Genetic transformation of mosquitoes by microparticle bombardment

Mosquitoes constitute the major living beings causing human deaths in the world. They are vectors of malaria, yellow fever, dengue, zika, filariases, chikungunya, among other diseases. New strategies to control/eradicate mosquito populations are based on newly developed genetic manipulation techniques. However, genetic transformation of mosquitoes is a major technical bottleneck due to low efficiency, the need of sophisticated equipment, and highly trained personnel. The present report shows the transgenerational genetic transformation of Aedes aegypti, using the particle inflow gun (PIG), by integrating the ecfp gene in the AAEL000582 mosquito gene with the CRISPR-Cas9 technique, achieving a mean efficiency of 44.5% of bombarded individuals (G0) that showed ECFP expression in their tissues, and a mean of 28.5% transformation efficiency measured on G1 individuals. The same transformation technique was used to integrate the egfp/scorpine genes cloned in the Minos transposon pMinHygeGFP into the Anopheles albimanus genome, achieving a mean efficiency of 43.25% of bombarded individuals (G0) that showed EGFP expression in their tissues. Once the technique was standardized, transformation of Ae. aegypti neonate larvae and An. albimanus eggs was achieved when exposed to gold microparticle bombardment. Integration of genes and heterologous protein expression were confirmed by PCR, sequencing, fluorescent microscopy, mass spectrometry, Western blot and dot blot analyses. Transgenerational inheritance of the transgenes was observed only on Ae. aegypti, as all transformed An. albimanus individuals died at the pupal stage of the G0 generation.

Agrobacterium rhizogenes-mediated transformation of grain (Amaranthus hypochondriacus) and leafy (A. hybridus) amaranths

Transgenic A. hypochondriacus and A. hybridus roots were generated. Further, a distinct plant regeneration program via somatic embryos produced from hairy roots was established. Work was implemented to develop an optimized protocol for root genetic transformation of the three grain amaranth species and A. hybridus, their presumed ancestor. Transformation efficiency was species-specific, being higher in A. hypochondriacus and followed by A. hybridus. Amaranthus cruentus and A. caudatus remained recalcitrant. A reliable and efficient Agrobacteruim rhizogenes-mediated transformation of these species was established using cotyledon explants infected with the previously untested BVG strain. Optimal OD₆₀₀ bacterial cell densities were 0.4 and 0.8 for A. hypochondriacus and A. hybridus, respectively. Hairy roots of both amaranth species were validated by the amplification of appropriate marker genes and, when pertinent, by monitoring green fluorescent protein emission or β-glucuronidase activity. Embryogenic calli were generated from A. hypochondriacus rhizoclones. Subsequent somatic embryo maturation and germination required the activation of cytokinin signaling, osmotic stress, red light, and calcium incorporation. A crucial step to ensure the differentiation of germinating somatic embryos into plantlets was their individualization and subcultivation in 5/5 media containing 5% sucrose, 5 g/L gelrite, and 0.2 mg/L 2-isopentenyladenine (2iP) previously acidified to pH 4.0 with phosphoric acid, followed by their transfer to 5/5 + 2iP media supplemented with 100 mg/L CaCl₂. These steps were strictly red light dependent. This process represents a viable protocol for plant regeneration via somatic embryo germination from grain amaranth transgenic hairy roots. Its capacity to overcome the recalcitrance to genetic transformation characteristic of grain amaranth has the potential to significantly advance the knowledge of several unresolved biological aspects of grain amaranths.

Development of an Efficient Protocol to Obtain Transgenic Coffee, Coffea arabica L., Expressing the Cry10Aa Toxin of Bacillus thuringiensis

This report presents an efficient protocol of the stable genetic transformation of coffee plants expressing the Cry10Aa protein of Bacillus thuringiensis. Embryogenic cell lines with a high potential of propagation, somatic embryo maturation, and germination were used. Gene expression analysis of cytokinin signaling, homedomains, auxin responsive factor, and the master regulators of somatic embryogenesis genes involved in somatic embryo maturation were evaluated. Plasmid pMDC85 containing the cry10Aa gene was introduced into a Typica cultivar of C. arabica L. by biobalistic transformation. Transformation efficiency of 16.7% was achieved, according to the number of embryogenic aggregates and transgenic lines developed. Stable transformation was proven by hygromycin-resistant embryogenic lines, green fluorescent protein (GFP) expression, quantitative analyses of Cry10Aa by mass spectrometry, Western blot, ELISA, and Southern blot analyses. Cry10Aa showed variable expression levels in somatic embryos and the leaf tissue of transgenic plants, ranging from 76% to 90% of coverage of the protein by mass spectrometry and from 3.25 to 13.88 μg/g fresh tissue, with ELISA. qPCR-based 2^−ΔΔCt trials revealed high transcription levels of cry10Aa in somatic embryos and leaf tissue. This is the first report about the stable transformation and expression of the Cry10Aa protein in coffee plants with the potential for controlling the coffee berry borer.

