Genetically Transformed Cotton (Gossypium Hirsutum L.) Plants

Founder transformants of cotton (Gossypium hirsutum L.) obtained through the introduction of DS-Red, Rec, Rep and CRISPR/Cas9 expressing constructs for developing base lines of recombinase mediated gene stacking

Cotton being the major fiber crop across the world is exposed to numerous biotic and abiotic stresses. Genetic transformation of cotton is vital to meet the world’s food, feed and fiber demands. Genetic manipulation by randomly transferring the genes emanate variable gene expression. Targeted gene insertion by latest genome editing tools results in predictable expression of genes at a specified location. Gene stacking technology emerged as an adaptive strategy to combat biotic and abiotic stresses by integrating 2–3 genes simultaneously and at a specific site to avoid variable gene expression at diverse locations. This study explains the development of cotton’s founder transformants to be used as a base line for multiple gene stacking projects. We introduced Cre and PhiC31 mediated recombination sites to specify the locus of incoming genes. CRISPR-Cas9 gene was integrated for developing CRISPR based founder lines of cotton. Cas9 gene along with gRNA was integrated to target Rep (replication) region of cotton leaf curl virus. Replication region of virus was specifically targeted to diminish further proliferation and preventing the virus to develop new strains. To successfully develop these primary transformants, a model transformation system has been optimized with the red color visualization (DS-Red). Following red color transformation system, three baselines with recombination specified site (Rec), targeted replication region (Rep) and Cas9 founder lines have been developed. These founder transformants are useful for developing recombinase mediated and CRISPR/Cas9 based originator lines of cotton. Moreover, these transformants will set up a base system for all the recombinase mediated gene stacking projects.

Quantifying the Contribution of Seed Blended Refugia in Field Corn to Helicoverpa zea (Lepidoptera: Noctuidae) Populations

Helicoverpa zea (Boddie), a pest of cotton that also occurs in field corn, is commonly controlled through the use of foliar-applied insecticides or transgenic crops expressing Bacillus thuringiensis (Berliner) (Bt) genes. To minimize the risk of Bt resistance in pest populations, refuge systems have been implemented for sustainable agroecosystem management. Historically, structured refuge compliance among growers has been low, leading to the commercialization of seed blended refugia. To test the viability of seed blended refugia in southern U.S. field corn, field studies were conducted in Mississippi and Georgia during 2016, 2017, and 2018 growing seasons. To quantify adult H. zea emergence from structured (non-Bt corn) and seed blended refuge options, emergence traps were utilized. Kernel damage among seed blended refuge and structured refuge corn ears were recorded and compared. The timing of moth emergence was recorded. When compared to a structured refuge, H. zea adult moth emergence from seed blended refugia did not significantly differ. Kernel damage of non-Bt plants in the seed blended treatments was not significantly different than non-Bt plants in the structured refuge treatments. Moth emergence timing was not significantly delayed between the structured refuge and seed blended refuge treatments. Results of this study suggest that a seed blended refuge may provide an effective insecticide resistance management alternative for H. zea in areas where structured refuge compliance is low.

Improved cotton transformation protocol mediated by Agrobacterium and biolistic combined-methods

The combined Agrobacterium- and biolistic-mediated methods of cotton transformation provide a straightforward and highly efficient protocol for obtaining transgenic cotton. Cotton (Gossypium spp.) is the most important crop for natural textile fiber production worldwide. Nonetheless, one of the main challenges in cotton production are the losses resulting from insect pests, pathogens, and abiotic stresses. One effective way to solve these issues is to use genetically modified (GM) varieties. Herein, we describe an improved protocol for straightforward and cost-effective genetic transformation of cotton embryo axes, merging biolistics and Agrobacterium. The experimental steps include (1) Agrobacterium preparation, (2) seed sterilization, (3) cotton embryo excision, (4) lesion of shoot-cells by tungsten bombardment, (5) Agrobacterium-mediated transformation, (6) embryo co-culture, (7) regeneration and selection of transgenic plants in vitro, and (8) molecular characterization of plants. Due to the high regenerative power of the embryonic axis and the exceptional ability of the meristem cells for plant regeneration through organogenesis in vitro, this protocol can be performed in approximately 4-10 weeks, with an average plant regeneration of about 5.5% (± 0.53) and final average transformation efficiency of 60% (± 0.55). The transgene was stably inherited, and most transgenic plants hold a single copy of the transgene, as desirable and expected in Agrobacterium-mediated transformation. Additionally, the transgene was stably expressed over generations, and transgenic proteins could be detected at high levels in the T₂ generation of GM cotton plants. The T₂ progeny showed no phenotypic or productivity disparity compared to wild-type plants. Collectively, the use of cotton embryo axes and the enhanced DNA-delivery system by combining particle bombardment and Agrobacterium infection enabled efficient transgenic plant recovery, overcoming usual limitations associated with the recalcitrance of several cotton genotypes subjected to somatic embryogenesis. The improved approach states this method's success for cotton genetic modification, allowing us to obtain GM cotton plants carrying traits, which are of fundamental relevance for the advancement of global agribusiness.

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.

