transformation efficiently generates inheritable mutations in a targeted locus in soybean somatic embryos and transgene-free descendants in the T1 generation

The clustered regularly interspaced short palindromic repeat (CRISPR)/CRISPR-associated endonuclease 9 (Cas9) system is being rapidly developed for mutagenesis in higher plants. Ideally, foreign DNA introduced by this system is removed in the breeding of edible crops and vegetables. Here, we report an efficient generation of Cas9-free mutants lacking an allergenic gene, Gly m Bd 30K, using biolistic transformation and the CRISPR/Cas9 system. Five transgenic embryo lines were selected on the basis of hygromycin resistance. Cleaved amplified polymorphic sequence analysis detected only two different mutations in e all of the lines. These results indicate that mutations were induced in the target gene immediately after the delivery of the exogenous gene into the embryo cells. Soybean plantlets (T0 plants) were regenerated from two of the transgenic embryo lines. The segregation pattern of the Cas9 gene in the T1 generation, which included Cas9-free plants, revealed that a single copy number of transgene was integrated in both lines. Immunoblot analysis demonstrated that no Gly m Bd 30K protein accumulated in the Cas9-free plants. Gene expression analysis indicated that nonsense mRNA decay might have occurred in mature mutant seeds. Due to the efficient induction of inheritable mutations and the low integrated transgene copy number in the T0 plants, we could remove foreign DNA easily by genetic segregation in the T1 generation. Our results demonstrate that biolistic transformation of soybean embryos is useful for CRISPR/Cas9-mediated site-directed mutagenesis of soybean for human consumption.

Gene duplication and stress genomics in Brassicas: Current understanding and future prospects

Polyploidy or whole genome duplication (WGD) is an evolutionary phenomenon that happened in all angiosperms multiple times over millions of years. Extensive studies on the model plant Arabidopsis thaliana genome have revealed that it has undergone five rounds of WGDs followed, in the Brassicaceae tribe, by a characteristic whole genome triplication (WGT). In addition, small-scale events such as tandem or segmental duplications and retrotransposition also enable plants to reshape their genomes. Over the decades, extensive research efforts have been undertaken to understand the evolutionary significance of polyploidy. On the other hand, much less attention has been paid to understanding the impact of gene duplication on the diversification of important stress response genes. The main objective of this review is to discuss key aspects of gene and genome duplications with a focus on genes primarily regulated by osmotic stresses. The focal family is the Brassicaceae, since it (i) underwent multiple rounds of WGDs plus WGTs, (ii) hosts many economically important crops and wild relatives that are tolerant to a range of stresses, and (iii) comprises many species that have already been sequenced. Diverse molecular mechanisms that lead to structural and regulatory alterations of duplicated genes are discussed. Examples are drawn from recent literature to elucidate expanded, stress responsive gene families identified from different Brassica crops. A combined bioinformatic and transcriptomic method has been proposed and tested on a known stress-responsive gene pair to prove that stress-responsive duplicated allelic variants can be identified by this method. Finally, future prospects for engineering these genes into crops to enhance stress tolerance are discussed, and important resources for Brassica genome research are provided.

Simultaneous induction of mutant alleles of two allergenic genes in soybean by using site-directed mutagenesis

BACKGROUND

Soybean (Glycine max) is a major protein crop, because soybean protein has an amino acid score comparable to that of beef and egg white. However, many allergens have been identified among soybean proteins. A decrease in allergenic protein levels would be useful for expanding the market for soybean proteins and processed foods. Recently, the CRISPR/Cas9 system has been adopted as a powerful tool for the site-directed mutagenesis in higher plants. This system is expected to generate hypoallergenic soybean varieties.

