Upstream sequences regulating legumin gene expression in heterologous transgenic plants

Biofortification of safflower: an oil seed crop engineered for ALA-targeting better sustainability and plant based omega-3 fatty acids

Alpha-linolenic acid (ALA) deficiency and a skewed n6:n3 fatty acid ratio in the diet is a major explanation for the prevalence of cardiovascular diseases and inflammatory/autoimmune diseases. There is mounting evidence of the health benefits associated with omega-3 long chain polyunsaturated fatty acids (LC PUFA's). Although present in abundance in fish, a number of factors limit our consumption of fish based omega-3 PUFA's. To name a few, overexploitation of wild fish stocks has reduced their sustainability due to increased demand of aquaculture for fish oil and meal; the pollution of marine food webs has raised concerns over the ingestion of toxic substances such as heavy metals and dioxins; vegetarians do not consider fish-based sources for supplemental nutrition. Thus alternative sources are being sought and one approach to the sustainable supply of LC-PUFAs is the metabolic engineering of transgenic plants with the capacity to synthesize n3 LC-PUFAs. The present investigation was carried out with the goal of developing transgenic safflower capable of producing pharmaceutically important alpha-linolenic acid (ALA, C18:3, n3). This crop was selected as the seeds accumulate ~ 78% of the total fatty acids as linoleic acid (LA, C18:2, n6), the immediate precursor of ALA. In the present work, ALA production was achieved successfully in safflower seeds by transforming safflower hypocotyls with Arabidopsis specific delta 15 desaturase (FAD3) driven by truncated seed specific promoter. Transgenic safflower fortified with ALA is not only potentially valuable nutritional superior novel oil but also has reduced ratio of LA to ALA which is required for good health.

Temporal and spatial control of gene expression in horticultural crops

Biotechnology provides plant breeders an additional tool to improve various traits desired by growers and consumers of horticultural crops. It also provides genetic solutions to major problems affecting horticultural crops and can be a means for rapid improvement of a cultivar. With the availability of a number of horticultural genome sequences, it has become relatively easier to utilize these resources to identify DNA sequences for both basic and applied research. Promoters play a key role in plant gene expression and the regulation of gene expression. In recent years, rapid progress has been made on the isolation and evaluation of plant-derived promoters and their use in horticultural crops, as more and more species become amenable to genetic transformation. Our understanding of the tools and techniques of horticultural plant biotechnology has now evolved from a discovery phase to an implementation phase. The availability of a large number of promoters derived from horticultural plants opens up the field for utilization of native sequences and improving crops using precision breeding. In this review, we look at the temporal and spatial control of gene expression in horticultural crops and the usage of a variety of promoters either isolated from horticultural crops or used in horticultural crop improvement.

Isolation and functional characterization of a novel seed-specific promoter region from peanut

The importance of using tissue-specific promoters in the genetic transformation of plants has been emphasized increasingly. Here, we report the isolation of a novel seed-specific promoter region from peanut and its validation in Arabidopsis and tobacco seeds. The reported promoter region referred to as groundnut seed promoter (GSP) confers seed-specific expression in heterologous systems, which include putative promoter regions of the peanut (Arachis hypogaea L.) gene 8A4R19G1. This region was isolated, sequenced, and characterized using gel shift assays. Tobacco transgenics obtained using binary vectors carrying uidA reporter gene driven by GSP and/or cauliflower mosaic virus 35S promoters were confirmed through polymerase chain reaction (PCR), RT-PCR, and computational analysis of motifs which revealed the presence of TATA, CAAT boxes, and ATG signals. This seed-specific promoter region successfully targeted the reporter uidA gene to seed tissues in both Arabidopsis and tobacco model systems, where its expression was confirmed by histochemical analysis of the transgenic seeds. This promoter region is routinely being used in the genetic engineering studies in legumes aimed at targeting novel transgenes to the seeds, especially those involved in micronutrient enhancement, fungal resistance, and molecular pharming.

A noninvasive platform for imaging and quantifying oil storage in submillimeter tobacco seed

While often thought of as a smoking drug, tobacco (Nicotiana spp.) is now considered as a plant of choice for molecular farming and biofuel production. Here, we describe a noninvasive means of deriving both the distribution of lipid and the microtopology of the submillimeter tobacco seed, founded on nuclear magnetic resonance (NMR) technology. Our platform enables counting of seeds inside the intact tobacco capsule to measure seed sizes, to model the seed interior in three dimensions, to quantify the lipid content, and to visualize lipid gradients. Hundreds of seeds can be simultaneously imaged at an isotropic resolution of 25 µm, sufficient to assess each individual seed. The relative contributions of the embryo and the endosperm to both seed size and total lipid content could be assessed. The extension of the platform to a range of wild and cultivated Nicotiana species demonstrated certain evolutionary trends in both seed topology and pattern of lipid storage. The NMR analysis of transgenic tobacco plants with seed-specific ectopic expression of the plastidial phosphoenolpyruvate/phosphate translocator, displayed a trade off between seed size and oil concentration. The NMR-based assay of seed lipid content and topology has a number of potential applications, in particular providing a means to test and optimize transgenic strategies aimed at the manipulation of seed size, seed number, and lipid content in tobacco and other species with submillimeter seeds.