Application of Upstream Open Reading Frames (uORFs) Editing for the Development of Stress-Tolerant Crops

Global population growth and climate change are posing increasing challenges to the production of a stable crop supply using current agricultural practices. The generation of genetically modified (GM) crops has contributed to improving crop stress tolerance and productivity; however, many regulations are still in place that limit their commercialization. Recently, alternative biotechnology-based strategies, such as gene-edited (GE) crops, have been in the spotlight. Gene-editing technology, based on the clustered regularly interspaced short palindromic repeats (CRISPR) platform, has emerged as a revolutionary tool for targeted gene mutation, and has received attention as a game changer in the global biotechnology market. Here, we briefly introduce the concept of upstream open reading frames (uORFs) editing, which allows for control of the translation of downstream ORFs, and outline the potential for enhancing target gene expression by mutating uORFs. We discuss the current status of developing stress-tolerant crops, and discuss uORF targets associated with salt stress-responsive genes in rice that have already been verified by transgenic research. Finally, we overview the strategy for developing GE crops using uORF editing via the CRISPR-Cas9 system. A case is therefore made that the mutation of uORFs represents an efficient method for developing GE crops and an expansion of the scope of application of genome editing technology.

A Stable Agrobacterium rhizogenes-Mediated Transformation of Cotton (Gossypium hirsutum L.) and Plant Regeneration From Transformed Hairy Root via Embryogenesis

Genetic transformation is a powerful tool to study gene function, secondary metabolism pathways, and molecular breeding in crops. Cotton (Gossypium hirsutum L.) is one of the most important economic crops in the world. Current cotton transformation methods take at least seven to culture and are labor-intensive and limited to some cultivars. In this study, we first time achieved plantlet regeneration of cotton via embryogenesis from transformed hairy roots. We inoculated the cotyledon explants of a commercial cultivar Zhongmian-24 with Agrobacterium rhizogenes strain AR1193, harboring a binary vector pBI-35S::GFP that contained the NPT II (neomycin phosphotransferase) gene and the GFP (green fluorescent protein) gene as a fluorescent marker in the T-DNA region. 82.6% explants produced adventitious roots, of which 53% showed GFP expression after transformation. 82% of transformed hairy roots produced embryonic calli, 12% of which regenerated into stable transformed cotton plants after 7 months of culture. The integration of GFP in the transformed cotton genomes were confirmed by PCR (Polymerase chain reaction) and Southern blot analysis as well as the stable expression of GFP were also detected by semi-quantitative RT-PCR analysis. The resultant transformed plantlets were phenotypically, thus avoiding Ri syndrome. Here we report a stable and reproducible method for A. rhizogenes-mediated transformation of cotton using cotyledon as explants, which provides a useful and reliable platform for gene function analysis of cotton.

Direct Germline Transformation of Cotton Meristem Explants With No Selection

Regeneration of transgenic plants without selectable markers can facilitate the development and commercialization of trait stacking products. A wide range of strategies have been developed to eliminate selectable markers to produce marker-free transgenic plants. The most widely used marker free approach is probably the Agrobacterium-based 2 T-DNA strategy where the gene-of-interest (GOI) and selectable marker gene are delivered from independent T-DNAs (Darbani et al., 2007). The selectable marker gene is segregated away from the GOI in subsequent generations. However, the efficiency of this 2 T-DNA system is much less than the traditional 1 T-DNA system due to the inefficiency of T-DNA co-transformation and high rate of con-integration between the GOI and selectable marker gene T-DNAs. In contrast, no selection transformation utilizes a single T-DNA carrying the GOI and thus eliminates the need to remove the selectable marker insert and potentially provides a viable alternative marker-free system. In this study, we reported the successful regeneration of transgenic cotton plants through Agrobacterium inoculation of seed meristem explants without the use of selective agents. Regeneration of putative transgenic plants were identified by GUS histo-chemical assay. The germline transmission of transgene to progeny was determined by segregation of pollen grains, immature embryos and T1 plants by GUS expression. The results were further confirmed by Southern analyses. The marker-free transformation frequency in this no selection system was similar to current meristem transformation system with selection (0.2%-0.7%). The strategy for further improvement of this system and its implication in improving cotton transformation pipeline and in developing transgene-free genome editing technology is discussed.

Phalaenopsis LEAFY COTYLEDON1-Induced Somatic Embryonic Structures Are Morphologically Distinct From Protocorm-Like Bodies

Somatic embryogenesis is commonly used for clonal propagation of a wide variety of plant species. Induction of protocorm-like-bodies (PLBs), which are capable of developing into individual plants, is a routine tissue culture-based practice for micropropagation of orchid plants. Even though PLBs are often regarded as somatic embryos, our recent study provides molecular evidence to argue that PLBs are not derived from somatic embryogenesis. Here, we report and characterize the somatic embryonic tissues induced by Phalaenopsis aphrodite LEAFY COTYLEDON1 (PaLEC1) in Phalaenopsis equestris. We found that PaLEC1-induced somatic tissues are morphologically different from PLBs, supporting our molecular study that PLBs are not of somatic embryonic origin. The embryonic identity of PaLEC1-induced embryonic tissues was confirmed by expression of the embryonic-specific transcription factors FUSCA3 (FUS3) and ABSCISIC ACID INSENSITIVE3 (ABI3), and seed storage proteins 7S GLOBULIN and OLEOSIN. Moreover, PaLEC1-GFP protein was found to be associated with the Pa7S-1 and PaFUS3 promoters containing the CCAAT element, supporting that PaLEC1 directly regulates embryo-specific processes to activate the somatic embryonic program in P. equestris. Despite diverse embryonic structures, PaLEC1-GFP-induced embryonic structures are pluripotent and capable of generating new shoots. Our study resolves the long-term debate on the developmental identity of PLB and suggests that somatic embryogenesis may be a useful approach to clonally propagate orchid seedlings.

