A novel seed protein gene from Vicia faba is developmentally regulated in transgenic tobacco and Arabidopsis plants

Cre-mediated autoexcision of selectable marker genes in soybean, cotton, canola and maize transgenic plants

Efficient selectable marker gene autoexcision in transgenic plants of soybean, cotton, canola, and maize is achieved by effective Cre recombinase expression. Selectable marker genes are often required for efficient generation of transgenic plants in plant transformation but are not desired once the transgenic events are obtained. We have developed Cre/loxP autoexcision systems to remove selectable marker genes in soybean, cotton, canola and maize. We tested a set of vectors with diverse promoters and identified promising promoters to drive cre expression for each of the four crops. We evaluated both the efficiency of generating primary transgenic events with low transgene copy numbers, and the frequency of marker-free progeny in the next generation. The best performing vectors gave no obvious decrease in the transformation frequency in each crop and generated homozygous marker-free progeny in the next generation. We found that effective expression of Cre recombinase for marker gene autoexcision can be species dependent. Among the vectors tested, the best autoexcision frequency (41%) in soybean transformation came from using the soybean RSP1 promoter for cre expression. The cre gene expressed by soybean RSP1 promoter with an Arabidopsis AtpE intron delivered the best autoexcision frequency (69%) in cotton transformation. The cre gene expressed by the embryo-specific eUSP88 promoter from Vicia faba conferred the best marker excision frequency (32%) in canola transformation. Finally, the cre gene expressed by the rice CDC45-1 promoter resulted in 44% autoexcision in maize transformation. The Cre/loxP recombinase system enables the generation of selectable marker-free transgenic plants for commercial product development in four agriculturally important crops and provides further improvement opportunities for more specific and better marker excision efficiency.

Arabidopsis ETHYLENE INSENSITIVE 3 directly regulates the expression of PG1β-like family genes in response to aluminum stress

The genes in the subfamily PG1β (beta subunit of poly-galacturonase isoenzyme 1) have a clear effect on the biosynthesis pathway of pectin, a main component of the cell wall. However, the detailed functions of the PG1β-like gene members in Arabidopsis (AtPG1-3) have not yet been determined. In this study, we investigated their functional roles in response to aluminum (Al) stress. Our results indicate that the PG1β-like gene members are indeed involved in the Al-stress response and they can modulate its accumulation in roots to achieve optimum root elongation and hence better seedling growth. We found that transcription factor EIN3 (ETHYLENE INSENSITIVE 3) alters pectin metabolism and the EIN3 gene responds to Al stress to affect the pectin content in the root cell walls, leading to exacerbation of the inhibition of root growth, as reflected by the phenotypes of overexpressing lines. We determined that EIN3 can directly bind to the promoter regions of PG1-3, which act downstream of EIN3. Thus, our results show that EIN3 responds to Al stress in Arabidopsis directly through regulating the expression of PG1-3. Hence, EIN3 mediates their functions by acting as a biomarker in their molecular biosynthesis pathways, and consequently orchestrates their biological network in response to Al stress.

Set up from the beginning: The origin and early development of cassava storage roots

Despite the importance of storage root (SR) organs for cassava and the other root crops yield, their developmental origin is poorly understood. Here we use multiple approaches to shed light on the initial stages of root development demonstrating that SR and fibrous roots (FR) follow different rhizogenic processes. Transcriptome analysis carried out on roots collected before, during and after root bulking highlighted early and specific activation of a number of functions essential for root swelling and identified root-specific genes able to effectively discriminate emerging FR and SR. Starch and sugars start to accumulate at a higher rate in SR before they swell but only after parenchyma tissue has been produced. Finally, using non-destructive computed tomography measurements, we show that SR (but not FR) contain, since their emergence from the stem, an inner channel structure in continuity with the stem secondary xylem, indicating that SR derive from a distinct rhizogenic process compared with FR.

Improving seed germination and oil contents by regulating the GDSL transcriptional level in Brassica napus

Seed germination rate and oil content can be regulated at theGDSL transcriptional level by eitherAtGDSL1 orBnGDSL1 inB. napus. Gly-Asp-Ser-Leu (GDSL)-motif lipases represent an important subfamily of lipolytic enzymes, which play important roles in lipid metabolism, seed development, abiotic stress, and pathogen defense. In the present study, two closely related GDSL-motif lipases, Brassica napus GDSL1 and Arabidopsis thaliana GDSL1, were characterized as functioning in regulating germination rate and seed oil content in B. napus. AtGDSL1 and BnGDSL1 overexpression lines showed an increased seed germination rate and improved seedling establishment compared with wild type. Meanwhile, the constitutive overexpression of AtGDSL1 and BnGDSL1 promoted lipid catabolism and decreased the seed oil content. While RNAi-mediated suppression of BnGDSL1 (Bngdsl1) in B. napus improved the seed oil content and decreased seed germination rate. Moreover, the Bngdsl1 transgenic seeds showed changes in the fatty acid (FA) composition, featuring an increase in C18:1 and a decrease in C18:2 and C18:3. The transcriptional levels of six related core enzymes involved in FA mobilization were all elevated in the AtGDSL1 and BnGDSL1 overexpression lines, but strongly suppressed in the Bngdsl1 transgenic line. These results suggest that improving the seed germination and seed oil content in B. napus could be achieved by regulating the GDSL transcriptional level.

An endoplasmic reticulum-localized Coffea arabica BURP domain-containing protein affects the response of transgenic Arabidopsis plants to diverse abiotic stresses

The Coffea arabica BURP domain-containing gene plays an important role in the response of transgenic Arabidopsis plants to abiotic stresses via regulating the level of diverse proteins. Although the functions of plant-specific BURP domain-containing proteins (BDP) have been determined for a few plants, their roles in the growth, development, and stress responses of most plant species, including coffee plant (Coffea arabica), are largely unknown. In this study, the function of a C. arabica BDP, designated CaBDP1, was investigated in transgenic Arabidopsis plants. The expression of CaBDP1 was highly modulated in coffee plants subjected to drought, cold, salt, or ABA. Confocal analysis of CaBDP1-GFP fusion proteins revealed that CaBDP1 is localized in the endoplasmic reticulum. The ectopic expression of CaBDP1 in Arabidopsis resulted in delayed germination of the transgenic plants under abiotic stress and in the presence of ABA. Cotyledon greening and seedling growth of the transgenic plants were inhibited in the presence of ABA due to the upregulation of ABA signaling-related genes like ABI3, ABI4, and ABI5. Proteome analysis revealed that the levels of several proteins are modulated in CaBDP1-expressing transgenic plants. The results of this study underscore the importance of BURP domain proteins in plant responses to diverse abiotic stresses.