Functional analysis and expression profiling of HcrVf1 and HcrVf2 for development of scab resistant cisgenic and intragenic apples

Apple scab resistance genes, HcrVf1 and HcrVf2, were isolated including their native promoter, coding and terminator sequences. Two fragment lengths (short and long) of the native gene promoters and the strong apple rubisco gene promoter (P(MdRbc)) were used for both HcrVf genes to test their effect on expression and phenotype. The scab susceptible cultivar 'Gala' was used for plant transformations and after selection of transformants, they were micrografted onto apple seedling rootstocks for scab disease tests. Apple transformants were also tested for HcrVf expression by quantitative RT-PCR (qRT-PCR). For HcrVf1 the long native promoter gave significantly higher expression that the short one; in case of HcrVf2 the difference between the two was not significant. The apple rubisco gene promoter proved to give the highest expression of both HcrVf1 and HcrVf2. The top four expanding leaves were used initially for inoculation with monoconidial isolate EU-B05 which belongs to race 1 of V. inaequalis. Later six other V. inaequalis isolates were used to study the resistance spectra of the individual HcrVf genes. The scab disease assays showed that HcrVf1 did not give resistance against any of the isolates tested regardless of the expression level. The HcrVf2 gene appeared to be the only functional gene for resistance against Vf avirulent isolates of V. inaequalis. HcrVf2 did not provide any resistance to Vf virulent strains, even not in case of overexpression. In conclusion, transformants carrying the apple-derived HcrVf2 gene in a cisgenic as well as in an intragenic configuration were able to reach scab resistance levels comparable to the Vf resistant control cultivar obtained by classical breeding, cv. 'Santana'.

Seed-specific elevation of non-symbiotic hemoglobin AtHb1: beneficial effects and underlying molecular networks in Arabidopsis thaliana

BACKGROUND

Seed metabolism is dynamically adjusted to oxygen availability. Processes underlying this auto-regulatory mechanism control the metabolic efficiency under changing environmental conditions/stress and thus, are of relevance for biotechnology. Non-symbiotic hemoglobins have been shown to be involved in scavenging of nitric oxide (NO) molecules, which play a key role in oxygen sensing/balancing in plants and animals. Steady state levels of NO are suggested to act as an integrator of energy and carbon metabolism and subsequently, influence energy-demanding growth processes in plants.

RESULTS

We aimed to manipulate oxygen stress perception in Arabidopsis seeds by overexpression of the non-symbiotic hemoglobin AtHb1 under the control of the seed-specific LeB4 promoter. Seeds of transgenic AtHb1 plants did not accumulate NO under transient hypoxic stress treatment, showed higher respiratory activity and energy status compared to the wild type. Global transcript profiling of seeds/siliques from wild type and transgenic plants under transient hypoxic and standard conditions using Affymetrix ATH1 chips revealed a rearrangement of transcriptional networks by AtHb1 overexpression under non-stress conditions, which included the induction of transcripts related to ABA synthesis and signaling, receptor-like kinase- and MAP kinase-mediated signaling pathways, WRKY transcription factors and ROS metabolism. Overexpression of AtHb1 shifted seed metabolism to an energy-saving mode with the most prominent alterations occurring in cell wall metabolism. In combination with metabolite and physiological measurements, these data demonstrate that AtHb1 overexpression improves oxidative stress tolerance compared to the wild type where a strong transcriptional and metabolic reconfiguration was observed in the hypoxic response.

CONCLUSIONS

AtHb1 overexpression mediates a pre-adaptation to hypoxic stress. Under transient stress conditions transgenic seeds were able to keep low levels of endogenous NO and to maintain a high energy status, in contrast to wild type. Higher weight of mature transgenic seeds demonstrated the beneficial effects of seed-specific overexpression of AtHb1.

Phylogenetic footprints in fern spore- and seed-specific gene promoters

Spermatophyte seed-storage proteins have descended from a group of proteins involved in cellular desiccation/hydration processes. Conserved protein structures are found across all plant phyla and in the fungi and Archaea. We investigated whether conservation in the coding region sequence is paralleled by common gene regulatory processes. Seed- and spore-specific gene promoters of three phylogenetically diverse plants were analysed by transient and transgenic expression in Arabidopsis thaliana and tobacco. The transcription factors FUS3 and ABI3, which are central regulators of seed maturation processes, interact with cis-motifs of seed-specific promoters from distantly related plants. The promoter of a fern spore-specific gene encoding a seed-storage globulin-like protein exhibits strong seed-specific activity in both Arabidopsis and tobacco. The existence of phylogenetic footprints indicates good conservation of regulatory pathways controlling gene expression in fern spores and in gymnosperm and angiosperm seeds, reflecting the concerted evolution of coding and regulatory regions.