RESULTS

We used two guide RNAs (gRNAs) and Agrobacterium-mediated transformation for simultaneous site-directed mutagenesis of two genes encoding the major allergens Gly m Bd 28 K and Gly m Bd 30 K in two Japanese soybean varieties, Enrei and Kariyutaka. We obtained two independent T0 Enrei plants and nine T0 Kariyutaka plants. Cleaved amplified polymorphic sequence (CAPS) analysis revealed that mutations were induced in both targeted loci of both soybean varieties. Sequencing analysis showed that deletions were the predominant mutation type in the targeted loci. The Cas9-free plants carrying the mutant alleles of the targeted loci with the transgenes excluded by genetic segregation were obtained in the T2 and T3 generations. Variable mutational spectra were observed in the targeted loci even in T2 and T3 progenies of the same T0 plant. Induction of multiple mutant alleles resulted in six haplotypes in the Cas9-free mutants derived from one T0 plant. Immunoblot analysis revealed that no Gly m Bd 28 K or Gly m Bd 30 K protein accumulated in the seeds of the Cas9-free plants. Whole-genome sequencing confirmed that a Cas9-free mutant had also no the other foreign DNA from the binary vector. Our results demonstrate the applicability of the CRISPR/Cas9 system for the production of hypoallergenic soybean plants.

CONCLUSIONS

Simultaneous site-directed mutagenesis by the CRISPR/Cas9 system removed two major allergenic proteins from mature soybean seeds. This system enables rapid and efficient modification of seed components in soybean varieties.

An efficient virus-induced gene silencing (VIGS) system for functional genomics in Brassicas using a cabbage leaf curl virus (CaLCuV)-based vector

CaLCuV-based VIGS effectively works in cabbage and contributes to efficient functional genomics research in Brassica crop species. Virus-induced gene silencing (VIGS), a posttranscriptional gene silencing method, is an effective technique for analysing the functions of genes in plants. However, no VIGS vectors have been available for Brassica oleracea until now. Here, tobacco rattle virus (TRV), pTYs and cabbage leaf curl virus (CaLCuV) gene-silencing vectors (PCVA/PCVB) were chosen to improve the VIGS system in cabbage using the phytoene desaturase (PDS) gene as an efficient visual indicator of VIGS. We successfully silenced the expression of PDS and observed photobleaching phenomena in cabbage in response to pTYs and CaLCuV, with the latter being more easy to operate and less expensive. The parameters potentially affecting the silencing efficiency of VIGS by CaLCuV in cabbage, including the targeting fragment strategy, inoculation method and incubation temperature, were then compared. The optimized CaLCuV-based VIGS system involves the following: an approximately 500 bp insert sequence, an Agrobacterium OD₆₀₀ of 1.0, use of the vacuum osmosis method applied at the bud stage, and an incubation temperature of 22 °C. Using these parameters, we achieved a stable silencing efficiency of 65%. To further test the effectiveness of the system, we selected the Mg-chelatase H subunit (ChlH) gene in cabbage and knocked down its expression, and we observed yellow leaves, as expected. We successfully applied the CaLCuV-based VIGS system to two other representative Brassica crop species, B. rapa and B. nigra, and thus expanded the application scope of this system. Our VIGS system described here will contribute to efficient functional genomics research in Brassica crop species.

Cloning and functional analysis of three aphid alarm pheromone genes from German chamomile (Matricaria chamomilla L.)

German chamomile (Matricaria chamomilla L.) is one of the most ancient medicinal species in the world and terpenoids from their flowers have important medicinal value. We cloned three sesquiterpene synthase genes, McGDS1, McGDS2 and McGDS3, and performed sequence alignment and phylogenetic analysis. The encoded proteins possess three conserved structural features: an RRxxxxxxxxW motif, an RxR motif, and a DDxxD motif. McGDS1, McGDS2 and McGDS3 were confirmed to be (E)-farnesene synthase, germacrene D synthase, and germacrene A synthase, respectively. Subcellular localization revealed diffuse GFP reporter-gene signals in the cytoplasm and nucleus. qPCR indicated that McGDS1, McGDS2 and McGDS3, were more highly expressed in young flowers than in old flowers and the expression was highly correlated with amounts of the end-product essential oils ((E)-β-farnesene, germacrene D and β-elemene), with coefficients of 0.76, 0.83 and 0.68, respectively. We also established a transformation system for chamomile hairy roots. The overexpression of McGDS1, McGDS2 and McGDS3 resulted in γ-muurolene accumulation in hairy roots. The activity of three aphid alarm pheromones here forms the molecular basis for the study of the biosynthesis and regulation of volatile terpenes. Transformation of chamomile hairy roots provides a simple system in which to study terpene biosynthesis in chamomile.