Seed-Specific Expression of Spider Silk Protein Multimers Causes Long-Term Stability

Seeds enable plants to germinate and to grow in situations of limited availability of nutrients. The stable storage of different seed proteins is a remarkable presumption for successful germination and growth. These strategies have been adapted and used in several molecular farming projects. In this study, we explore the benefits of seed-based expression to produce the high molecular weight spider silk protein FLAG using intein-based trans-splicing. Multimers larger than 460 kDa in size are routinely produced, which is above the native size of the FLAG protein. The storage of seeds for 8 weeks and 1 year at an ambient temperature of 15°C does not influence the accumulation level. Even the extended storage time does not influence the typical pattern of multimerized bands. These results show that seeds are the method of choice for stable accumulation of products of complex transgenes and have the capability for long-term storage at moderate conditions, an important feature for the development of suitable downstream processes.

Isolation of a maize ZmCI-1B promoter and characterization of its activity in transgenic maize and tobacco

KEY MESSAGE

The 2-kb ZmCI - 1B promoter is active in the root and embryo and induced by wounding in maize and the 220-bp 5'-deleted segment maybe the minimal promoter. The subtilisin-chymotrypsin inhibitor gene, CI-1B of Zea mays (ZmCI-1B), has been suggested to induce the maize defense system to resist insect attack. Real-time RT-PCR showed that ZmCI-1B gene exhibited especially high expression in roots and embryos. The 2-kb full-length promoter of ZmCI-1B gene was isolated from the maize genome and used to drive expression of a beta-glucuronidase (GUS) reporter gene for transient expression and stable expression analysis in maize. The results of GUS histochemical staining in transgenic maize plants revealed that the ZmCI-1B promoter induced GUS expression preferentially in roots and embryos and in response to wounding. A series of 5'-deleted segments of the ZmCI-1B promoter were cloned individually to drive GUS expression for further analysis. Deletion analysis combined with the histochemical staining of transgenic tobacco plants revealed 220-bp segment could drive GUS in a tissue-specific and wounding-induced expression in tobacco; thus, it maybe the minimally active promoter of ZmCI-1B gene. Furthermore, it revealed that the ZmCI-1B promoter contained tissue-specific and wounding-induced elements.

Inspection of the grapevine BURP superfamily highlights an expansion of RD22 genes with distinctive expression features in berry development and ABA-mediated stress responses

The RESPONSIVE TO DEHYDRATION 22 (RD22) gene is a molecular link between abscisic acid (ABA) signalling and abiotic stress responses. Its expression has been used as a reliable ABA early response marker. In Arabidopsis, the single copy RD22 gene possesses a BURP domain also located at the C-terminus of USP embryonic proteins and the beta subunit of polygalacturonases. In grapevine, a RD22 gene has been identified but putative paralogs are also found in the grape genome, possibly forming a large RD22 family in this species. In this work, we searched for annotations containing BURP domains in the Vitis vinifera genome. Nineteen proteins were defined by a comparative analysis between the two genome predictions and RNA-Seq data. These sequences were compared to other plant BURPs identified in previous genome surveys allowing us to reconceive group classifications based on phylogenetic relationships and protein motif occurrence. We observed a lineage-specific evolution of the RD22 family, with the biggest expansion in grapevine and poplar. In contrast, rice, sorghum and maize presented highly expanded monocot-specific groups. The Vitis RD22 group may have expanded from segmental duplications as most of its members are confined to a region in chromosome 4. The inspection of transcriptomic data revealed variable expression of BURP genes in vegetative and reproductive organs. Many genes were induced in specific tissues or by abiotic and biotic stresses. Three RD22 genes were further studied showing that they responded oppositely to ABA and to stress conditions. Our results show that the inclusion of RNA-Seq data is essential while describing gene families and improving gene annotations. Robust phylogenetic analyses including all BURP members from other sequenced species helped us redefine previous relationships that were erroneously established. This work provides additional evidence for RD22 genes serving as marker genes for different organs or stresses in grapevine.

AtRD22 and AtUSPL1, members of the plant-specific BURP domain family involved in Arabidopsis thaliana drought tolerance

Crop plants are regularly challenged by a range of environmental stresses which typically retard their growth and ultimately compromise economic yield. The stress response involves the reprogramming of approximately 4% of the transcriptome. Here, the behavior of AtRD22 and AtUSPL1, both members of the Arabidopsis thaliana BURP (BNM2, USP, RD22 and polygalacturonase isozyme) domain-containing gene family, has been characterized. Both genes are up-regulated as part of the abscisic acid (ABA) mediated moisture stress response. While AtRD22 transcript was largely restricted to the leaf, that of AtUSPL1 was more prevalent in the root. As the loss of function of either gene increased the plant's moisture stress tolerance, the implication was that their products act to suppress the drought stress response. In addition to the known involvement of AtUSPL1 in seed development, a further role in stress tolerance was demonstrated. Based on transcriptomic data and phenotype we concluded that the enhanced moisture stress tolerance of the two loss-of-function mutants is a consequence of an enhanced basal defense response.