Agrobacterium-Mediated Genetic Transformation of Cotton

There are many methods and techniques that can be used to transfer foreign genes into cells. In plant biotechnology, Agrobacterium-mediated transformation is a widely used traditional method for inserting foreign genes into plant genome and obtaining transgenic plants, particularly for dicot plant species. Agrobacterium-mediated transformation of cotton involves several important and also critical steps, which includes co-culture of cotton explants with Agrobacterium, induction and selection of stable transgenic cell lines, recovery of plants from transgenic cells majorly through somatic embryogenesis, and detection and expression analysis of transgenic plants. In this chapter, we describe a detailed step-by-step protocol for obtaining transgenic cotton plants via Agrobacterium-mediated transformation.

The RNase YbeY Is Vital for Ribosome Maturation, Stress Resistance, and Virulence of the Natural Genetic Engineer Agrobacterium tumefaciens

Riboregulation involving regulatory RNAs, RNA chaperones, and ribonucleases is fundamental for the rapid adaptation of gene expression to changing environmental conditions. The gene coding for the RNase YbeY belongs to the minimal prokaryotic genome set and has a profound impact on physiology in a wide range of bacteria. Here, we show that the Agrobacterium tumefaciens ybeY gene is not essential. Deletion of the gene in the plant pathogen reduced growth, motility, and stress tolerance. Most interestingly, YbeY is crucial for A. tumefaciens-mediated T-DNA transfer and tumor formation. Comparative proteomics by using isobaric tags for relative and absolute quantitation (iTRAQ) revealed dysregulation of 59 proteins, many of which have previously been found to be dependent on the RNA chaperone Hfq. YbeY and Hfq have opposing effects on production of these proteins. Accumulation of a 16S rRNA precursor in the ybeY mutant suggests that A. tumefaciens YbeY is involved in rRNA processing. RNA coimmunoprecipitation-sequencing (RIP-Seq) showed binding of YbeY to the region immediately upstream of the 16S rRNA. Purified YbeY is an oligomer with RNase activity. It does not physically interact with Hfq and thus plays a partially overlapping but distinct role in the riboregulatory network of the plant pathogen.IMPORTANCE Although ybeY gene belongs to the universal bacterial core genome, its biological function is incompletely understood. Here, we show that YbeY is critical for fitness and host-microbe interaction in the plant pathogen Agrobacterium tumefaciens Consistent with the reported endoribonuclease activity of YbeY, A. tumefaciens YbeY acts as a RNase involved in maturation of 16S rRNA. This report adds a worldwide plant pathogen and natural genetic engineer of plants to the growing list of bacteria that require the conserved YbeY protein for host-microbe interaction.

Development of Virus Resistance Transgenic Cotton Using Cotton Leaf Curl Virus Antisense ßC1 Gene

Cotton (Gossypium hirsutum L.) is the most economically important crop in the world and produced 90% of the total natural cellulose fiber which is utilized to make cotton fabrics. The production of cotton is affected by many several diseases, and among them, viral disease, especially leaf curl, is the most destructive disease caused by a begomovirus transmitted by whiteflies vector. Plant biotechnology has provided an opportunity to develop transgenic plant with variable traits against biotic and abiotic stress such as resistance against pathogens, yield, quality, and salinity. Transgenic cotton (Gossypium hirsutum L., cv. Coker 312) plants were raised against leaf curl disease using bC1 gene in antisense orientation through Agrobacterium-mediated transformation somatic embryogenesis system. In this chapter, a standardized protocol will be given to raise virus resistance transgenic cotton.

Transgenic Cotton: From Biotransformation Methods to Agricultural Application

Transgenic cotton is among the first transgenic plants commercially adopted around the world. Since it was first introduced into the field in the middle of the 1990s, transgenic cotton has been quickly adopted by cotton farmers in many developed and developing countries. Transgenic cotton has offered many important environmental, social, and economic benefits, including reduced usage of pesticides, indirect increase of yield, minimizing environmental pollution, and reducing labor and cost. Agrobacterium-mediated genetic transformation method is the major method for obtaining transgenic cotton. However, pollen tube pathway-mediated method is also used, particularly by scientists in China, to breed commercial transgenic cotton. Although transgenic cotton plants with disease resistance, abiotic stress tolerance, and improved fiber quality have been developed in the past decades, insect-resistant and herbicide-tolerant cottons are the two dominant cottons in transgenic cotton market.