Hairy Root Cultures-A Versatile Tool With Multiple Applications

Hairy roots derived from the infection of a plant by Rhizobium rhizogenes (previously referred to as Agrobacterium rhizogenes) bacteria, can be obtained from a wide variety of plants and allow the production of highly diverse molecules. Hairy roots are able to produce and secrete complex active glycoproteins from a large spectrum of organisms. They are also adequate to express plant natural biosynthesis pathways required to produce specialized metabolites and can benefit from the new genetic tools available to facilitate an optimized production of tailor-made molecules. This adaptability has positioned hairy root platforms as major biotechnological tools. Researchers and industries have contributed to their advancement, which represents new alternatives from classical systems to produce complex molecules. Now these expression systems are ready to be used by different industries like pharmaceutical, cosmetics, and food sectors due to the development of fully controlled large-scale bioreactors. This review aims to describe the evolution of hairy root generation and culture methods and to highlight the possibilities offered by hairy roots in terms of feasibility and perspectives.

Efficient Generation of CRISPR/Cas9-Mediated Homozygous/Biallelic Medicago truncatula Mutants Using a Hairy Root System

In the process of acquiring mutants mediated by CRISPR/Cas9, plantlets are often regenerated from both mutated and non-mutated cells in a random manner, which increase the odds of chimeric mutated plant. In general, it's necessary to infect more explants or grow to next generation for the need of generating more biallelic or homozygous mutants. In present study, an efficient way of obtaining biallelic or homozygous mutated lines via fast-growing hairy root system without increasing numbers of infected explants or prolonging sexual propagation generation is reported. The fast growing lateral branches of hair roots are originated deep within the parental root from a small number of founder cells at the periphery, and therefore were employed as a library that classify different editing types in different lateral branches in which the homozygous or biallelic lines were screened. Here, MtPDS was employed in a proof-of-concept experiment to evaluate the efficiency of genome editing with our hairy root system. Homozygous/biallelic mutations were found only 1 of the 20 lines in the 1^st generation hairy roots, and 8 lines randomly selected were cultured to obtain their branch roots, homozygous/biallelic mutations were found in 6 of the 8 lines in their branch roots. We also tested the method with MtCOMT gene and got the same result. All of the seedlings regenerated from the homozygous/biallelic hairy root mutation lines of MtPDS displayed albino phenotypes. The entire process from vector design to the recovery of plantlets with homozygous/biallelic mutations took approximately 4.5-6.5 months. The whole process could bring inspiration for efficiently generating homozygous/biallelic mutants through CRISPR/Cas9 system from the hairy root or root system of a chimeric mutated transformants, especially for the rare and endangered plants whose explants sources are very limited or the plants that lack of tissue culture and rapid propagation system.

CRISPR/Cas9 Genome Editing Technology: A Valuable Tool for Understanding Plant Cell Wall Biosynthesis and Function