Loss of cytosolic phosphoglucose isomerase affects carbohydrate metabolism in leaves and is essential for fertility of Arabidopsis

Carbohydrate metabolism in plants is tightly linked to photosynthesis and is essential for energy and carbon skeleton supply of the entire organism. Thus, the hexose phosphate pools of the cytosol and the chloroplast represent important metabolic resources that are maintained through action of phosphoglucose isomerase (PGI) and phosphoglucose mutase interconverting glucose 6-phosphate, fructose 6-phosphate, and glucose 1-phosphate. Here, we investigated the impact of disrupted cytosolic PGI (cPGI) function on plant viability and metabolism. Overexpressing an artificial microRNA targeted against cPGI (amiR-cpgi) resulted in adult plants with vegetative tissue essentially free of cPGI activity. These plants displayed diminished growth compared with the wild type and accumulated excess starch in chloroplasts but maintained low sucrose content in leaves at the end of the night. Moreover, amiR-cpgi plants exhibited increased nonphotochemical chlorophyll a quenching during photosynthesis. In contrast to amiR-cpgi plants, viable transfer DNA insertion mutants disrupted in cPGI function could only be identified as heterozygous individuals. However, homozygous transfer DNA insertion mutants could be isolated among plants ectopically expressing cPGI. Intriguingly, these plants were only fertile when expression was driven by the ubiquitin10 promoter but sterile when the seed-specific unknown seed protein promoter or the Cauliflower mosaic virus 35S promoter were employed. These data show that metabolism is apparently able to compensate for missing cPGI activity in adult amiR-cpgi plants and indicate an essential function for cPGI in plant reproduction. Moreover, our data suggest a feedback regulation in amiR-cpgi plants that fine-tunes cytosolic sucrose metabolism with plastidic starch turnover.

A Vigna radiata 8S globulin α' promoter drives efficient expression of GUS in Arabidopsis cotyledonary embryos

Plants are proven effective bioreactors for the production of heterologous proteins including those desired by the biopharmaceutical industry. However, the potential of plants as bioreactors is limited by the availability of characterized plant promoters that can drive target gene expression in relatively distant plant species. Seeds are ideal for protein storage because seed proteins can be kept stably for several months. Hence, a strong promoter that can direct the expression and accumulation of target proteins within seeds represents a powerful tool in plant biotechnology. Toward this end, an effort was made to identify such a promoter from Vigna radiata (mung bean) to drive expression in dicot seeds. A 784-bp 5'-flanking sequence of the gene encoding the 8S globulin α' subunit (8SGα') of the V. radiata seed storage protein was isolated by genome walking. When the 5'-flanking region was analyzed with bioinformatics tools, numerous putative cis-elements were identified. The Green Fluorescent Protein (GFP) regulated by this promoter was observed to be transiently expressed in protoplasts derived from V. radiata cotyledons. Finally, transgenic Arabidopsis plants expressing the β-glucuronidase (GUS) reporter gene driven from the 8S globulin α' promoter showed strong GUS expression in transgenic embryos in both histochemical and quantitative GUS assays, confirming high expression within seeds. Therefore, the V. radiata 8S α' promoter has shown potential in directing expression in seeds for bioreactor applications.

Reconstitution of EPA and DHA biosynthesis in arabidopsis: iterative metabolic engineering for the synthesis of n-3 LC-PUFAs in transgenic plants

An iterative approach to optimising the accumulation of non-native long chain polyunsaturated fatty acids in transgenic plants was undertaken in Arabidopsis thaliana. The contribution of a number of different transgene enzyme activities was systematically determined, as was the contribution of endogenous fatty acid metabolism. Successive iterations were informed by lipidomic analysis of neutral, polar and acyl-CoA pools. This approach allowed for a four-fold improvement on levels previously reported for the accumulation of eicosapentaenoic acid in Arabidopsis seeds and also facilitated the successful engineering of the high value polyunsaturated fatty acid docosahexaenoic acid to 10-fold higher levels. Our studies identify the minimal gene set required to direct the efficient synthesis of these fatty acids in transgenic seed oil.

Suppression of the SUGAR-DEPENDENT1 triacylglycerol lipase family during seed development enhances oil yield in oilseed rape (Brassica napus L.)

Increasing the productivity of oilseed crops is an important challenge for plant breeders and biotechnologists. To date, attempts to increase oil production in seeds via metabolic pathway engineering have focused on boosting synthetic capacity. However, in the tissues of many organisms, it is well established that oil levels are determined by both anabolism and catabolism. Indeed, the oil content of rapeseed (Brassica napus L.) has been reported to decline by approximately 10% in the final stage of development, as the seeds desiccate. Here, we show that RNAi suppression of the SUGAR-DEPENDENT1 triacylglycerol lipase gene family during seed development results in up to an 8% gain in oil yield on either a seed, plant or unit area basis in the greenhouse, with very little adverse impact on seed vigour. Suppression of lipolysis could therefore constitute a new method for enhancing oil yield in oilseed crops.

Influence of elastin-like peptide fusions on the quantity and quality of a tobacco-derived human immunodeficiency virus-neutralizing antibody

The use of vaginal microbicides containing human immunodeficiency virus (HIV)-neutralizing antibodies (nAbs) is a promising strategy to prevent HIV-1 infection. Although antibodies are predominantly manufactured using mammalian cells, elastin-like peptide (ELP) fusion technology improves the stability of recombinant, plant-produced proteins and facilitates their purification, making plants an alternative platform for antibody production. We generated transgenic tobacco plants accumulating four different formats of the anti-HIV-1 antibody 2G12 in the endoplasmic reticulum (ER), i.e. with ELP on either the light or heavy chain, on both, or on neither. Detailed analysis of affinity-purified antibodies by surface plasmon resonance spectroscopy showed that the kinetic binding parameters of all formats were identical to 2G12 lacking ELP produced in Chinese hamster ovary (CHO) cells. Importantly, protein purification from seeds by inverse transition cycling (ITC) did not affect the binding kinetics. Analysis of heavy chain N-glycans from leaf-derived antibodies showed that retrieval to the ER was efficient for all formats. In seeds, however, N-glycans on the naked antibody were extensively trimmed compared with those on the ELP fusion formats, and were localized to a different subcellular compartment. The in vitro HIV-neutralization properties of the tobacco-derived 2G12 were equivalent to or better than those of the CHO counterpart.