Gbvdr6, a Gene Encoding a Receptor-Like Protein of Cotton (Gossypium barbadense), Confers Resistance to Verticillium Wilt in Arabidopsis and Upland Cotton

Verticillium wilt is a soil-borne disease that can cause devastating losses in cotton production. Because there is no effective chemical means to combat the disease, the only effective way to control Verticillium wilt is through genetic improvement. Therefore, the identification of additional disease-resistance genes will benefit efforts toward the genetic improvement of cotton resistance to Verticillium wilt. Based on screening of a BAC library with a partial Ve homologous fragment and expression analysis, a V. dahliae-induced gene, Gbvdr6, was isolated and cloned from the Verticillium wilt-resistant cotton G. barbadense cultivar Hai7124. The gene was located in the gene cluster containing Gbve1 and Gbvdr5 and adjacent to the Verticillium wilt-resistance QTL hotspot. Gbvdr6 was induced by Verticillium dahliae Kleb and by the plant hormones salicylic acid (SA), methyl jasmonate (MeJA) and ethephon (ETH) but not by abscisic acid (ABA). Gbvdr6 was localized to the plasma membrane. Overexpression of Gbvdr6 in Arabidopsis and cotton enhanced resistance to V. dahliae. Moreover, the JA/ET signaling pathway-related genes PR3, PDF 1.2, ERF1 and the SA-related genes PR1 and PR2 were constitutively expressed in transgenic plants. Gbvdr6-overexpressing Arabidopsis was less sensitive than the wild-type plant to MeJA. Furthermore, the accumulation of reactive oxygen species and callose was triggered at early time points after V. dahliae infection. These results suggest that Gbvdr6 confers resistance to V. dahliae through regulation of the JA/ET and SA signaling pathways.

A transient transformation system for gene characterization in upland cotton (Gossypium hirsutum)

BACKGROUND

Genetically modified cotton accounts for 64% of the world's cotton growing area (22.3 million hectares). The genome sequencing of the diploid cotton progenitors Gossypium raimondii and Gossypium arboreum as well as the cultivated Gossypium hirsutum has provided a wealth of genetic information that could be exploited for crop improvement. Unfortunately, gene functional characterization in cotton is lagging behind other economically important crops due to the low efficiency, lengthiness and technical complexity of the available stable transformation methods. We present here a simple, fast and efficient method for the transient transformation of G. hirsutum that can be used for gene characterization studies.

RESULTS

We developed a transient transformation system for gene characterization in upland cotton. Using β-glucuronidase as a reporter for Agrobacterium-mediated transformation assays, we evaluated multiple transformation parameters such as Agrobacterium strain, bacterial density, length of co-cultivation, chemicals and surfactants, which can affect transformation efficiency. After the initial characterization, the Agrobacterium EHA105 strain was selected and a number of binary constructs used to perform gene characterization studies. 7-days-old cotton seedlings were co-cultivated with Agrobacterium and transient gene expression was observed 5 days after infection of the plants. Transcript levels of two different transgenes under the control of the cauliflower mosaic virus (CaMV) 35S promoter were quantified by real-time reverse transcription PCR (qRT-PCR) showing a 3-10 times increase over the levels observed in non-infected controls. The expression patterns driven by the promoters of two G. hirsutum genes as well as the subcellular localization of their corresponding proteins were studied using the new transient expression system and our observations were consistent with previously published results using Arabidopsis as a heterologous system.

CONCLUSIONS

The Agrobacterium-mediated transient transformation method is a fast and easy transient expression system enabling high transient expression and transformation efficiency in upland cotton seedlings. Our method can be used for gene functional studies such as promoter characterization and protein subcellular localization in cotton, obviating the need to perform such studies in a heterologous system such as Arabidopsis.

ABP9, a maize bZIP transcription factor, enhances tolerance to salt and drought in transgenic cotton

ABP9 , encoding a bZIP transcription factor from maize, enhances tolerance to multiple stresses and may participate in the ABA signaling pathway in transgenic cotton by altering physiological and biochemical processes and stress-related gene expression. Abiotic stresses, such as soil salinity and drought, negatively affect growth, development, and yield in cotton. Gene ABP9, which encodes a bZIP transcription factor, binds to the abscisic acid (ABA)-responsive-element (ABRE2) motif of the maize catalase1 gene. Its expression significantly improves tolerance in Arabidopsis to multiple abiotic stresses, but little is known about its role in cotton. In the present study, the ABP9 gene was introduced into upland cotton (Gossypium hirsutum L.) cultivar R15 by Agrobacterium tumefaciens-mediated transformation, and 12 independent transgenic cotton lines were obtained. Cotton plants over-expressing ABP9 have enhanced tolerance to salt and osmotic stress. Under stress, they developed better root systems in a greenhouse and higher germination, reduced stomatal aperture, and stomatal density in a growth chamber. Under drought conditions, survival rate and relative water content (RWC) of transgenic cotton were higher than those of R15 plants. Under salt and osmotic stresses, chlorophyll, proline, and soluble sugar contents significantly increased in transgenic cotton leaves and the malondialdehyde (MDA) content was lower than in R15. Overexpression of ABP9 also enhanced oxidative stress tolerance, reduced cellular levels of reactive oxygen species (ROS) through increased activities of antioxidative enzymes, and alleviated oxidative damage to cell. Interestingly, ABP9 over-expressing cotton was more sensitive to exogenous ABA than R15 at seed germination, root growth, stomatal aperture, and stomatal density. Moreover, ABP9 overexpression upregulated significantly the transcription levels of stress-related genes such as GhDBP2, GhNCED2, GhZFP1, GhERF1, GhHB1, and GhSAP1 under salt treatment. Conjointly, these results showed that overexpression of ABP9 conferred enhanced tolerance to multiple abiotic stresses in cotton. The stress-tolerant transgenic lines provide valuable resources for cotton breeding.