Antisense inhibition of the plastidial glucose-6-phosphate/phosphate translocator in Vicia seeds shifts cellular differentiation and promotes protein storage

The glucose-6-phosphate/phosphate translocator (GPT) acts as an importer of carbon into the plastid. Despite the potential importance of GPT for storage in crop seeds, its regulatory role in biosynthetic pathways that are active during seed development is poorly understood. We have isolated GPT1 from Vicia narbonensis and studied its role in seed development using a transgenic approach based on the seed-specific legumin promoter LeB4. GPT1 is highly expressed in vegetative sink tissues, flowers and young seeds. In the embryo, localized upregulation of GPT1 at the onset of storage coincides with the onset of starch accumulation. Embryos of transgenic plants expressing antisense GPT1 showed a significant reduction (up to 55%) in the specific transport rate of glucose-6-phosphate as determined using proteoliposomes prepared from embryos. Furthermore, amyloplasts developed later and were smaller in size, while the expression of genes encoding plastid-specific translocators and proteins involved in starch biosynthesis was decreased. Metabolite analysis and stable isotope labelling demonstrated that starch biosynthesis was also reduced, although storage protein biosynthesis increased. This metabolic shift was characterized by upregulation of genes related to nitrogen uptake and protein storage, morphological variation of the protein-storing vacuoles, and a crude protein content of mature seeds of transgenics that was up to 30% higher than in wild-type. These findings provide evidence that (1) the prevailing level of GPT1 abundance/activity is rate-limiting for the synthesis of starch in developing seeds, (2) GPT1 exerts a controlling function on assimilate partitioning into storage protein, and (3) GPT1 is essential for the differentiation of embryonic plastids and seed maturation.

Mutated TATA-box/TATA binding protein complementation system for regulated transgene expression in tobacco

A two-component expression system was developed to achieve tightly regulated expression of transgenes in plants. One component functioned as an expression module whereas the other functioned as a regulatory module. The expression module comprised a highly expressing TATA-dependent seed-specific promoter in which the TATA motif in the core promoter was mutated to TGTA. The regulatory module expressed a mutated general transcription factor TBPm(3) that recognized TGTA and initiated transcription. Vectors were designed using component one alone or in combination with component two, and were transformed into tobacco. The TGTA mutation in the TATA-box completely inactivated the promoter, making component one non-functional. This non-functional module became transcriptionally active in the presence of the component two that expressed TBPm(3). The reporter gene gusA was expressed from the TGTA-containing chimeric legumin promoter, in a tightly seed-specific manner, in transgenic tobacco plants in the presence of TBPm(3) that was expressed from a constitutive promoter. The results show that the TGTA and TBPm(3) combination can be used to achieve high-level tissue-specific expression of TATA-dependent promoters.

A novel transcriptional cascade regulating expression of heat stress proteins during seed development of Arabidopsis

Within the Arabidopsis thaliana family of 21 heat stress transcription factors (Hsfs), HsfA9 is exclusively expressed in late stages of seed development. Here, we present evidence that developmental expression of HsfA9 is regulated by the seed-specific transcription factor ABSCISIC ACID-INSENSITIVE3 (ABI3). Intriguingly, ABI3 knockout lines lack detectable levels of HsfA9 transcript and protein, and further ectopic expression of ABI3 conferred the ability to accumulate HsfA9 in response to abscisic acid in transgenic plantlets. Consequently, the most abundant heat stress proteins (Hsps) in seeds (Hsp17.4-CI, Hsp17.7-CII, and Hsp101) were not detectable in the ABI3 knockout lines, but their expression could be detected in plants ectopically expressing HsfA9 in vegetative tissues. Furthermore, this seed-specific transcription factor cascade was reconstructed in transient beta-glucuronidase reporter assays in mesophyll protoplasts by showing that ABI3 could activate the HsfA9 promoter, whereas HsfA9 in turn was shown to be a potent activator on the promoters of Hsp genes. Thus, our study establishes a genetic framework in which HsfA9 operates as a specialized Hsf for the developmental expression of Hsp genes during seed maturation.