Protein storage vacuoles of Brassica napus zygotic embryos accumulate a BURP domain protein and perturbation of its production distorts the PSV

BNM2is a prototypical member of the enigmatic BURP domain protein family whose members contain the signature FX6-7GX10-28PX25-31CX11-12X2SX45-56CHX10 CHX25-29CHX2TX15-16PX5CH in the C-terminus. This protein family occurs only in plants, and the cognate genes vary very widely in their expression contexts in vegetative and reproductive tissues. None of theBURP family members has been assigned any biochemical function. BNM2 was originally discovered as a gene expressed in microspore derived embryos (MDE) of Brassica napus but we found that MDE do not contain the corresponding protein. We show that BNM2 protein production is confined to the seeds and localized to the protein storage vacuoles (PSV) even though the transcript is found in vegetative parts and floral buds as well. In developing seeds, transcript accumulation precedes protein appearance by more than 18 days. RNA accumulation peaks at approximately 20 days post anthesis (DPA) whereas protein accumulation reaches its maximum at approximately 40 DPA. Transgenic expression of BNM2 does not abrogate this regulation to yield ectopic protein production or to alter the temporal aspect ofBNM2 accumulation. Overexpression ofBNM2 led to spatial distortion of storage protein accumulation within PSV and to some morphological alterations of PSVs. However, the overall storage protein content was not altered.

The BURP domain protein AtUSPL1 of Arabidopsis thaliana is destined to the protein storage vacuoles and overexpression of the cognate gene distorts seed development

BURP domain proteins comprise a broadly distributed, plant-specific family of functionally poorly understood proteins. VfUSP (Vicia faba Unknown Seed Protein) is the founding member of this family. The BURP proteins are characterized by a highly conserved C-terminal protein domain with a characteristic cysteine-histidine pattern. The Arabidopsis genome contains five BURP-domain encoding genes. Three of them are similar to the non-catalytic beta-subunit of the polygalacturonase of tomato and form a distinct subgroup. The remaining two genes are AtRD22 and AtUSPL1. The deduced product of AtUSPL1 is similar in size and sequence to VfUSP and that of the Brassica napus BNM2 gene which is expressed during microspore-derived embryogenesis. The protein products of BURP genes have not been found, especially that of VfUSP despite a great deal of interest arising from copious transcription of the gene in seeds. Here, we demonstrate that VfUSP and AtUSPL1 occur in cellular compartments essential for seed protein synthesis and storage, like the Golgi cisternae, dense vesicles, prevaculoar vesicles and the protein storage vacuoles in the parenchyma cells of cotyledons. Ectopic expression of AtUSPL1 leads to a shrunken seed phenotype; these seeds show structural alterations in their protein storage vacuoles and lipid vesicles. Furthermore, there is a reduction in the storage protein content and a perturbation in the seed fatty acid composition. However, loss of AtUSP1 gene function due to T-DNA insertions does not lead to a phenotypic change under laboratory conditions even though the seeds have less storage proteins. Thus, USP is pertinent to seed development but its role is likely shared by other proteins that function well enough under the laboratory growth conditions.

Antibody expressing pea seeds as fodder for prevention of gastrointestinal parasitic infections in chickens

BACKGROUND

Coccidiosis caused by protozoans of genus Eimeria is a chicken parasitic disease of great economical importance. Conventional disease control strategies depend on vaccination and prophylactic use of anticoccidial drugs. Alternative solution to prevent and treat coccidiosis could be provided by passive immunization using orally delivered neutralizing antibodies. We investigated the possibility to mitigate the parasitic infection by feeding poultry with antibody expressing transgenic crop seeds.

RESULTS

Using the phage display antibody library, we generated a panel of anti-Eimeria scFv antibody fragments with high sporozoite-neutralizing activity. These antibodies were expressed either transiently in agrobacteria-infiltrated tobacco leaves or stably in seeds of transgenic pea plants. Comparison of the scFv antibodies purified either from tobacco leaves or from the pea seeds demonstrated no difference in their antigen-binding activity and molecular form compositions. Force-feeding experiments demonstrated that oral delivery of flour prepared from the transgenic pea seeds had higher parasite neutralizing activity in vivo than the purified antibody fragments isolated from tobacco. The pea seed content was found to protect antibodies against degradation by gastrointestinal proteases (>100-fold gain in stability). Ad libitum feeding of chickens demonstrated that the transgenic seeds were well consumed and not shunned. Furthermore, feeding poultry with shred prepared from the antibody expressing pea seeds led to significant mitigation of infection caused both by high and low challenge doses of Eimeria oocysts.

CONCLUSION

The results suggest that our strategy offers a general approach to control parasitic infections in production animals using cost-effective antibody expression in crop seeds affordable for the animal health market.

The synthesis and accumulation of stearidonic acid in transgenic plants: a novel source of 'heart-healthy' omega-3 fatty acids

Dietary omega-3 polyunsaturated fatty acids have a proven role in reducing the risk of cardiovascular disease and precursor disease states such as metabolic syndrome. Although most studies have focussed on the predominant omega-3 fatty acids found in fish oils (eicosapentaenoic acid and docosahexaenoic acid), recent evidence suggests similar health benefits from their common precursor, stearidonic acid. Stearidonic acid is a Delta6-unsaturated C18 omega-3 fatty acid present in a few plant species (mainly the Boraginaceae and Primulaceae) reflecting the general absence of Delta6-desaturation from higher plants. Using a Delta6-desaturase from Primula vialii, we generated transgenic Arabidopsis and linseed lines accumulating stearidonic acid in their seed lipids. Significantly, the P. vialiiDelta6-desaturase specifically only utilises alpha-linolenic acid as a substrate, resulting in the accumulation of stearidonic acid but not omega-6 gamma-linolenic acid. Detailed lipid analysis revealed the accumulation of stearidonic acid in neutral lipids such as triacylglycerol but an absence from the acyl-CoA pool. In the case of linseed, the achieved levels of stearidonic acid (13.4% of triacylglycerols) are very similar to those found in the sole natural commercial plant source (Echium spp.) or transgenic soybean oil. However, both those latter oils contain gamma-linolenic acid, which is not normally present in fish oils and considered undesirable for heart-healthy applications. By contrast, the stearidonic acid-enriched linseed oil is essentially devoid of this fatty acid. Moreover, the overall omega-3/omega-6 ratio for this modified linseed oil is also significantly higher. Thus, this nutritionally enhanced linseed oil may have superior health-beneficial properties.