For the past 5 years, clustered regularly interspaced short palindromic repeats/CRISPR-associated protein 9 (CRISPR/Cas9) technology has appeared in the molecular biology research spotlight. As a game-changing player in genome editing, CRISPR/Cas9 technology has revolutionized animal research, including medical research and human gene therapy as well as plant science research, particularly for crop improvement. One of the most common applications of CRISPR/Cas9 is to generate genetic knock-out mutants. Recently, several multiplex genome editing approaches utilizing CRISPR/Cas9 were developed and applied in various aspects of plant research. Here we summarize these approaches as they relate to plants, particularly with respect to understanding the biosynthesis and function of the plant cell wall. The plant cell wall is a polysaccharide-rich cell structure that is vital to plant cell formation, growth, and development. Humans are heavily dependent on the byproducts of the plant cell wall such as shelter, food, clothes, and fuel. Genes involved in the assembly of the plant cell wall are often highly redundant. To identify these redundant genes, higher-order knock-out mutants need to be generated, which is conventionally done by genetic crossing. Compared with genetic crossing, CRISPR/Cas9 multi-gene targeting can greatly shorten the process of higher-order mutant generation and screening, which is especially useful to characterize cell wall related genes in plant species that require longer growth time. Moreover, CRISPR/Cas9 makes it possible to knock out genes when null T-DNA mutants are not available or are genetically linked. Because of these advantages, CRISPR/Cas9 is becoming an ideal and indispensable tool to perform functional studies in plant cell wall research. In this review, we provide perspectives on how to design CRISPR/Cas9 to achieve efficient gene editing and multi-gene targeting in plants. We also discuss the recent development of the virus-based CRISPR/Cas9 system and the application of CRISPR/Cas9 to knock in genes. Lastly, we summarized current progress on using CRISPR/Cas9 for the characterization of plant cell wall-related genes.

Tissue-specific respiratory burst oxidase homolog-dependent H2O2 signaling to the plasma membrane H+-ATPase confers potassium uptake and salinity tolerance in Cucurbitaceae

Potassium (K+) is a critical determinant of salinity tolerance, and H2O2 has been recognized as an important signaling molecule that mediates many physiological responses. However, the details of how H2O2 signaling regulates K+ uptake in the root under salt stress remain elusive. In this study, salt-sensitive cucumber and salt-tolerant pumpkin which belong to the same family, Cucurbitaceae, were used to answer the above question. We show that higher salt tolerance in pumpkin was related to its superior ability for K+ uptake and higher H2O2 accumulation in the root apex. Transcriptome analysis showed that salinity induced 5816 (3005 up- and 2811 down-) and 4679 (3965 up- and 714 down-) differentially expressed genes (DEGs) in cucumber and pumpkin, respectively. DEGs encoding NADPH oxidase (respiratory burst oxidase homolog D; RBOHD), 14-3-3 protein (GRF12), plasma membrane H+-ATPase (AHA1), and potassium transporter (HAK5) showed higher expression in pumpkin than in cucumber under salinity stress. Treatment with the NADPH oxidase inhibitor diphenylene iodonium resulted in lower RBOHD, GRF12, AHA1, and HAK5 expression, reduced plasma membrane H+-ATPase activity, and lower K+ uptake, leading to a loss of the salinity tolerance trait in pumpkin. The opposite results were obtained when the plants were pre-treated with exogenous H2O2. Knocking out of RBOHD in pumpkin by CRISPR/Cas9 [clustered regularly interspaced short palindromic repeat (CRISPR)/CRISPR-associated protein 9] editing of coding sequences resulted in lower root apex H2O2 and K+ content and GRF12, AHA1, and HAK5 expression, ultimately resulting in a salt-sensitive phenotype. However, ectopic expression of pumpkin RBOHD in Arabidopsis led to the opposite effect. Taken together, this study shows that RBOHD-dependent H2O2 signaling in the root apex is important for pumpkin salt tolerance and suggests a novel mechanism that confers this trait, namely RBOHD-mediated transcriptional and post-translational activation of plasma membrane H+-ATPase operating upstream of HAK5 K+ uptake transporters.