Seed-specific promoters direct gene expression in non-seed tissue

The organ specificity of four promoters that are known to direct seed-specific gene expression was tested. Whereas the phaseolin (phas)- and legumin B4 (leB4)-promoters were from genes encoding 7S and 11S globulins from Phaseolus vulgaris and Vicia faba, respectively, the usp- and the sbp-promoters were from non-storage protein genes of V. faba. The expression of different promoter-reporter gene fusions was followed either by RT-PCR or by registering the reporter enzyme activity in organs of transgenic tobacco, pea, narbon bean, or linseed. In addition to seeds, the promoters directed reporter gene expression in pollen and in seed coats. USP-, vicilin- and legumin-mRNA were detected by RT-PCR in pollen of Pisum sativum and V. faba. Expression during microsporogenesis and embryogenesis seems to be a general character of various seed protein genes.

Cloning and computer analysis of the promoter region of the legumin-like storage protein gene from buckwheat, Fagopyrum esculentum Moench

Using the modified 5?-RACE approach, a fragment containing the 955 bp long 5?- regulatory region of the buckwheat storage globulin gene (FeLEG1) has been amplified from the genomic DNA of buckwheat. The entire fragment was sequenced and the sequence analyzed by computer prediction of cis-regulatory elements possibly involved in tissue specific and developmentally controlled seed storage protein gene expression. The promoter obtained might be interesting not only for fundamental research, but also as a useful tool for biotechnological application.

Genomic organization and expression properties of the VfENOD5 gene from broad bean (Vicia faba L.)

A full-length cDNA encoding the broad bean (Vicia faba L.) early nodulin VfENOD5 was isolated from a nodule cDNA library. In addition to the ENOD5 homologues from other legumes the derived VfENOD5 amino acid sequence also displayed homologies to the phytocyanin-related nodulins GmENOD55-2, MtENOD16, and MtENOD20. A close inspection of the ENOD5 proteins from broad bean, pea and vetch indicated that all these nodulins possess a putative C-terminal GPI-anchor signal sequence. This novel finding supports the hypothesis that ENOD5 is an arabinogalactan protein. Tissue print hybridizations revealed that the broad bean ENOD5 gene was not only expressed in the central tissues of root nodules. In contrast to other legumes hybridizing transcripts were also be detected in a narrow zone within the peripheral nodule tissues. Sequence analysis of a genomic clone indicated the presence of a single intron interrupting the VfENOD5 coding region at a position precisely corresponding to the MtENOD16 and MtENOD20 introns.

Gene regulation during late embryogenesis: the RY motif of maturation-specific gene promoters is a direct target of the FUS3 gene product

The Arabidopsis mutants fus3 and abi3 show pleiotropic effects during embryogenesis including reduced levels of transcripts encoding embryo-specific seed proteins. To investigate the interaction between the B3-domain-containing transcription factors FUS3 and ABI3 with the RY cis-motif, conserved in many seed-specific promoters, a promoter analysis as well as band-shift experiments were performed. The analysis of promoter mutants revealed the structural requirements for the function of the RY cis-element. It is shown that both the nucleotide sequence and the alternation of purin and pyrimidin nucleotides (RY character) are essential for the activity of the motif. Further, it was shown that FUS3 and ABI3 can act independently of each other in controlling promoter activity and that the RY cis-motif is a target for both transcription factors. For FUS3, which is so far the smallest known member of the B3-domain family, a physical interaction with the RY motif was established. The functional and biochemical data demonstrate that the regulators FUS3 and ABI3 are essential components of a regulatory network acting in concert through the RY-promoter element to control gene expression during late embryogenesis and seed development.

Optimization of scFv antibody production in transgenic plants

BACKGROUND

Plants offer various advantages for the production of pharmaceutical proteins over conventional production systems such as bacterial or mammalian cell culture. In order to explore transgenic plants for large-scale production and storage of recombinant antibodies we tried to optimize the accumulation and stability of functionally active single chain Fv (scFv) antibodies in transgenic tobacco plants.

OBJECTIVES

Two different scFv antibodies which were expressed in different plant organs and plant cell compartments have been used for the study. Accumulation levels and antibody properties such as stability and antigen-binding activity were investigated.

STUDY DESIGN

For ubiquitous expression in tobacco plants, transcription of the scFv genes was controlled by the strong cauliflower mosaic virus (CaMV) 35S promoter. We used seed specific legumin B4 (LeB4) and the unknown seed protein (USP) promoters from Vicia faba for storage organ specific expression.

RESULTS

High accumulation of the two different scFv proteins in transgenic tobacco plants was only achieved by retention of the recombinant antibodies in the lumen of the endoplasmic reticulum (ER). Expression levels of scFv antibodies reached up to 4-6.8% of total soluble proteins (TSP) in leaves and up to 3-4% in ripe tobacco seeds. Transgenic tobacco seeds as well as tobacco leaves facilitated stable storage of ER-accumulated scFvs over an extended (seeds) or a short (leaves) period of time. Functionally active scFv proteins could be extracted after harvesting of the leaf material--drying and storage for 1 week at room temperature. Both the amount and the binding activity of the scFv proteins remained unchanged.