Genome-wide identification of BURP domain-containing genes in rice reveals a gene family with diverse structures and responses to abiotic stresses

Increasing evidence suggests that a gene family encoding proteins containing BURP domains have diverse functions in plants, but systematic characterization of this gene family have not been reported. In this study, 17 BURP family genes (OsBURP01-17) were identified and analyzed in rice (Oryza sativa L.). These genes have diverse exon-intron structures and distinct organization of putative motifs. Based on the phylogenetic analysis of BURP protein sequences from rice and other plant species, the BURP family was classified into seven subfamilies, including two subfamilies (BURP V and BURP VI) with members from rice only and one subfamily (BURP VII) with members from monocotyledons only. Two BURP gene clusters, belonging to BURP V and BURP VI, were located in the duplicated region on chromosome 5 and 6 of rice, respectively. Transcript level analysis of BURP genes of rice in various tissues and organs revealed different tempo-spatial expression patterns, suggesting that these genes may function at different stages of plant growth and development. Interestingly, all the genes of the BURP VII subfamily were predominantly expressed in flower organs. We also investigated the expression patterns of BURP genes of rice under different stress conditions. The results suggested that, except for two genes (OsBURP01 and OsBURP13), all other members were induced by at least one of the stresses including drought, salt, cold, and abscisic acid treatment. Two genes (OsBURP05 and OsBURP16) were responsive to all the stress treatments and most of the OsBURP genes were responsive to salt stress. Promoter sequence analysis revealed an over-abundance of stress-related cis-elements in the stress-responsive genes. The data presented here provide important clues for elucidating the functions of genes of this family.

Interspecies compatibility of the anther specific cell wall invertase promoters from Arabidopsis and tobacco for generating male sterile plants

Histochemical GUS-staining and fluorometric analyses revealed strong tissue specific activities of the cell wall invertase promoters Nin88 from Nicotiana tabacum and AtcwINV2 from Arabidopsis thaliana that are restricted tightly to anthers and pollen, respectively. Both in A. thaliana and N. tabacum repression of invertase activity by anther specific RNA-interference turned out to be an efficient method to circumvent carbohydrate supply of the symplastically isolated pollen with subsequent strong decrease of pollen germination ability and seed setting. In the case of tobacco, comparable results were also obtained by expressing a proteinaceous invertase inhibitor, whereas this approach was less efficient in Arabidopis. The present study revealed that anther specific interference with invertase-activity in order to generate male sterile plants can be applied to members of the two different plant families Solanaceae (N. tabacum) and Brassicaceae (A. thalaina) and the strategy seems to be a general tool for practical application in hybrid breeding or as biological safety precautions. To elucidate the compatibility of the isolated promoters beyond plant families, we transferred the regulatory sequences into the respectively heterologous systems, i.e. the Nin88 promoter into Arabidopsis and the AtcwINV2 promoter into tobacco. The specificities of both promoters are maintained in the heterologous backgrounds, but their activities are strongly reduced as GUS-stainings of flowers and pollen revealed and fluorometrical quantification confirmed.

Transcriptional regulation of storage protein synthesis during dicotyledon seed filling

Seeds represent a major source of nutrients for human and animal livestock diets. The nutritive value of seeds is largely due to storage products which accumulate during a key phase of seed development, seed filling. In recent years, our understanding of the mechanisms regulating seed filling has advanced significantly due to the diversity of experimental approaches used. This review summarizes recent findings related to transcription factors that regulate seed storage protein accumulation. A framework for the regulation of storage protein synthesis is established which incorporates the events before, during and after seed storage protein synthesis. The transcriptional control of storage protein synthesis is accompanied by physiological and environmental controls, notably through the action of plant hormones and other intermediary metabolites. Finally, recent post-genomics analyses on different model plants have established the existence of a conserved seed filling process involving the master regulators (LEC1, LEC2, ABI3 and FUS3) but also revealed certain differences in fine regulation between plant families.

Metabolic engineering of omega3-very long chain polyunsaturated fatty acid production by an exclusively acyl-CoA-dependent pathway

omega3-Very long chain polyunsaturated fatty acids (VLCPUFA) are essential for human development and brain function and, thus, are indispensable components of the human diet. The current main source of VLCPUFAs is represented by ocean fish stocks, which are in severe decline, and the development of alternative, sustainable sources of VLCPUFAs is urgently required. Our research aims at exploiting the powerful infrastructure available for the large scale culture of oilseed crops, such as rapeseed, to produce VLCPUFAs such as eicosapentaenoic acid in transgenic plants. VLCPUFA biosynthesis requires repeated desaturation and repeated elongation of long chain fatty acid substrates. In previous experiments the production of eicosapentaenoic acid in transgenic plants was found to be limited by an unexpected bottleneck represented by the acyl exchange between the site of desaturation, endoplasmic reticulum-associated phospholipids, and the site of elongation, the cytosolic acyl-CoA pool. Here we report on the establishment of a coordinated, exclusively acyl-CoA-dependent pathway, which avoids the rate-limiting transesterification steps between the acyl lipids and the acyl-CoA pool during VLCPUFA biosynthesis. The pathway is defined by previously uncharacterized enzymes, encoded by cDNAs isolated from the microalga Mantoniella squamata. The conceptual enzymatic pathway was established and characterized first in yeast to provide proof-of-concept data for its feasibility and subsequently in seeds of Arabidopsis thaliana. The comparison of the acyl-CoA-dependent pathway with the known lipid-linked pathway for VLCPUFA biosynthesis showed that the acyl-CoA-dependent pathway circumvents the bottleneck of switching the Delta6-desaturated fatty acids between lipids and acyl-CoA in Arabidopsis seeds.