Transgenic Cotton Plants Expressing Cry1Ia12 Toxin Confer Resistance to Fall Armyworm (Spodoptera frugiperda) and Cotton Boll Weevil (Anthonomus grandis)

Gossypium hirsutum (commercial cooton) is one of the most economically important fibers sources and a commodity crop highly affected by insect pests and pathogens. Several transgenic approaches have been developed to improve cotton resistance to insect pests, through the transgenic expression of different factors, including Cry toxins, proteinase inhibitors, and toxic peptides, among others. In the present study, we developed transgenic cotton plants by fertilized floral buds injection (through the pollen-tube pathway technique) using an DNA expression cassette harboring the cry1Ia12 gene, driven by CaMV35S promoter. The T0 transgenic cotton plants were initially selected with kanamycin and posteriorly characterized by PCR and Southern blot experiments to confirm the genetic transformation. Western blot and ELISA assays indicated the transgenic cotton plants with higher Cry1Ia12 protein expression levels to be further tested in the control of two major G. hirsutum insect pests. Bioassays with T1 plants revealed the Cry1Ia12 protein toxicity on Spodoptera frugiperda larvae, as evidenced by mortality up to 40% and a significant delay in the development of the target insects compared to untransformed controls (up to 30-fold). Also, an important reduction of Anthonomus grandis emerging adults (up to 60%) was observed when the insect larvae were fed on T1 floral buds. All the larvae and adult insect survivors on the transgenic lines were weaker and significantly smaller compared to the non-transformed plants. Therefore, this study provides GM cotton plant with simultaneous resistance against the Lepidopteran (S. frugiperda), and the Coleopteran (A. grandis) insect orders, and all data suggested that the Cry1Ia12 toxin could effectively enhance the cotton transgenic plants resistance to both insect pests.

High throughput Agrobacterium tumefaciens-mediated germline transformation of mechanically isolated meristem explants of cotton (Gossypium hirsutum L.)

Agrobacterium tumefaciens mediates high frequency of germline transformation of cotton meristem explants. The meristem transformation system we developed is rapid, high throughput and genotype-flexible. We have developed a high throughput cotton transformation system based on direct Agrobacterium inoculation of mechanically isolated meristem explants of cotton (Gossypium hirsutum L.). The explants were inoculated with a disarmed A. tumefaciens strain, AB33 harboring a 2 T-DNA binary vector pMON114908. This vector contained a gene of interest, an intron-disrupted β-glucuronidase gene in one T-DNA, and a selectable marker gene, aadA in the other T-DNA. Critical factors, such as method of co-culture, culture temperature during selection, composition of selection medium, and selection scheme were found to influence transformation frequency. The cycle time from initial inoculation to the transplanting of transgenic plants to soil was 7-8 weeks. Stable integration of transgenes and their transmission to progeny were confirmed by molecular and genetic analyses. Transgenes segregated in the expected Mendelian fashion in the T1 generation for most of the transgenic events. It was possible to recover marker-free events in the T1 generation when utilizing a binary vector that contained the selectable marker and gene of interest expression cassettes on independent T-DNAs. The procedure presented here has been used to regenerate thousands of independent transgenic events from multiple varieties with numerous constructs, and we believe it represents a major step forward in cotton transformation technology.

Genetically engineered crops: from idea to product

Genetically engineered crops were first commercialized in 1994 and since then have been rapidly adopted, enabling growers to more effectively manage pests and increase crop productivity while ensuring food, feed, and environmental safety. The development of these crops is complex and based on rigorous science that must be well coordinated to create a plant with desired beneficial phenotypes. This article describes the general process by which a genetically engineered crop is developed from an initial concept to a commercialized product.

Wuschel overexpression promotes somatic embryogenesis and induces organogenesis in cotton (Gossypium hirsutum L.) tissues cultured in vitro

This work shows that overexpression of the WUS gene from Arabidopsis enhanced the expression of embryogenic competence and triggered organogenesis from some cells of the regenerated embryo-like structures. Agrobacterium-mediated genetic transformation of cotton was described in the late 1980s, but is still time consuming and largely genotype dependant due to poor regeneration. To help solve this bottleneck, we over-expressed the WUSCHEL (WUS) gene, a homeobox transcription factor cloned in Arabidopsis thaliana, known to stimulate organogenesis and/or somatic embryogenesis in Arabidopsis tissues cultured in vitro. The AtWUS gene alone, and AtWUS gene fused to the GFP marker were compared to the GFP gene alone and to an empty construct used as a control. Somatic embryogenesis was improved in WUS expressed calli, as the percentage of explants giving rise to embryogenic tissues was significantly higher (×3) when WUS gene was over-expressed than in the control. An interesting result was that WUS embryogenic lines evolved in green embryo-like structures giving rise to ectopic organogenesis never observed in any of our previous transformation experiments. Using our standard in vitro culture protocol, the overexpression of AtWUS in tissues of a recalcitrant variety did not result in the production of regenerated plants. This achievement will still require the optimization of other non-genetic factors, such as the balance of exogenous phytohormones. However, our results suggest that targeted expression of the WUS gene is a promising strategy to improve gene transfer in recalcitrant cotton cultivars.