Small-Scale Bioreactor for Sterile Hydroponics and Hairy Roots: Metabolic Diversity and Salicylic Acid Exudation by Hairy Roots of Hyoscyamus niger

The volume and complexity of commercial bioreactors for sterile hydroponics and hairy roots are too large for comparative analysis of many cultures. Here a small-scale bioreactor fabricated from standard glass materials and suitable for both airlift and bubble aeration mode is described. The performance of the bioreactor was tested by growing oilseed rape (Brassica napus L.) and rose plants (Rosa canina L.) in sterile hydroponics and by cultivating hairy roots of henbane (Hyoscyamus niger L.) and sesame (Hyoscyamus niger L.). Plants grown in hydroponics for up to six weeks did not show chloroses or necroses. Hairy roots grew faster or comparably fast in bioreactors as compared to shaking flasks. Root exudates of roses and exudates of hairy roots of henbane were subjected to targeted and nontargeted analysis by HPLC coupled with optical and mass spectrometric detectors. The diversity and concentration of hairy root exudates were higher in bioreactors than in shaking flasks. The composition of hairy root exudates of three accessions of H. niger did not match the genetic relatedness among the accessions. Hairy roots of Hyoscyamus niger exuded salicylic acid in amounts varying among plant accessions and between bioreactors and shaking flask cultures.

Efficient genome editing of Brassica campestris based on the CRISPR/Cas9 system

Conventional methods for gene function study in Brassica campestris have lots of drawbacks, which greatly hinder the identification of important genes' functions and molecular breeding. The clustered, regularly interspaced, short palindromic repeats (CRISPR) and CRISPR-associated protein 9 (CRISPR/Cas9) system is a versatile tool for genome editing that has been widely utilized in many plant species and has many advantages over conventional methods for gene function study. However, the application of CRISPR/Cas9 system in B. campestris remains unreported. The pectin-methylesterase genes Bra003491, Bra007665, and Bra014410 were selected as the targets of the CRISPR/Cas9 system. A single-targeting vector and a multitargeting vector were constructed. Different types of mutations were detected in T₀ generation through Agrobacterium transformation. The mutation rate of the three designed sgRNA seeds varied from 20 to 56%. Although the majority of T₀ mutants were chimeric, four homozygous mutants were identified. Transformation with the multitargeting vector generated one line with a large fragment deletion and one line with mutations in two target genes. Mutations in Bra003491 were stable and inherited by T₁ and T₂ generations. Nine mutants which did not contain T-DNA insertions were also obtained. No mutations were detected in predicted potential off-target sites. Our work demonstrated that CRISPR/Cas9 system is efficient on single and multiplex genome editing without off-targeting in B. campestris and that the mutations are stable and inheritable. Our results may greatly facilitate gene functional studies and the molecular breeding of B. campestris and other plants.

Efficient Genome Editing Using CRISPR/Cas9 Technology in Chicory

CRISPR/Cas9 (Clustered Regularly Interspaced Short Palindromic Repeats/CRISPR associated with protein CAS9) is a genome-editing tool that has been extensively used in the last five years because of its novelty, affordability, and feasibility. This technology has been developed in many plant species for gene function analysis and crop improvement but has never been used in chicory (Cichorium intybus L.). In this study, we successfully applied CRISPR/Cas9-mediated targeted mutagenesis to chicory using Agrobacterium rhizogenes-mediated transformation and protoplast transfection methods. A U6 promoter (CiU6-1p) among eight predicted U6 promoters in chicory was selected to drive sgRNA expression. A binary vector designed to induce targeted mutations in the fifth exon of the chicory phytoene desaturase gene (CiPDS) was then constructed and used to transform chicory. The mutation frequency was 4.5% with the protoplast transient expression system and 31.25% with A. rhizogenes-mediated stable transformation. Biallelic mutations were detected in all the mutant plants. The use of A. rhizogenes-mediated transformation seems preferable as the regeneration of plants is faster and the mutation frequency was shown to be higher. With both transformation methods, foreign DNA was integrated in the plant genome. Hence, selection of vector (transgene)-free segregants is required. Our results showed that genome editing with CRISPR/Cas9 system can be efficiently used with chicory, which should facilitate and accelerate genetic improvement and functional biology.