Transcriptomic analysis of basidiocarp development in Ustilago maydis (DC) Cda

Previously, we demonstrated that when Ustilago maydis (DC) Cda., a phytopathogenic basidiomycete and the causal agent of corn smut, is grown in the vicinity of maize embryogenic calli in a medium supplemented with the herbicide Dicamba, it developed gastroid-like basidiocarps. To elucidate the molecular mechanisms involved in the basidiocarp development by the fungus, we proceeded to analyze the transcriptome of the process, identifying a total of 2002 and 1064 differentially expressed genes at two developmental stages, young and mature basidiocarps, respectively. Function of these genes was analyzed with the use of different databases. MIPS analysis revealed that in the stage of young basidiocarp, among the ca. two thousand differentially expressed genes, there were some previously described for basidiocarp development in other fungal species. Additional elements that operated at this stage included, among others, genes encoding the transcription factors FOXO3, MIG3, PRO1, TEC1, copper and MFS transporters, and cytochromes P450. During mature basidiocarp development, important up-regulated genes included those encoding hydrophobins, laccases, and ferric reductase (FRE/NOX). The demonstration that a mapkk mutant was unable to form basidiocarps, indicated the importance of the MAPK signaling pathway in this developmental process.

The Phaseolus vulgaris PvTRX1h gene regulates plant hormone biosynthesis in embryogenic callus from common bean

Common bean is the most important grain legume in the human diet. Bean improvement efforts have been focused on classical breeding techniques because bean is recalcitrant to both somatic embryogenesis and in vitro regeneration. This study was undertaken to better understand the process of somatic embryogenesis in the common bean. We focused on the mechanisms by which somatic embryogenesis in plants is regulated and the interaction of these mechanisms with plant hormones. Specifically, we examined the role of the gene PvTRX1h, an ortholog of a major known histone lysine methyltransferase in plants, in somatic embryo generation. Given the problems with regeneration and transformation, we chose to develop and use regeneration-competent callus that could be successively transformed. Embryogenic calli of common bean were generated and transformed with the PvTRX1hRiA construction to down-regulate, by RNA interference, expression of the PvTRX1h gene. Plant hormone content was measured by mass spectrometry and gene expression was assessed by q-PCR. Detailed histological analysis was performed on selected transgenic embryogenic calli. It was determined that down-regulation of PvTRX1h gene was accompanied by altered concentrations of plant hormones in the calli. PvTRX1h regulated the expression of genes involved in auxin biosynthesis and embryogenic calli in which PvTRX1h was down-regulated were capable of differentiation into somatic embryos. Also, down-regulation of PvTRX1h showed increased transcript abundance of a gene coding for a second histone lysine methyltransferase, PvASHH2h. Accordingly, the PvTRX1h gene is involved in the synthesis of plant hormones in common bean callus. These results shed light on the crosstalk among histone methyltransferases and plant hormone signaling and on gene regulation during somatic embryo generation.

AtTCTP2, an Arabidopsis thaliana homolog of Translationally Controlled Tumor Protein, enhances in vitro plant regeneration