Agrobacterium-mediated transformation of cotton

There are many methods and techniques that can be used to transfer foreign genes into cells. In plant biotechnology, Agrobacterium-mediated transformation is a widely used traditional method for inserting foreign genes into plant genome and obtaining transgenic plants, particularly for dicot plant species. Agrobacterium-mediated transformation of cotton involves several important and also critical steps, which includes coculture of cotton explants with Agrobacterium, induction and selection of stable transgenic cell lines, recovery of plants from transgenic cells majorly through somatic embryogenesis, and detection and expression analysis of transgenic plants. In this chapter, we describe a detailed step-by-step protocol for obtaining transgenic cotton plants via Agrobacterium-mediated transformation.

Transgenic cotton: from biotransformation methods to agricultural application

Transgenic cotton is among the first transgenic plants commercially adopted around the world. Since it was first introduced into the field in the middle of 1990s, transgenic cotton has been quickly adopted by cotton farmers in many developed and developing countries. Transgenic cotton has offered many important environmental, social, and economic benefits, including reduced usage of pesticides, indirect increase of yield, minimizing environmental pollution, and reducing labor and cost. Agrobacterium-mediated genetic transformation method is the major method for obtaining transgenic cotton. However, pollen tube pathway-mediated method is also used, particularly by scientists in China, to breed commercial transgenic cotton. Although transgenic cotton plants with disease-resistance, abiotic stress tolerance, and improved fiber quality have been developed in the past decades, insect-resistant and herbicide-tolerant cotton are the two dominant transgenic cottons in the transgenic cotton market.

A chimeric arabinogalactan protein promotes somatic embryogenesis in cotton cell culture

Arabinogalactan proteins (AGPs) are a family of extracellular plant proteoglycans implicated in many aspects of plant growth and development, including in vitro somatic embryogenesis (SE). We found that specific AGPs were produced by cotton (Gossypium hirsutum) calli undergoing SE and that when these AGPs were isolated and incorporated into tissue culture medium, cotton SE was promoted. When the AGPs were partly or fully deglycosylated, SE-promoting activity was not diminished. Testing of AGPs separated by reverse-phase high-performance liquid chromatography revealed that the SE-promoting activity resided in a hydrophobic fraction. We cloned a full-length complementary DNA (cotton PHYTOCYANIN-LIKE ARABINOGALACTAN-PROTEIN1 [GhPLA1]) that encoded the protein backbone of an AGP in the active fraction. It has a chimeric structure comprising an amino-terminal signal sequence, a phytocyanin-like domain, an AGP-like domain, and a hydrophobic carboxyl-terminal domain. Recombinant production of GhPLA1 in tobacco (Nicotiana tabacum) cells enabled us to purify and analyze a single glycosylated AGP and to demonstrate that this chimeric AGP promotes cotton SE. Furthermore, the nonglycosylated phytocyanin-like domain from GhPLA1, which was bacterially produced, also promoted SE, indicating that the glycosylated AGP domain was unnecessary for in vitro activity.

Cotton pistil drip transformation method

Conventional plant transformation typically includes preparation of competent plant cells or tissues, delivery of foreign genes into cells, transformed cell selection with stable incorporated foreign genes, and regeneration of transformed cells into intact plants. This process traditionally relies on tissue culture, and cotton has not been an exception to this paradigm. Though the commercialization of transgenic cotton is a resounding success, cotton transformation, which is the first step in producing transgenic cotton, is a burdensome process since there is a very long tissue culture process and a limited number of cultivars that can be regenerated. An improved process which is easier to handle and more genotype independent could efficiently generate more transgenic plants and allow meaningful analyses of gene function and transgenic plants. Cotton pistil drip by inoculating Agrobacterium tumefaciens onto the pistil after pollination gave rise to stable transformants. Since this transformation process in cotton occurs following pollination and during fertilization (postanthesis) but not during preanthesis as in Arabidopsis, the mechanism by which Agrobacterium enters plant cells and integrates into the cotton genome may differ from that in Arabidopsis. This chapter provides the detailed protocol for pistil drip, a simple in planta transformation method without the plant tissue culture process.

