An efficient Agrobacterium-mediated soybean transformation method using green fluorescent protein as a selectable marker

Utility of Arabidopsis KASII Promoter in Development of an Effective CRISPR/Cas9 System for Soybean Genome Editing and Its Application in Engineering of Soybean Seeds Producing Super-High Oleic and Low Saturated Oils

This study reports the use of the Arabidopsis KASII promoter (AtKASII) to develop an efficient CRISPR/Cas9 system for soybean genome editing. When this promoter was paired with Arabidopsis U6 promoters to drive Cas9 and single guide RNA expression, respectively, simultaneous editing of the three fatty acid desaturase genes GmFAD2-1A, GmFAD2-1B, and GmFAD3A occurred in more than 60% of transgenic soybean lines at T2 generation, and all the triple mutants possessed desirable high-oleic traits. In sharp contrast, not a single line underwent simultaneous editing of the three target genes when AtKASII was replaced by the widely used AtEC1.2 promoter. Furthermore, our study showed that the stable and inheritable mutations in the high-oleic lines did not alter the overall contents of oil and protein or amino acid composition while increasing the oleic acid content up to 87.6% from approximately 23.8% for wild-type seeds, concomitant with 34.4- and 3.7-fold reductions in linoleic and linolenic acid, respectively. Collectively, this study demonstrates that the AtKASII promoter is highly promising for optimization of the CRISPR/Cas9 system for genome editing in soybean and possibly beyond.

Recalcitrance to transformation, a hindrance for genome editing of legumes

Plant genome editing, a recently discovered method for targeted mutagenesis, has emerged as a promising tool for crop improvement and gene function research. Many genome-edited plants, such as rice, wheat, and tomato, have emerged over the last decade. As the preliminary steps in the procedure for genome editing involve genetic transformation, amenability to genome editing depends on the efficiency of genetic engineering. Hence, there are numerous reports on the aforementioned crops because they are transformed with relative ease. Legume crops are rich in protein and, thus, are a favored source of plant proteins for the human diet in most countries. However, legume cultivation often succumbs to various biotic/abiotic threats, thereby leading to high yield loss. Furthermore, certain legumes like peanuts possess allergens, and these need to be eliminated as these deprive many people from gaining the benefits of such crops. Further genetic variations are limited in certain legumes. Genome editing has the potential to offer solutions to not only combat biotic/abiotic stress but also generate desirable knock-outs and genetic variants. However, excluding soybean, alfalfa, and Lotus japonicus, reports obtained on genome editing of other legume crops are less. This is because, excluding the aforementioned three legume crops, the transformation efficiency of most legumes is found to be very low. Obtaining a higher number of genome-edited events is desirable as it offers the option to genotypically/phenotypically select the best candidate, without the baggage of off-target mutations. Eliminating the barriers to genetic engineering would directly help in increasing genome-editing rates. Thus, this review aims to compare various legumes for their transformation, editing, and regeneration efficiencies and discusses various solutions available for increasing transformation and genome-editing rates in legumes.

Functional Analysis of Pheromone Biosynthesis Activating Neuropeptide Receptor Isoforms in Maruca vitrata

Insect sex pheromones are volatile chemicals that induce mating behavior between conspecific individuals. In moths, sex pheromone biosynthesis is initiated when pheromone biosynthesis-activating neuropeptide (PBAN) synthesized in the suboesophageal ganglion binds to its receptor on the epithelial cell membrane of the pheromone gland. To investigate the function of PBAN receptor (PBANR), we identified two PBANR isoforms, MviPBANR-B and MviPBANR-C, in the pheromone glands of Maruca vitrata. These two genes belong to G protein-coupled receptors (GPCRs) and have differences in the C-terminus but share a 7-transmembrane region and GPCR family 1 signature. These isoforms were expressed in all developmental stages and adult tissues. MviPBANR-C had the highest expression level in pheromone glands among the examined tissues. Through in vitro heterologous expression in HeLa cell lines, only MviPBANR-C-transfected cells responded to MviPBAN (≥5 µM MviPBAN), inducing Ca²⁺ influx. Sex pheromone production and mating behavior were investigated using gas chromatography and a bioassay after MviPBANR-C suppression by RNA interference, which resulted in the major sex pheromone component, E10E12-16:Ald, being quantitatively reduced compared to the control, thereby decreasing the mating rate. Our findings indicate that MviPBANR-C is involved in the signal transduction of sex pheromone biosynthesis in M. vitrata and that the C-terminal tail plays an important role in its function.