CONCLUSION

A plant expression system where the scFv-proteins are targeted in the ER provides not only the highest accumulation level of active single chain Fv antibodies ever reported but also a short- or long-term storage of the foreign protein in the harvested plant material.

Seed-specific immunomodulation of abscisic acid activity induces a developmental switch

A single-chain Fv antibody (scFv) gene, which has previously been used to immunomodulate abscisic acid (ABA) activity in transgenic tobacco to create a 'wilty' phenotype, was put under control of the seed-specific USP promoter from Vicia faba and used to transform tobacco. Transformants were phenotypically similar to wild-type plants apart from their seeds. Anti-ABA scFv embryo development differed markedly from wild-type embryo development. Seeds which accumulated similar levels of a scFv that binds to oxazolone, a hapten absent from plants, developed like wild-type embryos. Anti-ABA scFv embryos developed green cotyledons containing chloroplasts and accumulated photosynthetic pigments but produced less seed storage protein and oil bodies. Anti-ABA scFv seeds germinated precociously if removed from seed capsules during development but were incapable of germination after drying. Total ABA levels were higher than in wild-type seeds but calculated free ABA levels were near-zero until 21 days after pollination. We show for the first time seed-specific immunomodulation and the resulting switch from the seed maturation programme to a germination programme. We conclude that the immunomodulation of hormones can alter the development programme of target organs, allowing the study of the directly blocked endogenous molecules and manipulation of the system concerned.

Functional dissection of a napin gene promoter: identification of promoter elements required for embryo and endosperm-specific transcription

The promoter region (-309 to +44) of the Brassica napus storage protein gene napA was studied in transgenic tobacco by successive 5' as well as internal deletions fused to the reporter gene GUS (beta-glucuronidase). The expression in the two main tissues of the seed, the endosperm and the embryo, was shown to be differentially regulated. This tissue-specific regulation within the seed was found to affect the developmental expression during seed development. The region between -309 to -152, which has a large effect on quantitative expression, was shown to harbour four elements regulating embryo and one regulating endosperm expression. This region also displayed enhancer activity. Deletion of eight bp from position -152 to position -144 totally abolished the activity of the napA promoter. This deletion disrupted a cis element with similarity to an ABA-responsive element (ABRE) overlapping with an E-box, demonstrating its crucial importance for quantitative expression. An internal deletion of the region -133 to -120, resulted in increased activity in both leaves and endosperm and a decreased activity in the embryo. Within this region, a cis element similar to the (CA)n element, found in other storage protein promoters, was identified. This suggest that the (CA)n element is important for conferring seed specificity by serving both as an activator and a repressor element.

High-level production and long-term storage of engineered antibodies in transgenic tobacco seeds

We have used transgenic tobacco seeds to produce large amounts of a functionally active engineered antibody. A gene infusion encoding an antigen-binding single chain Fv protein (scFv) that recognizes the hapten oxazolone was constructed and used as a model. After characterization in a bacterial expression system ,the scFv gene was cloned into a plant expression cassette conferring seed specific expression, and transferred using Agrobacterium-mediated transformation, into Nicotiana tabacum. The expressed scFv could be detected in the developing as well as ripe seeds of regenerated transgenic plants, and the functionally active scFv is stabaly deposited and accumulates up to 0.67% of the total soluble seed protein. After storage of ripe transgenic tobacco seeds for one year at room temperature there was no loss of scFv protein or its antigen-binding activity.

Tissue-specific expression of an oat 12S seed globulin gene in developing tobacco seeds: differential mRNA and protein accumulation

We studied the expression of the oat globulin gene asglo5 in developing transgenic tobacco seeds. The asglo5 gene promoter directed transcription in the endosperm as well as in the provascular tissue, the presumptive root tip and the shoot apical meristem of the embryo as revealed by GUS reporter gene constructs and in situ hybridization. However, immunological tissue printing detected the oat protein exclusively in the tobacco endosperm, suggesting that extensive post-transcriptional regulatory processes influence the expression of the monocot transgene in the dicot host.

Differences in cell type-specific expression of the gene Opaque 2 in maize and transgenic tobacco

The Opaque 2 (O2) gene encodes a transcriptional activator of the basic region/leucine zipper family, which controls the synthesis of a major storage protein class in maize endosperm, the 22 kDa alpha-zeins, and of several other non-zein polypeptides including b32. We demonstrate, by analysing O2 mRNAs in different organs of maize plants, that the O2 gene is only active in the endosperm. Its transcription is precisely controlled during seed development: O2 mRNAs are first detected 10 days after pollination and accumulate in the endosperm over a period of 20 days. When introduced into tobacco plants, the O2 promoter directs the expression of the beta-glucuronidase (GUS) reporter gene in endosperm, but also in the embryo, cotyledons and pollen. The first 185 bp of the O2 promoter is sufficient for developmentally regulated expression in tobacco seeds. A distinct cis-acting element, located between positions -185 and -520, directs expression in the cotyledons of tobacco seedlings. The possible origins of this breakdown in promoter specificity in the heterologous host are discussed.