Enhanced Agrobacterium-mediated transformation of embryogenic calli of upland cotton

Agrobacterium tumefaciens-mediated transformation of cotton embryogenic calli (EC) was enhanced by choosing appropriate EC and improving efficiency of coculture, selection cultivation, and plant regeneration. The binary vector pBI121 (containing a neomycin phosphotransferase II gene npt-II as a selection marker and a uidA gene as a reporter gene) was used to research transformation efficiency. After 48 h cocultivation, the number of β-glucuronidase (GUS)-positive calli characterized by yellow, loose, and fine-grained EC was twofold greater than that of gray, brown, and coarse granule EC. It indicated that the efficiency of transient transformation was affected by EC morphology. Transient transformation efficiency also was improved by cocultivation on the medium by adding 50 mg/L acetosyringone at 19°C for 48 h. Subculturing EC on the selection medium with low cell density increased the production of kanamycin-resistant (Km-R) calli lines. From an original 0.3 g EC, an average of 20 Km-R calli lines were obtained from a selection dish, and the GUS-positive rate of Km-R clones was 81.97%. A large number of normal plants were rapidly regenerated on the differentiation medium with dehydration treatments, and the GUS-positive rate of regeneration plants was about 72.6%. Polymerase chain reaction analysis of GUS-positive plantlets revealed a 100% positive detection rate for neomycin phosphotransferase II gene and gus gene. Southern blot of transgenic plants regenerated from different Km-R calli lines demonstrated that the target gene, mostly with the low copy number, was integrated into the cotton genome.

Heterologous expression of Aspen PTM3, a MADS box gene in cotton

The PTM3 gene of Aspen was ectopically expressed in cotton to explore the opportunity to introduce desirable agronomic traits with the potential to improve yield and modify the duration of the parent cotton variety. Sixty-seven transgenic cotton lines expressing Aspen PTM3 (MADS box) gene were developed. The transgenic cotton lines expressing PTM3 gene showed earliness of 4-15 days variations in flowering and maturity. The transgenic lines were confirmed by kanamycin leaf paint assay, GUS assay and PCR. Among 67 transgenic lines, the event-10 showed profuse branching, event-24 showed abnormal growth and the remaining events exhibited single erect phenotype. In addition, the event-24 produced no flower and this might be due to the positional effect of PTM3 gene integration. Southern blot analysis performed for event-10, 24 and 48 showed distinct single copy integrations of PTM3 gene cassette. GUS assay performed using various plant parts of event-10 showed constitutive expression of the transgene. In view of cotton breeding, among all the events, the event-10 was found to be phenotypically significant with earliness of 12 days in flowering and 15 days in maturity and yield enhancement of 27%. In addition, the event-10 showed no square dropping and allowed the plants to bear more number of bolls. Based on these results, event-10 was chosen to carry out the inheritance study of expressed characters in the progeny.

Coexpression of potato type I and II proteinase inhibitors gives cotton plants protection against insect damage in the field

Potato type I and II serine protease inhibitors are produced by solanaceous plants as a defense mechanism against insects and microbes. Nicotiana alata proteinase inhibitor (NaPI) is a multidomain potato type II inhibitor (pin II) that is produced at high levels in the female reproductive tissues of the ornamental tobacco, Nicotiana alata. The individual inhibitory domains of NaPI target the major classes of digestive enzymes, trypsin and chymotrypsin, in the gut of lepidopteran larval pests. Although consumption of NaPI dramatically reduced the growth and development of a major insect pest, Helicoverpa punctigera, we discovered that surviving larvae had high levels of chymotrypsin activity resistant to inhibition by NaPI. We found a potato type I inhibitor, Solanum tuberosum potato type I inhibitor (StPin1A), was a strong inhibitor of the NaPI-resistant chymotrypsin activity. The combined inhibitory effect of NaPI and StPin1A on H. armigera larval growth in the laboratory was reflected in the increased yield of cotton bolls in field trials of transgenic plants expressing both inhibitors. Better crop protection thus is achieved using combinations of inhibitors in which one class of proteinase inhibitor is used to match the genetic capacity of an insect to adapt to a second class of proteinase inhibitor.

Genetically engineering plants for crop improvement

Dramatic progress has been made in the development of gene transfer systems for higher plants. The ability to introduce foreign genes into plant cells and tissues and to regenerate viable, fertile plants has allowed for explosive expansion of our understanding of plant biology and has provided an unparalleled opportunity to modify and improve crop plants. Genetic engineering of plants offers significant potential for seed, agrichemical, food processing, specialty chemical, and pharmaceutical industries to develop new products and manufacturing processes. The extent to which genetically engineered plants will have an impact on key industries will be determined both by continued technical progress and by issues such as regulatory approval, proprietary protection, and public perception.

High-efficiency transformation by biolistics of soybean, common bean and cotton transgenic plants

This protocol describes a method for high-frequency recovery of transgenic soybean, bean and cotton plants, by combining resistance to the herbicide imazapyr as a selectable marker, multiple shoot induction from embryonic axes of mature seeds and biolistics techniques. This protocol involves the following stages: plasmid design, preparation of soybean, common bean and cotton apical meristems for bombardment, microparticle-coated DNA bombardment of apical meristems and in vitro culture and selection of transgenic plants. The average frequencies (the total number of fertile transgenic plants divided by the total number of bombarded embryonic axes) of producing germline transgenic soybean and bean and cotton plants using this protocol are 9, 2.7 and 0.55%, respectively. This protocol is suitable for studies of gene function as well as the production of transgenic cultivars carrying different traits for breeding programs. This protocol can be completed in 7-10 months.