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.

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.

Jekyll encodes a novel protein involved in the sexual reproduction of barley

Cereal seed development depends on the intimate interaction of filial and maternal tissues, ensuring nourishment of the new generation. The gene jekyll, which was identified in barley (Hordeum vulgare), is preferentially expressed in the nurse tissues. JEKYLL shares partial similarity with the scorpion Cn4 toxin and is toxic when ectopically expressed in Escherichia coli and tobacco (Nicotiana tabacum). In barley, jekyll is upregulated in cells destined for autolysis. The gene generates a gradient of expression in the nucellar projection, which mediates the maternal-filial interaction during seed filling. Downregulation of jekyll by the RNA interference technique in barley decelerates autolysis and cell differentiation within the nurse tissues. Flower development and seed filling are thereby extended, and the nucellar projection no longer functions as the main transport route for assimilates. A slowing down in the proliferation of endosperm nuclei and a severely impaired ability to accumulate starch in the endosperm leads to the formation of irregular and small-sized seeds at maturity. Overall, JEKYLL plays a decisive role in the differentiation of the nucellar projection and drives the programmed cell death necessary for its proper function. We further suggest that cell autolysis during the differentiation of the nucellar projection allows the optimal provision of basic nutrients for biosynthesis in endosperm and embryo.

Ectopic expression of EFFECTOR OF TRANSCRIPTION perturbs gibberellin-mediated plant developmental processes

The plant hormone gibberellin (GA) is known to modulate various aspects of plant cell differentiation and development. The current model of GA-mediated regulation is based on a de-repressible system and includes specific protein modification and degradation. HRT, a zinc finger protein from barley has been shown to have GA-dependent transcriptional repressing activity on the seed-specific alpha-amylase promoter [Raventos, D., Skriver, K., Schlein, M., Karnahl, K., Rogers, S.W., Rogers, J.C. and Mundy, J. 1998. J. Biol. Chem. 273: 23313-23320]. Here we report the characterization of a dicot homologue from Brassica napus (BnET) and provide evidence for its role in GA response modulation suggesting that this could be a conserved feature of this gene family. When BnET is ectopically expressed in either Arabidopsis or tobacco the phenotypes include dwarfism due to shorter internodes and late flowering, reduced germination rate, increased anthocyanin content and reduced xylem lignification as a marker for terminal cell differentiation. Transient expression in protoplasts supports the notion that this most likely is due to a transcriptional repression of GA controlled genes. Finally, histological analysis showed that in contrast to other GA deficient mutants the shorter internodes were due to fewer but not smaller cells, suggesting a function of BnET in GA-mediated cell division control.

Developmental expression of ASG- 1 during gametogenesis in apomictic guinea grass (Panicum maximum)

We have used Western blue-visualized in situ-hybridization (ISH) to monitor the expression of apomixis-specific gene-1 (ASG-1, GenBank accession number AB000809) during gametogenesis in obligate-sexual and facultative-apomictic (aposporic) genotypes of guinea grass (Panicum maximum). The in situ-analysis revealed that ASG-1 is not expressed in the ovule during early floral development in both, the facultative apomicts (A1 stage) and the obligate sexuals (S1 stage). With the appearance of the aposporous initial cell(s) in the ovule of the apomictic type (A2-1 stage), ASG-1 expression is strong and specific to this apomixis-specific cell. ASG-1 expression continued through different stages of aposporous embryo sac development (A2-2 stage), indicating that the gene may play a role in this developmental process. Regular embryo sacs in sexual types did not show hybridization signals (S2 stage). However, strong ASG-1 expression was detected in immature pollen grains and young embryos in both reproductive types, suggesting that ASG-1 may be an allele derived from the obligate-sexual wild type. Expression in pollen grains faded with maturation. In a heterologous system, using Paspalum notatum, a facultative-aposporic tropical grass (bahia grass), identical results were obtained. The results are discussed in view of the fact, that ASG-1 shows some homology to genes known to be seed- or embryo-specific or involved in processes related to cell growth.

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.

The classical Ubisch bodies carry a sporophytically produced structural protein (RAFTIN) that is essential for pollen development

Pollen fecundity is crucial to crop productivity and also to biodiversity in general. Pollen development is supported by the tapetum, a metabolically active sporophytic nurse layer that devotes itself to this process. The tapetum in cereals and a vast majority of other plants is of the nonamoeboid type. Unable to reach out to microspores, it secretes nutrients into the anther locule where the microspores reside and develop. Orbicules (Ubisch bodies), studied in various plants since their discovery approximately 140 years ago, are a hallmark of the secretory tapetum. Their significance to tapetal or pollen development has not been established. We have identified in wheat and rice an anther-specific single-copy gene (per haploid genome equivalent) whose suppression in rice by RNA interference nearly eliminated the seed set. The flowers in the transgenics were normal for female functions, but the pollen collapsed and became less viable. Further characterization of the gene product, named RAFTIN, in wheat has shown that it is present in pro-orbicule bodies and it is accumulated in Ubisch bodies. Furthermore, it is targeted to microspore exine. Although the carboxyl portion of RAFTINs shares short, dispersed amino acid sequences (BURP domain) in common with a variety of proteins of disparate biological contexts, the occurrence RAFTIN per se is limited to cereals; neither the Arabidopsis genome nor the vast collection of ESTs suggests any obvious dicot homologs. Furthermore, our results show that RAFTIN is essential for the late phase of pollen development in cereals.