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

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

Suppression of pheromone biosynthesis and mating behavior by RNA interference of pheromone gland-specific fatty acyl reductase in Maruca vitrata

In moths, various enzymes, such as fatty acid synthases, fatty acyl desaturases, and fatty acyl reductases (FARs), are involved in pheromone biosynthesis. In particular, pheromone gland-specific FAR (pgFAR) plays an important role in converting the functional group from carboxylic to alcohol during pheromone biosynthesis. A novel pgFAR of Maruca vitrata, Mvi-pgFAR, was identified through transcriptome sequencing of its pheromone gland. To investigate the involvement of Mvi-pgFAR in pheromone biosynthesis, Mvi-pgFAR was cloned from the pheromone gland and suppressed by RNA interference (RNAi). Mvi-pgFAR harbored several conserved motifs related to NAD(P)H-binding, N-glycosylation, and adenosine / guanosine triphosphate binding. Phylogenetic analysis revealed that Mvi-pgFAR with other lepidopteran pgFARs formed an independent clade. Mvi-pgFAR was specifically expressed only in the pheromone gland. Quantitative real-time polymerase chain reaction showed that the diurnal expression levels of Mvi-pgFAR in the pheromone gland were the highest at 2 h before the scotophase. After primarily confirming Mvi-pgFAR suppression by RNAi, (E,E)-10,12-hexadecadienal (E10E12-16:Ald), a major sex pheromone component, was quantified by gas chromatography. When Mvi-pgFAR was successfully suppressed, E10E12-16:Ald production was reduced by up to half of that of the control, and the mating rate was subsequently decreased. Our results demonstrate that Mvi-pgFAR downregulation can suppress mating behavior by changing the relative sex pheromone component ratio, suggesting that Mvi-pgFAR can be used as a novel control target.

Progress in Soybean Genetic Transformation Over the Last Decade

Soybean is one of the important food, feed, and biofuel crops in the world. Soybean genome modification by genetic transformation has been carried out for trait improvement for more than 4 decades. However, compared to other major crops such as rice, soybean is still recalcitrant to genetic transformation, and transgenic soybean production has been hampered by limitations such as low transformation efficiency and genotype specificity, and prolonged and tedious protocols. The primary goal in soybean transformation over the last decade is to achieve high efficiency and genotype flexibility. Soybean transformation has been improved by modifying tissue culture conditions such as selection of explant types, adjustment of culture medium components and choice of selection reagents, as well as better understanding the transformation mechanisms of specific approaches such as Agrobacterium infection. Transgenesis-based breeding of soybean varieties with new traits is now possible by development of improved protocols. In this review, we summarize the developments in soybean genetic transformation to date, especially focusing on the progress made using Agrobacterium-mediated methods and biolistic methods over the past decade. We also discuss current challenges and future directions.

Current progress and challenges in crop genetic transformation

Plant transformation remains the most sought-after technology for functional genomics and crop genetic improvement, especially for introducing specific new traits and to modify or recombine already existing traits. Along with many other agricultural technologies, the global production of genetically engineered crops has steadily grown since they were first introduced 25 years ago. Since the first transfer of DNA into plant cells using Agrobacterium tumefaciens, different transformation methods have enabled rapid advances in molecular breeding approaches to bring crop varieties with novel traits to the market that would be difficult or not possible to achieve with conventional breeding methods. Today, transformation to produce genetically engineered crops is the fastest and most widely adopted technology in agriculture. The rapidly increasing number of sequenced plant genomes and information from functional genomics data to understand gene function, together with novel gene cloning and tissue culture methods, is further accelerating crop improvement and trait development. These advances are welcome and needed to make crops more resilient to climate change and to secure their yield for feeding the increasing human population. Despite the success, transformation remains a bottleneck because many plant species and crop genotypes are recalcitrant to established tissue culture and regeneration conditions, or they show poor transformability. Improvements are possible using morphogenetic transcriptional regulators, but their broader applicability remains to be tested. Advances in genome editing techniques and direct, non-tissue culture-based transformation methods offer alternative approaches to enhance varietal development in other recalcitrant crops. Here, we review recent developments in plant transformation and regeneration, and discuss opportunities for new breeding technologies in agriculture.