Development and commercial use of Bollgard cotton in the USA--early promises versus today's reality

Bollgard cotton is the trademark given to a number of varieties of cotton bio-engineered to produce an insecticidal protein from Bacillus thuringiensis (Bt). When produced by the modified cotton plants, this protein controls certain lepidopterous cotton insect pests. Commercially available since 1996, these cotton varieties are purchased under a license agreement in which the growers pay a fee and agree to abide by the terms, which include a 1-year license to use the technology and agreement to participate in an insect resistance management program. Today, Bollgard cotton is grown on more than one-third of all cotton acreage in the USA. This product has reduced cotton production costs and insecticide use by providing an effective alternative to chemical insecticides for the control of tobacco budworm, Heliothis virescens; cotton bollworm, Helicoverpa zea; and pink bollworm, Pectinophora gossypiella. The specificity and safety profile of the Bt protein produced in planta in cotton was maintained. It has retained its selectivity for lepidopterous insects and lacks the characteristics found in potential allergenic proteins. Fiber quality, the agronomic characteristics of the plant and seed composition remain unchanged. New cotton technology is being developed to provide improved insect control and a wider spectrum of activity. These future products could further reduce insecticide use in the production of cotton, while maintaining the high level of safety and reliability that has been demonstrated by five seasons of Bollgard cotton use.

In vitro induction of multiple shoots and plant regeneration in cotton (Gossypium hirsutum L.)

Induction of multiple shoots in cotton (Gossypium hirsutum L. cv. Anjali-LRK 516) has been achieved with cotyledonary nodes devoid of cotyledons and apical meristems. Explants from 35-day-old seedlings yielded the maximum number of shoots (4.7 shoots/explant) using Murashige and Skoog (MS) basal medium supplemented with 6-benzylaminopurine and kinetin (2.5 mg/1 each). Explants from 35-day-old seedlings raised in glass bottles produced a higher number of multiple shoots (8.3 shoots/explant) than those grown in glass tubes and cultured on the same shoot induction medium. Elongation of multiple shoots was obtained on liquid or agar MS basal medium without phytohormones. In vitro shoots were rooted on half-strength agar-solidified MS basal medium or with 0.05 or 0.1 mg/1 naphthaleneacetic acid. Hardening and survival of tissue culture plantlets was 95% under greenhouse conditions.

Metabolic pathway engineering in cotton: biosynthesis of polyhydroxybutyrate in fiber cells

Alcaligenes eutrophus genes encoding the enzymes, beta-ketothiolase (phaA), acetoacetyl-CoA reductase (phaB), and polyhydroxyalkanoate synthase (phaC) catalyze the production of aliphatic polyester poly-d-(-)-3-hydroxybutyrate (PHB) from acetyl-CoA. PHB is a thermoplastic polymer that may modify fiber properties when synthesized in cotton. Endogenous beta-ketothiolase activity is present in cotton fibers. Hence cotton was transformed with engineered phaB and phaC genes by particle bombardment, and transgenic plants were selected based on marker gene, beta-glucuronidase (GUS), expression. Fibers of 10 transgenic plants expressed phaB gene, while eight plants expressed both phaB and phaC genes. Electron microscopy examination of fibers expressing both genes indicated the presence of electron-lucent granules in the cytoplasm. High pressure liquid chromatography, gas chromatography, and mass spectrometry evidence suggested that the new polymer produced in transgenic fibers is PHB. Sixty-six percent of the PHB in fibers is in the molecular mass range of 0.6 x 10(6) to 1.8 x 10(6) Da. The presence of PHB granules in transgenic fibers resulted in measurable changes of thermal properties. The fibers exhibited better insulating characteristics. The rate of heat uptake and cooling was slower in transgenic fibers, resulting in higher heat capacity. These data show that metabolic pathway engineering in cotton may enhance fiber properties by incorporating new traits from other genetic sources. This is an important step toward producing new generation fibers for the textile industry.

Engineering 2,4-D resistance into cotton

To reduce damage by drift-levels of the herbicide 2,4-dichlorophenoxyacetic acid, we have engineered the 2,4-D resistance trait into cotton (Gossypium hirsutum L.). The 2,4-D monooxygenase gene tfdA from Alcaligenes eutrophus plasmid pJP5 was isolated, modified and expressed in transgenic tobacco and cotton plants. Analyses of the transgenic progeny showed stable transmission of the chimeric tfdA gene and production of active 2,4-D monooxygenase. Cotton plants obtained were tolerant to 3 times the field level of 2,4-D used for wheat, corn, sorghum and pasture crops.

Insect resistant cotton plants

We have expressed truncated forms of the insect control protein genes of Bacillus thuringiensis var. kurstaki HD-1(cryIA(b) and HD-73 (cryIA(c) in cotton plants at levels that provided effective control of agronomically important lepidopteran insect pests. Total protection from insect damage of leaf tissue from these plants was observed in laboratory assays when tested with two lepidopteran insects, an insect relatively sensitive to the B.t.k. insect control protein, Trichoplusia ni (cabbage looper) and an insect that is 100 fold less sensitive, Spodoptera exigua (beet armyworm). Whole plants, assayed under conditions of high insect pressure with Heliothis zea (cotton bollworm) showed effective square and boll protection. Immunological analysis of the cotton plants indicated that the insect control protein represented 0.05% to 0.1% of the total soluble protein. We view these results as a major step towards the agricultural use of genetically modified plants with insect resistance in this valuable, high acreage crop.