Genome editing for horticultural crop improvement

Horticultural crops provide humans with many valuable products. The improvement of the yield and quality of horticultural crops has been receiving increasing research attention. Given the development and advantages of genome-editing technologies, research that uses genome editing to improve horticultural crops has substantially increased in recent years. Here, we briefly review the different genome-editing systems used in horticultural research with a focus on clustered regularly interspaced palindromic repeats (CRISPR)/CRISPR-associated 9 (Cas9)-mediated genome editing. We also summarize recent progress in the application of genome editing for horticultural crop improvement. The combination of rapidly advancing genome-editing technology with breeding will greatly increase horticultural crop production and quality.

Creating Targeted Gene Knockouts in Brassica oleracea Using CRISPR/Cas9

While public and political views on genetic modification (inserting "foreign" genes to elicit new traits) have resulted in limited exploitation of the technology in some parts of the world, the new era of genome editing (to edit existing genes to gain new traits/genetic variation) has the potential to change the biotech landscape. Genome editing offers a faster and simpler approach to gene knockout in both single and multiple genetic locations, within a single or small number of generations, in a way that has not been possible through alternative breeding methods. Here we describe an Agrobacterium-mediated delivery approach to deliver Cas9 and dual sgRNAs into 4-day-old cotyledonary petioles of Brassica oleracea. Mutations are detected in approximately 10% of primary transgenic plants and go on in subsequent T1 and T2 generations to segregate away from the T-DNA. This enables the recovery of non-transgenic, genome-edited plants carrying a variety of mutations at the target locus.

Molecular Background of Pi Deficiency-Induced Root Hair Growth in Brassica carinata - A Fasciclin-Like Arabinogalactan Protein Is Involved

Formation of longer root hairs under limiting phosphate (P) conditions can increase the inorganic P (Pi) uptake. Here, regulatory candidate genes for Pi deficiency-induced root hair growth were identified by comparison of massive analysis of cDNA ends (MACE) provided expression profiles of two Brassica carinata cultivars (cv.) differing in their root hair response to Pi deficiency: cv. Bale develops longer root hairs under Pi deficiency, but not cv. Bacho. A split-root experiment was conducted for the differentiation between locally and systemically regulated genes. Furthermore, plants were exposed to nitrogen and potassium deficiency to identify P-specific reacting genes. The latter were knocked out by CRISPR/Cas9 and the effect on the root hair length was determined. About 500 genes were differentially expressed under Pi deficiency in cv. Bale, while these genes did not respond to the low P supply in cv. Bacho. Thirty-three candidate genes with a potential regulatory role were selected and the transcriptional regulation of 30 genes was confirmed by quantitative PCR. Only five candidate genes seemed to be either exclusively regulated locally (two) or systemically (three), whereas 25 genes seemed to be involved in both local and systemic signaling pathways. Potassium deficiency affected neither the root hair length nor the expression of the 30 candidate genes. By contrast, both P and nitrogen deficiency increased the root hair length, and both affected the transcript levels in 26 cases. However, four genes reacted specifically to Pi starvation. These genes and, additionally, INORGANIC PHOSPHATE TRANSPORTER 1 (BcPHT1) were targeted by CRISPR/Cas9. However, even if the transcript levels of five of these genes were clearly decreased, FASCICLIN-LIKE ARABINOGALACTAN PROTEIN 1 (BcFLA1) was the only gene whose downregulation reduced the root hair length in transgenic hairy roots under Pi-deficient conditions. To the best of our knowledge, this is the first study describing a fasciclin-like arabinogalactan protein with a predicted role in the Pi deficiency-induced root hair elongation.