Plant Biosystems Design Research Roadmap 1.0

Human life intimately depends on plants for food, biomaterials, health, energy, and a sustainable environment. Various plants have been genetically improved mostly through breeding, along with limited modification via genetic engineering, yet they are still not able to meet the ever-increasing needs, in terms of both quantity and quality, resulting from the rapid increase in world population and expected standards of living. A step change that may address these challenges would be to expand the potential of plants using biosystems design approaches. This represents a shift in plant science research from relatively simple trial-and-error approaches to innovative strategies based on predictive models of biological systems. Plant biosystems design seeks to accelerate plant genetic improvement using genome editing and genetic circuit engineering or create novel plant systems through de novo synthesis of plant genomes. From this perspective, we present a comprehensive roadmap of plant biosystems design covering theories, principles, and technical methods, along with potential applications in basic and applied plant biology research. We highlight current challenges, future opportunities, and research priorities, along with a framework for international collaboration, towards rapid advancement of this emerging interdisciplinary area of research. Finally, we discuss the importance of social responsibility in utilizing plant biosystems design and suggest strategies for improving public perception, trust, and acceptance.

Removal of gaseous tetrahydrofuran via a three-phase airlift bioreactor loaded with immobilized cells of GFP-tagged Pseudomonas oleovorans GDT4

Tetrahydrofuran (THF) is a common highly toxic cyclic aliphatic ether that frequently exists in waste gases. Removal of gaseous THF is a serious issue with important environmental ramifications. A novel three-phase airlift bioreactor (TPAB) loaded with immobilized cells was developed for efficient THF removal from gas streams. An effective THF-degrading transformant, Pseudomonas oleovorans GDT4, which contains the pTn-Mod-OTc-gfp plasmid and was tagged with a green fluorescent protein (GFP), was constructed. Continuous treatment of THF-containing waste gases was succeeded by the GFP-labelled cells immobilized with calcium alginate and activated carbon fiber in the TPAB for 60 days with >90% removal efficiency. The number of fluorescent cells in the beads reached 1.7 × 10¹¹ cells·g^-1 of bead on day 10, accounting for 83.3% of the total number of cells. The amount further increased to 3.0 × 10¹¹ cells·g^-1 of bead on day 40. However, it decreased to 2.5 × 10¹¹ cells·g^-1 of bead with a substantial increase in biomass in the liquid because of cell leakage and hydraulic shock. PCR-DGGE revealed that P. oleovorans was the dominant microorganism throughout the entire operation. The maximum elimination capacity was affected by empty bed residence time (EBRT). The capacity was only 25.9 g m^-3·h^-1 at EBRT of 80 s, whereas it reached 37.8 g m^-3·h^-1 at EBRT of 140 s. This work provides an alternative method for full-scale removal of gaseous THF and presents a useful tool for determining the biomass of a specific degrader in immobilized beads.

Anthocyanin, a novel and user-friendly reporter for convenient, non-destructive, low cost, directly visual selection of transgenic hairy roots in the study of rhizobia-legume symbiosis

BACKGROUND

Agrobacterium rhizogenes-mediated hairy root transformation provides a powerful tool for investigating the functions of plant genes involved in rhizobia-legume symbiosis. However, in the traditional identification methods of transgenic hairy roots based on reporter genes, an expensive chemical substrate or equipment is required.

RESULTS

Here, we report a novel, low cost, and robust reporter for convenient, non-destructive, and directly visual selection of transgenic hairy roots by naked eye, which can be used in the study of rhizobia-legume symbiosis. The reporter gene AtMyb75 in Arabidopsis, encoding an R2R3 type MYB transcription factor, was ectopically expressed in hairy roots-mediated by A. rhizogenes, which induced purple/red colored anthocyanin accumulation in crop species like soybean (Glycine max (L.) Merr.) and two model legume species, Lotus japonicas and Medicago truncatula. Transgenic hairy roots of legumes containing anthocyanin can establish effective symbiosis with rhizobia. We also demonstrated the reliability of AtMyb75 as a reporter gene by CRISPR/Cas9-targeted mutagenesis of the soybean resistance to nodulation Rfg1 gene in the soybean PI377578 (Nod-) inoculated with Sinorhizobium fredii USDA193. Without exception, mature nitrogen-fixation nodules, were formed on purple transgenic hairy roots containing anthocyanin.

CONCLUSIONS

Anthocyanin is a reliable, user-friendly, convenient, non-destructive, low cost, directly visual reporter for studying symbiotic nitrogen-fixing nodule development and could be widely applied in broad leguminous plants.