Module-specific regulation of the beta-phaseolin promoter during embryogenesis

The phas promoter displays stringent spatial regulation, being very highly expressed during embryogenesis and completely silent during all phases of vegetative development in bean, Phaseolus vulgaris. This pattern is maintained in transgenic tobacco and, as shown here, Arabidopsis. Dimethyl sulphate in vivo footprinting analyses revealed that over 20 cis-elements within the proximal 295 bp of the phas promoter are protected by factor binding in seed tissues whereas none are bound in leaves. The hypothesis that this complex profile represents a summation of several module (cotyledon, hypocotyl, and radicle)-specific factor-DNA interactions has been explored by the incorporation of site-directed substitution mutations into 10 locations within the -295phas promoter. Only 2.6% of -295phas promoter activity remained after mutation of the G-box; the CCAAAT box, the E-box and the RY elements were also found to mediate high levels of expression in embryos. Whereas the CACA element has dual positive and negative regulatory roles, the vicilin box was identified as a strong negative regulatory element. The proximal (-70 to -64) RY motif was found to bestow expression in the hypocotyl while all the RY elements contribute to expression in cotyledons but not to vascular tissue expression during embryogenesis. RY elements at positions -277 to -271, -260 to -254, and -237 to -231 were found to orchestrate radicle-specific repression. The G-box appears to be the functional abscisic acid responsive element and the E-site may be a coupling element. The results substantiate the concept that autarkical cis-element functions generate modular patterning during embryogenesis. They also reflect the existence of both redundancy and hierarchy in cis-element interactions. Importantly, the virtually identical expression patterns observed for the two distantly related plants studied argue strongly for the generality of function for the observed factor-element interactions.

Identification, structure, and differential expression of members of a BURP domain containing protein family in soybean

Expressed sequence tags (ESTs) exhibiting homology to a BURP domain containing gene family were identified from the Glycine max (L.) Merr. EST database. These ESTs were assembled into 16 contigs of variable sizes and lengths. Consistent with the structure of known BURP domain containing proteins, the translation products exhibit a modular structure consisting of a C-terminal BURP domain, an N-terminal signal sequence, and a variable internal region. The soybean family members exhibit 35-98% similarity in a -100-amino-acid C-terminal region, and a phylogenetic tree constructed using this region shows that some soybean family members group together in closely related pairs, triplets, and quartets, whereas others remain as singletons. The structure of these groups suggests that multiple gene duplication events occurred during the evolutionary history of this family. The depth and diversity of G. max EST libraries allowed tissue-specific expression patterns of the putative soybean BURPs to be examined. Consistent with known BURP proteins, the newly identified soybean BURPs have diverse expression patterns. Furthermore, putative paralogs can have both spatially and quantitatively distinct expression patterns. We discuss the functional and evolutionary implications of these findings, as well as the utility of EST-based analyses for identifying and characterizing gene families.

Amino acid permeases in developing seeds of Vicia faba L.: expression precedes storage protein synthesis and is regulated by amino acid supply

Full length cDNAs encoding three amino acid permeases were isolated from seed-specific libraries of Vicia faba. The predicted proteins VfAAP1, VfAAP3 and VfAAP4 share up to 66% identity among themselves. Functional characterization of VfAAP1 and VfAAP3 in a yeast mutant showed that these permeases transport a broad range of amino acids. However, VfAAP1 had a preference for cysteine and VfAAP3 for lysine and arginine. VfAAP1 was highly expressed in cotyledons at early developmental stages and moderately in other sink tissues. Its peak of expression in cotyledons corresponded to the appearance of storage protein transcripts, suggesting that this transporter fulfills an important role in providing amino acids for storage protein biosynthesis. VfAAP3 was expressed most abundantly in maternal tissues, that is in roots, stems, gynoecia, pods and seed coats at different developmental stages. VfAAP4 transcripts could not be detected by northern hybridization. In situ hybridization showed that VfAAP1 mRNA is distributed throughout cotyledon storage parenchyma cells, but could not be detected in the abaxial epidermal cell layer. It also accumulate in the chlorenchyma and thin-walled parenchyma cells of seed coats. VfAAP1 mRNA levels were lower in cotyledons cultured in the presence of glutamine, whereas expression of a vicilin storage protein gene was up-regulated under similar conditions. Cysteine repressed the expression of the GUS reporter gene under control of the VfAAP1 promoter, suggesting that this transporter is modulated at the transcriptional level. Regulation of amino acid transport in relation to storage protein accumulation is discussed.

Immunomodulation of phytohormones and functional proteins in plant cells

Recombinant antibodies expressed ectopically in plant cells recognize their corresponding antigens and can therefore bind specifically to phytohormones and proteins in vivo. The generation of antibody-antigen complexes interferes with the functions of the targets and affects the phenotype of transgenic plants. Recombinant antibodies can accumulate in different cell compartments and organs of transgenic plants at different stages of development. High levels of expression of specific, high-affinity antibodies are required for immunomodulation. Here, we discuss several models and examples of the antibody-mediated modulation of phytohormone and protein functions in terms of their potential for plant research.

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.

Isolation, characterization and cDNA cloning of nicotianamine synthase from barley. A key enzyme for iron homeostasis in plants

Basic cellular processes such as electron transport in photosynthesis and respiration require the precise control of iron homeostasis. To mobilize iron, plants have evolved at least two different strategies. The nonproteinogenous amino acid nicotianamine which is synthesized from three molecules of S-adenosyl-L-methionine, is an essential component of both pathways. This compound is missing in the tomato mutant chloronerva, which exhibits severe defects in the regulation of iron metabolism. We report the purification and partial characterization of the nicotianamine synthase from barley roots as well as the cloning of two corresponding gene sequences. The function of the gene sequence has been verified by overexpression in Escherichia coli. Further confirmation comes from reduction of the nicotianamine content and the exhibition of a chloronerva-like phenotype due to the expression of heterologous antisense constructs in transgenic tobacco plants. The native enzyme with an apparent Mr of approximately 105 000 probably represents a trimer of S-adenosyl-L-methionine-binding subunits. A comparison with the recently cloned chloronerva gene of tomato reveals striking sequence homology, providing support for the suggestion that the destruction of the nicotianamine synthase encoding gene is the molecular basis of the tomato mutation.