The glycinin box: a soybean embryo factor binding motif within the quantitative regulatory region of the 11S seed storage globulin promoter

The soybean embryo factor binding sequence in the glycinin A2B1a gene promoter was delimited to an A/T-rich 9 bp sequence, 5'-TAATAATTT-3', designated as the glycinin box, by DNA footprinting and gel mobility shift assay using synthetic oligonucleotides. It was shown that the interaction with the factor takes place at a defined DNA sequence rather than at random A/T-rich sequence blocks in the glycinin 5' flanking region. There are four glycinin boxes in the quantitative regulatory region between positions -545 and -378 of the glycinin A2B1a promoter. Multiple nonamer motifs similar to the glycinin box were also found in the equivalent regions of other glycinin and legumin promoters, suggesting that they must be conserved as a binding site for the embryo factor that activates the differential and stage-specific expression of seed 11S globulin genes in leguminous plants.

Regulation of an Arabidopsis oleosin gene promoter in transgenic Brassica napus

Progressive deletions of the 5'-flanking sequences of an Arabidopsis oleosin gene were fused to beta-glucuronidase (GUS) and introduced into Brassica napus plants using Agrobacterium-mediated transformation. The effect of these deletions on the quantitative level of gene expression, organ specificity and developmental regulation was assessed. In addition, the influence of abscisic acid (ABA), jasmonic acid (JA), sorbitol and a combined ABA/sorbitol treatment on gene expression was investigated. Sequences that positively regulate quantitative levels of gene expression are present between -1100 to -600 and -400 to -200 of the promoter. In addition, sequences present between -600 and -400 down-regulate quantitative levels of expression. In transgenic B. napus plants, the oleosin promoter directs seed-specific expression of GUS which is present at early stages of seed development and increases throughout seed maturation. Sequences present between -2500 and -1100 of the promoter are involved in modulating the levels of expression at early stages of embryo development. Histochemical staining of embryos demonstrated that expression is uniform throughout the tissues of the embryo. Sequences involved in the response to ABA and sorbitol are present between -400 and -200. The induction of GUS activity by a combined ABA/sorbitol treatment is additive suggesting that ABA is not the sole mediator of osmotically induced oleosin gene expression. A response to JA was only observed when the oleosin promoter was truncated to -600 suggesting that the reported effect of JA on oleosin gene expression may be at a post-transcriptional level.

A chimeric gene encoding the methionine-rich 2S albumin of the Brazil nut (Bertholletia excelsa H.B.K.) is stably expressed and inherited in transgenic grain legumes

The coding region of the 2S albumin gene of Brazil nut (Bertholletia excelsa H.B.K.) was completely synthesized, placed under control of the cauliflower mosaic virus (CaMV) 35S promoter and inserted into the binary vector plasmid pGSGLUC1, thus giving rise to pGSGLUC1-2S. This was used for transformation of tobacco (Nicotiana tabacum L. cv. Petit Havanna) and of the grain legume Vicia narbonensis L., mediated by the supervirulent Agrobacterium tumefaciens strain EHA 101. Putative transformants were selected by screening for neomycin phosphotransferase (NPT II) and beta-glucuronidase (GUS) activities. Transgenic plants were grown until flowering and fruiting occurred. The presence of the foreign gene was confirmed by Southern analysis. GUS activity was found in all organs of the regenerated transgenic tobacco and legume plants, including the seeds. In the legume, the highest expression levels of the CaMV 35S promoter-controlled 2S albumin gene were observed in leaves and roots. 2S albumin was localized in the vacuoles of leaf mesophyll cells of transgenic tobacco. The Brazil nut protein was present in the 2S fraction after gel filtration chromatography of the legume seed proteins and could be clearly identified by immunoblotting. Analysis of seeds from the R2 progenies of the legume and of transgenic tobacco plants revealed Mendelian inheritance of the foreign gene. Agrobacterium rhizogenes strain RifR 15834 harbouring the binary vector pGSGLUC1-2S was also used to transform Pisum sativum L. and Vicia faba L. Hairy roots expressed the 2S albumin-specific gene. Several shoots were raised but they never completely rooted and no fertile plants were obtained from these transformants.