The Translationally Controlled Tumor Protein (TCTP) is a central regulator of cell proliferation and differentiation in animals, and probably also in plants. Arabidopsis harbors two TCTP genes, AtTCTP1 (At3g16640), which is an important mitotic regulator, and AtTCTP2 (At3g05540), which is considered a pseudogene. Nevertheless, we have obtained evidence suggesting that this gene is functional. Indeed, a T-DNA insertion mutant, SALK_045146, displays a lethal phenotype during early rosette stage. Also, both the AtTCTP2 promoter and structural gene are functional, and heterozygous plants show delayed development. AtTCTP1 cannot compensate for the loss of AtTCTP2, since the accumulation levels of the AtTCTP1 transcript are even higher in heterozygous plants than in wild-type plants. Leaf explants transformed with Agrobacterium rhizogenes harboring AtTCTP2, but not AtTCTP1, led to whole plant regeneration with a high frequency. Insertion of a sequence present in AtTCTP1 but absent in AtTCTP2 demonstrates that it suppresses the capacity for plant regeneration; also, this phenomenon is enhanced by the presence of TCTP (AtTCTP1 or 2) in the nuclei of root cells. This confirms that AtTCTP2 is not a pseudogene and suggests the involvement of certain TCTP isoforms in vegetative reproduction in some plant species.

Metamorphosis of the Basidiomycota Ustilago maydis: transformation of yeast-like cells into basidiocarps

Ustilago maydis (DC) Cda., a phytopathogenic Basidiomycota, is the causal agent of corn smut. During its life cycle U. maydis alternates between a yeast-like, haploid nonpathogenic stage, and a filamentous, dikaryotic pathogenic form that invades the plant and induces tumor formation. As all the members of the Subphylum Ustilaginomycotina, U. maydis is unable to form basidiocarps, instead it produces teliospores within the tumors that germinate forming a septate basidium (phragmobasidium). We have now established conditions allowing a completely different developmental program of U. maydis when grown on solid medium containing auxins in dual cultures with maize embryogenic calli. Under these conditions U. maydis forms large hemi-spheroidal structures with all the morphological and structural characteristics of gastroid-type basidiocarps. These basidiocarps are made of three distinct hyphal layers, the most internal of which (hymenium) contains non-septate basidia (holobasidia) from which four basidiospores develop. In basidiocarps meiosis and genetic recombination occur, and meiotic products (basidiospores) segregate in a Mendelian fashion. These results are evidence of sexual cycle completion of an Ustilaginomycotina in vitro, and the demonstration that, besides its quasi-obligate biotrophic pathogenic mode of life, U. maydis possesses the genetic program to form basidiocarps as occurs in saprophytic Basidiomycota species.

Infection, transfection, and co-transfection of baculoviruses by microprojectile bombardment of larvae

The use of baculoviruses as expression vectors for heterologous proteins has been practically limited to the use of the Autographa californica multiple nucleopolyhedrovirus (AcMNPV). In this work, infection, transfection and co-transfection events with the baculoviruses AcMNPV and Trichoplusia ni granulovirus (TnGV) were accomplished by bombardment of T. ni first-instar larvae with microprojectiles coated with virions, viral DNA, and viral DNA and a transfer vector, respectively. A series of shooting conditions were tested until positive results were obtained. The use of 1.6 microm gold particles at 900 psi shooting pressure, 400 Torr vacuum, 7 cm distance to target, on sets of 20 first-instar larvae held in a 16 mm diameter container, proved to be the best shooting conditions. Typical infection symptoms were shown by larvae when shot with viruses or viral DNA from AcMNPV or TnGV. Co-transfected recombinant AcMNPV and TnGV were identified by the formation of occlusion bodies and GFP, respectively, in bombarded larvae. This technique opens a wide range of possibilities, not only to use an extensive number of baculoviruses as expression vectors for heterologous proteins, but also be used to infect, transfect or co-transfect a wide variety of viruses into animal cells.

Establishment, characterization and plant regeneration from highly chlorophyllous embryogenic cell cultures of blue grama grass, Bouteloua gracilis (H.B.K.) Lag. ex Steud

 A finely dispersed, homogeneous and highly chlorophyllous cell suspension (TIANSJ98 cell line) was obtained from shoot apices of Bouteloua gracilis (H.B.K.) Lag. ex Steud. cultured on MPC medium containing MS salts supplemented with 2,4-D (1 mg/l), BAP (2 mg/l) and adenine (40 mg/l). When the TIANSJ98 cell line was grown in this medium with shaking at 180 rpm it had doubling times of 7.2 and 3.7 days in terms of fresh and dry weight, respectively. Total chlorophyll content in this cell culture ranged from 121.6 to 18.3 μg/g FW at 12 and 21 days following culture initiation. Plants regenerated from the TIANSJ98 cell line, via somatic embryogenesis, were grown to maturity and produced seeds. Although different cell culture systems have been described for cereals and grasses, to the best of our knowledge this is the first report of a highly chlorophyllous and regenerable cell suspension in Poaceae.