Fascinating Fasciclins: A Surprisingly Widespread Family of Proteins that Mediate Interactions between the Cell Exterior and the Cell Surface

The Fasciclin 1 (FAS1) domain is an ancient structural motif in extracellular proteins present in all kingdoms of life and particularly abundant in plants. The FAS1 domain accommodates multiple interaction surfaces, enabling it to bind different ligands. The frequently observed tandem FAS1 arrangement might both positively and negatively regulate ligand binding. Additional protein domains and post-translational modifications are partially conserved between different evolutionary clades. Human FAS1 family members are associated with multiple aspects of health and disease. At the cellular level, mammalian FAS1 proteins are implicated in extracellular matrix structure, cell to extracellular matrix and cell to cell adhesion, paracrine signaling, intracellular trafficking and endocytosis. Mammalian FAS1 proteins bind to the integrin family of receptors and to protein and carbohydrate components of the extracellular matrix. FAS1 protein encoding plant genes exert effects on cellulosic and non-cellulosic cell wall structure and cellular signaling but to establish the modes of action for any plant FAS1 protein still requires biochemical experimentation. In fungi, eubacteria and archaea, the differential presence of FAS1 proteins in closely related organisms and isolated biochemical data suggest functions in pathogenicity and symbiosis. The inter-kingdom comparison of FAS1 proteins suggests that molecular mechanisms mediating interactions between cells and their environment may have evolved at the earliest known stages of evolution.

Plant Tissue Culture: A Battle Horse in the Genome Editing Using CRISPR/Cas9

Plant tissue culture (PTC) is a set of techniques for culturing cells, tissues, or organs in an aseptic medium with a defined chemical composition, in a controlled environment. Tissue culture, when combined with molecular biology techniques, becomes a powerful tool for the study of metabolic pathways, elucidation of cellular processes, genetic improvement and, through genetic engineering, the generation of cell lines resistant to biotic and abiotic stress, obtaining improved plants of agronomic interest, or studying the complex cellular genome. In this chapter, we analyze in general the use of plant tissue culture, in particular protoplasts and calli, in the implementation of CRISPR/Cas9 technology.

DNA-Free Genome Editing of Brassica oleracea and B. rapa Protoplasts Using CRISPR-Cas9 Ribonucleoprotein Complexes

The CRISPR/Cas9 genome editing system has already proved its efficiency, versatility and simplicity in numerous applications in human, animal, microbe and plant cells. Together with the vast amount of genome and transcriptome databases available, it represents an enormous potential for plant breeding and research. Although most changes produced with CRISPR/Cas9 do not differ from naturally occurring mutations, the use of transgenesis during varietal development can still trigger GMO legislation in countries that rely on process-based regulation. Moreover, stable integration of DNA coding for genome-editing tools into plant genomes can result in insertional mutagenesis, while its prolonged expression can cause mutations in off-target sites. These pitfalls can be avoided with the delivery of preassembled ribonucleoprotein complexes (RNPs) composed of purified recombinant enzyme Cas9 and in vitro-transcribed or synthesized sgRNA. We therefore aimed to develop a DNA-free protocol for site-directed mutagenesis of three species of the genus Brassica (B. oleracea, B. napus, and B. rapa) with the use of RNPs. We chose cabbage, rapeseed and Chinese cabbage as species representatives and introduced RNPs into their protoplasts with PEG 4000. Four sgRNAs targeting two endogenous genes (the FRI and PDS genes, two sgRNAs per gene) were introduced into all three species. No mutations were detected after transfection of rapeseed protoplasts, while we obtained mutation frequencies of 0.09 to 2.25% and 1.15 to 24.51% in cabbage and Chinese cabbage, respectively. In both species, a positive correlation was displayed between the amount (7.5, 15, 30, and 60 μg) of Cas9 enzyme and sgRNA introduced and mutation frequency. Nucleotide changes (insertions and deletions) were detected 24 h after transfection and did not differ 72 h after transfection. They were species-, gene- and locus-dependent. In summary, we demonstrated the suitability of RNP transfection into B. oleracea and B. rapa protoplasts for high-efficiency indel induction of two endogenous genes. Due to the relatively high mutation frequencies detected (up to 24.51%), this study paves the way for regeneration of precisely mutated Brassica plants without the use of transgenesis.