Tissue-specific and temporal regulation of a beta-conglycinin gene: roles of the RY repeat and other cis-acting elements

Upstream regulatory sequences (URS) of the gene that encodes the alpha' subunit of beta-conglycinin, the 7S soybean seed storage protein, includes two RY repeat elements. The role of RY elements and sequences that bind soybean embryo factors 3 and 4 (SEF3 and SEF4; Allen et al., Plant Cell 1 (1989) 623-631) in regulating expression of the promoter was studied following site directed mutagenesis. Specific mutations introduced into these sequences abolished the in vitro binding activities of SEF3 and SEF4. The biological activities resulting from the mutations were determined in transgenic plants using two chimeric promoters comprising sequences from the CaMV 35S promoter and the alpha' subunit promoter. The uidA reporter gene was used to assess the levels of gene expression in transgenic plants. The mutations in the RY element and SEF3 and SEF4 binding sites had little effect on expression of the alpha' promoter. By contrast, mutations in the RY element had significant effect on gene expression when the URS from the alpha' promoter was ligated upstream of the core 35S promoter. Mutations in the RY element abolished the seed specific enhancing activity of the alpha' URS and caused expression of the chimeric promoter in leaves. These results indicate that the RY element plays a key role in seed-specific gene regulation in coordination with other cis-acting elements.

In situ localization of faba bean and oat legumin-type proteins in transgenic tobacco seeds by a highly sensitive immunological tissue print technique

We have used a highly sensitive immunological tissue print technique to study cell- and tissue-specific expression of heterologous genes in transgenic plants. Primary polyclonal antibodies, raised against legumin of faba bean (Vicia faba L.) and 12S globulin of oat (Avena sativa L.) were used to localize these proteins in transgenic tobacco seeds in a streptavidin-alkaline phosphatase assay in combination with biotinylated secondary antibodies producing a higher sensitivity (by several amplification steps) of the assay. Both storage protein genes were found to be expressed in a specific pattern. While legumin is preferentially accumulated in certain parts of the embryo, the oat legumin-type globulin is restricted to the endosperm. The applied technique is highly sensitive with a resolution power down to the single-cell level and allows rapid screening of large numbers of samples.

A complex ensemble of cis-regulatory elements controls the expression of a Vicia faba non-storage seed protein gene

We have identified cis-regulatory elements within the 5'-upstream region of a Vicia faba non-storage seed protein gene, called usp, by studying the expression of usp-promoter deletion fragments fused to reporter genes in transgenic tobacco seeds. 0.4 kb of usp upstream sequence contain at least six, but probably more, distinct cis-regulatory elements which are responsible for seemingly all quantitative, spatial and temporal aspects of expression. Expression-increasing and -decreasing elements are interspersed and include an AT-rich sequence, a G-box element and a CATGCATG motif. The latter acts as a negative element in contrast to what has been found for the same motif in legumin- and vicilin-type seed storage protein gene promoters. Seed specificity of expression is mainly determined by the -68/+51 region which confers, however, only very low levels of expression. The data support the combinatorial model of promoter function.

An SAR sequence containing 395 bp DNA fragment mediates enhanced, gene-dosage-correlated expression of a chimaeric heat shock gene in transgenic tobacco plants

A 395 bp fragment located downstream from the soybean heat shock gene Gmhsp 17.6-L exhibits several characteristics of scaffold attachment region (SAR) sequences. It contains matrix consensus elements, a topoisomerase II binding sequence and it associates with the isolated nuclear scaffold of soybean in vitro. Chimaeric genes containing the SARL fragment either at one side (5' or 3') or at both sides of a heat shock promoter-regulated beta-glucuronidase reporter gene were constructed. A five- to nine-fold increase of heat-inducible beta-glucuronidase activity was observed in transgenic tobacco plants containing constructs with SARL fragments either at both sides or with at least one SARL copy located upstream from the reporter gene. The gene copy number is positively correlated with the level of heat-inducible reporter gene activity in these plants but positional effects are not entirely eliminated. Thus, SAR sequences may potentially be used to increase gene expression, via as yet unknown mechanisms, and to reduce adverse effects on the expression of multiple gene copies in transgenic plants.

cis-acting regulatory regions of the soybean seed storage 11S globulin gene and their interactions with seed embryo factors

A 2.2 kb fragment containing the 5'-flanking region of the soybean glycinin A2B1a gene and its successive deletions with a shorter 5'-flanking sequence were fused, in frame, to the beta-glucuronidase (GUS) reporter gene. The resultant fusions were introduced into tobacco plants via Agrobacterium tumefaciens. Assays of the GUS activity in seeds of transgenic tobacco showed that the upstream region, -657 to -327 (relative to the transcription initiation site [+1]), of the glycinin gene is required for optimal expression of the transformed gene. Interactions between embryo nuclear factors and DNA fragments covering the downstream region of -326, in which are included the TATA box and legumin boxes, were not apparent. The embryo factors capable of binding specifically to three subregions, -653 to -527, -526 to -422, and -427 to -321, of the upstream regulatory region were detected. Such factors appeared to be organ-specific and could be found solely in developing seeds at the early middle stage of embryogenesis (around 24 days after flowering). Evidence obtained by characterizing the nature of the binding proteins and by gel mobility shift assays established that the same factor does interact with a consensus motif 5'-ATA/TATTTCN-/CTA-3' which occurs four times in the cis-acting regulatory region between -657 and -327. Moreover, this conserved motif could also be found in the 5' regulatory region of another glycinin A1aB1b gene. Thus it is likely that the observed interaction between the nuclear factor and the conserved motifs would lead to activation of transcription from the glycinin genes in maturing soybean seeds.