Completion of the sexual cycle and demonstration of genetic recombination in Ustilago maydis in vitro

The heterobasidiomycetes responsible for plant smuts obligatorily require their hosts for the completion of the sexual cycle. Accordingly, the sexual cycle of these fungi could so far be studied only by infecting host plants. We have now induced Ustilago maydis, the causative agent of corn smut, to traverse the whole life cycle by growing mixtures of mating-compatible strains of the fungus on a porous membrane placed on top of embryogenic cell cultures of its host Zea mays. Under these conditions, mating, karyogamy and meiosis take place, and the fungus induces differentiation of the plant cells. These results suggest that embryogenic maize cells produce diffusible compounds needed for completion of the sexual cycle of U. maydis, as the plant does for the pathogen during infection.

Analysis of an abscisic acid (ABA)-responsive gene promoter belonging to the Asr gene family from tomato in homologous and heterologous systems

Asr is a family of genes that maps to chromosome 4 of tomato. Asr2, a recently reported member of this family, is believed to be regulated by abscisic acid (ABA), stress and ripening. A genomic Asr2 clone has been fully sequenced, and candidate upstream regulatory elements have been identified. To prove that the promoter region is functional in vivo, we fused it upstream of the beta-glucuronidase (GUS) reporter gene. The resulting chimeric gene fusion was used for transient expression assays in papaya embryogenic calli and leaves. In addition, the same construct was used to produce transgenic tomato, papaya, tobacco, and potato plants. Asr2 upstream sequences showed promoter function in all of these systems. Under the experimental conditions tested, ABA stimulated GUS expression in papaya and tobacco, but not in tomato and potato systems.

Agrobacterium-mediated transformation of Amaranthus hypochondriacus: light- and tissue-specific expression of a pea chlorophyll a/b-binding protein promoter

Mature embryos of Amaranthus hypochondriacus (amaranth) were used to develop an in vitro culture system for plant regeneration and genetic transformation. Plants were regenerated from embryo-derived callus cultivated on Murashige and Skoog medium supplemented with 10 µM 2,4-dichlorophenoxyacetic acid or 3,6-dichloro-2-methoxybenzoic acid and 10% coconut liquid endosperm. Transgenic plants were obtained by inoculation of mature embryo explants with a disarmed Agrobacterium strain containing the plasmid pGV2260(pEsc4), which carried the genes encoding neomycin phosphotransferase type II and β-glucuronidase. The presence of transgenes in the genome of transformed amaranth plants and their progeny was demonstrated by Southern blot hybridization. Tissue specific and light-inducible expression directed by a pea chlorophyll a/b-binding protein promoter was observed in transgenic amaranth plants and their progeny.

Aluminum tolerance in transgenic plants by alteration of citrate synthesis

Aluminum when in soluble form, as found in acidic soils that comprise about 40 percent of the world's arable land, is toxic to many crops. Organic acid excretion has been correlated with aluminum tolerance in higher plants. Overproduction of citrate was shown to result in aluminum tolerance in transgenic tobacco (Nicotiana tabacum) and papaya (Carica papaya) plants.

Herbicide resistant transgenic papaya plants produced by an efficient particle bombardment transformation method

A system for the production of transgenic papaya (Carica papaya L.) plants using zygotic embryos and embryogenic callus as target cells for particle bombardment is described. Phosphinothricin (bar ) and kanamycin (npt II) resistance genes were used as selectable markers, and the gus gene (uidA) as a reporter gene. Selection with 100 mg/l kanamycin and 4 mg/l phosphinothricin (PPT) yielded a total of over 90 resistant embryogenic colonies from three independent experiments using embryogenic callus as a target tissue. This represents an efficiency of 60 transgenic clones per gram of fresh weight callus bombarded. The efficiency of genetic transformation using zygotic embryos was lower, as only 8 independent resistant clones were recovered out of 645 bombarded zygotic embryos, giving a efficiency of 1.24%. Subsequent subculture of transgenic somatic embryos both from zygotic embryos and embryogenic callus led to the development of plants with apparently normal morphology. Histological, fluorimetric assay for GUS, NPT II assay and DNA analysis (Southern hybridization) showed that kanamycin /PPT resistant plants carried and expressed the transgenes.