Differential manifestation of seed mortality induced by seed-specific expression of the gene for diphtheria toxin A chain in Arabidopsis and tobacco

A pea vicilin promoter-diphtheria toxin A (DTx-A) chain gene fusion was introduced into Arabidopsis and tobacco. The chimeric Dtx-A gene behaves as a dominant, seed-lethal, Mendelian factor, and the segregation ratios are consistent with the numbers of integrated copies as revealed by Southern blotting. Germination deficiency results from distinct developmental abnormalities, thus allowing genetic dissection of seed development. The endosperm is affected first in both species. In Arabidopsis, full cellularization of the initially syncytial endosperm does not take place, which results in shrinkage and a shriveled appearance of the mature dry seed. The embryo, which appears structurally normal and lacks visible lesions, ceases to develop at the partially recurved cotyledon stage and does not use the remaining endosperm. In tobacco, peripheral degeneration and premature termination of cellular endosperm development occurs at the cotyledon initiation stage. Lesions appear in the cotyledons at the advanced cotyledon stage, but the embryo continues to grow and attains nearly the same size and level of differentiation as mature wild-type embryos before degeneration and intracellular disintegration take place throughout. Accumulation of protein bodies and other cytoplasmic inclusions is very limited and occurs only in few cells. The timing and distribution of lesions follow a pattern typical for accumulation of protein bodies in wild-type seeds. These observations are consistent with expression of the vicilin promoter in the enlargement phase of cell differentiation. A novel tissue interaction arises, when the embryo uses up all the arrested endosperm: the embryo proves to be capable of absorbing the parenchyma layers of the integument, which are normally obliterated by, and incorporated into, the endosperm.(ABSTRACT TRUNCATED AT 250 WORDS)

The legumin boxes and the 3' part of a soybean beta-conglycinin promoter are involved in seed gene expression in transgenic tobacco plants

beta-conglycinin is one of the major seed storage proteins in soybean. It is composed of three subunits, namely alpha, alpha' and beta. The expression of beta-conglycinin is highly regulated, being restricted to the embryo during the mid-maturation phase of embryogeny. Two series of constructs were made with the alpha' subunit promoter and the GUS reporter gene to investigate the cis-acting elements involved in the regulated expression of this promoter. The activity of each construct was tested in transgenic tobacco plants. In the first series of constructs, we checked if the 'legumin box', a sequence found in most legume seed storage protein genes as well as in other seed-specific genes, is involved in the regulated expression of the alpha' subunit of the beta-conglycinin gene in tobacco. To this end, both copies of the alpha' subunit promoter legumin boxes were mutagenized in vitro. The transcriptional activity of the single mutants and the double mutant were compared with that of the wild-type promoter. Our results show that the legumin boxes act together to increase transcription of the beta-conglycinin alpha' subunit gene by about a factor of ten. This is the first demonstration of a function for the legumin box in transcriptional regulation. In the second series of experiments, we wished to determine if the 3' part of the promoter (the CCAAT and TATAA region) contains important regulatory elements. We found that this small fragment (-82 to +13 bp) can confer by itself a low level of seed-specific gene expression. Chimaeric promoters constructed from parts of the alpha' subunit promoter and of the constitutive CaMV 35S promoter were also analysed. These constructs also revealed the importance of the CCAAT and TATAA region of the alpha' subunit promoter in seed-specific gene expression.

Direct screening for high-level expression of an introduced alpha-amylase gene in plants

A method is described for obtaining transgenic plants with a high level of expression of the introduced gene. Tobacco protoplasts were transformed with an expression construct containing a translational fusion between mature alpha-amylase from Bacillus licheniformis and the signal peptide of the tobacco PR-S protein. A total number of 5200 transformed protoplasts was cultured to microcalli and screened for alpha-amylase expression by incubation on media containing starch followed by staining with iodine. The calli were divided into four classes, based on the resulting halo sizes on the plates. The halo sizes were found to correlate with the expression levels in transgenic plants regenerated from the calli. The expression levels varied between 0 and 0.5% of soluble leaf protein in the regenerated transgenic plants. Wider implications of this method are discussed.