Molecular-cytogenetic characterization of the Vicia faba genome--heterochromatin differentiation, replication patterns and sequence localization

A comprehensive survey of the molecular-cytogenetic features of the Vicia faba chromosome complement (2n = 12) is given. It includes previous as well as new original data. Various Giemsa, restriction endonuclease and fluorochrome banding patterns, azacytidine-mediated segment extension, replication patterns, lateral A/T asymmetry and sequence localization data for tandemly arranged simple sequence repeats, dispersed repeats and coding sequences as well as histone acetylation patterns are considered. This allows not only to distinguish and characterize telomeres, subtelomeres, centromeres and the NOR, but also the structure of the 5S rRNA gene loci and two main types of interstitial heterochromatin. Additionally, it offers physical landmarks within euchromatic areas. Thus, the field bean genome, exemplified by the reconstructed karyotype ACB, belongs to the cytogenetically best investigated plant genomes.

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.

Identification of a cis-regulatory region of a gene in Arabidopsis thaliana whose induction by dehydration is mediated by abscisic acid and requires protein synthesis

In Arabidopsis thaliana, the induction of a dehydration-responsive gene, rd22, is mediated by abscisic acid (ABA) but the gene does not include any sequence corresponding to the consensus ABA-responsive element (ABRE), RYACGTGGYR, in its promoter region. The cis-regulatory region of the rd22 promoter was identified by monitoring the expression of beta-glucuronidase (GUS) activity in leaves of transgenic tobacco plants transformed with chimeric gene fusions constructed between 5'-deleted promoters of rd22 and the coding region of the GUS reporter gene. A 67-bp nucleotide fragment corresponding to positions -207 to -141 of the rd22 promoter conferred responsiveness to dehydration and ABA on a non-responsive promoter. The 67-bp fragment contains the sequences of the recognition sites for some transcription factors, such as MYC, MYB, and GT-1. The fact that accumulation of rd22 mRNA requires protein synthesis raises the possibility that the expression of rd22 might be regulated by one of these trans-acting protein factors whose de novo synthesis is induced by dehydration or ABA. Although the structure of the RD22 protein is very similar to that of a non-storage seed protein, USP, of Vicia faba, the expression of the GUS gene driven by the rd22 promoter in non-stressed transgenic Arabidopsis plants was found mainly in flowers and bolted stems rather than in seeds.

Localization of seed protein genes on metaphase chromosomes of Vicia faba via fluorescence in situ hybridization

Using fluorescence in situ hybridization (FISH), four different seed protein genes were physically mapped on metaphase chromosomes of Vicia faba L. dropped on slides. FISH with a 2.8 kb genomic probe of a legumin B4 gene resulted in reproducible signals on the long arm of chromosome III near the centromere. The same clone cross-hybridized at a lower frequency to the short arm of chromosome II, where the closely related legumin B3 gene family is located. The locus for legumin A-genes could be detected in the distal half of the long arm of chromosome V using a 1.7 kb cDNA clone. The locus of an unknown seed protein gene was mapped to the long arm of chromosome I using a mixture of polymerase chain reaction-amplified DNA fragments of the coding region of up to 1 kb in size.

Differentiation of field bean heterochromatin by in situ hybridization with a repeated FokI sequence

The chromosomes of a field bean line with a reconstructed karyotype (ACB) were hybridized in situ with biotinylated probes of a repetitive Fok I sequence, of DOP-PCR (degenerate oligonucleotide primed polymerase chain reaction) amplified DNA from a chromosome that does not contain this sequence, and with probes containing dispersed repetitive sequences. The results were compared with Giemsa banding, DNA late replication and Fok I in situ digestion patterns. This allowed further differentiation between the chromatin types of this species. Centromeric and NOR-associated heterochromatin as well as euchromatin were shown to be free of Fok I sequence repeats. Among the interstitial late replicating Giemsa bands, subdivided into 'marker' and 'additional' bands, most of the marker bands located at mid-arm positions were composed mainly or exclusively of tandemly arranged Fok I repeats. Some of the marker bands and nearly all of the additional bands located in the vicinity of centromeres were free of FokI sequence repeats, of Fok I recognition sites, and possibly also of dispersed repetitive sequences. They are probably composed of specific, not yet defined, repetitive sequences.

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.

Localization of seed protein genes on flow-sorted field bean chromosomes

Chromosomes from reconstructed field bean (Vicia faba L.) karyotypes were flow-sorted and the DNA was used for the physical localization of seed storage and nonstorage (USP) protein genes using PCR with sequence specific primers. The data were confirmed and refined by using DNA of microisolated chromosomes of other karyotypes as the target for PCR. The specificity of the PCR products was proved by restrictase digestion into fragments of predicted length or by reamplification using 'nested' primers. The genes are located within defined regions of chromosome I (USP = unknown seed protein genes), II (vicilin genes, legumin B3 genes), III (legumin B4 genes), IV (pseudogenes psi 1) and V (legumin A genes and pseudogenes psi 1). Except for the pseudogene derived from the sequence of legumin B4 gene, all members of each gene family are located in one chromosome region exclusively. This approach proved to be useful for localizing genes that cannot be mapped genetically (due to the lack of allelic variants) and might be applied to integrate physical and genetic maps.

The plant hormone abscisic acid mediates the drought-induced expression but not the seed-specific expression of rd22, a gene responsive to dehydration stress in Arabidopsis thaliana

Nine cDNA clones, corresponding to genes that are responsive to dehydration (named RD), have been isolated from Arabidopsis thaliana. The sequence of a putative protein encoded by one of the RD cDNA clones, RD22, exhibits considerable homology to an unidentified seed protein (USP) of Vicia faba. Northern analysis showed that RD22 mRNA is induced by salt stress as well as by water deficit but not by cold or heat stress. RD22 mRNA appeared after the application of abscisic acid (ABA), an indication that transcription of RD22 mRNA is induced by endogenous ABA, the production of which is triggered by drought and salt stress. The induction of RD22 mRNA by ABA was inhibited by cycloheximide. Thus, it appears that protein synthesis is required for the induction of this mRNA by ABA. By contrast, protein synthesis was not required for the ABA-responsive induction RD29 mRNA, which corresponds to another dehydration-responsive gene of A. thaliana. These results suggest that there are at least two mechanisms for the induction of dehydration-responsive genes by ABA. RD22 mRNA was also expressed during the early and middle stages of seed development, showing a pattern of expression similar to that of USP. The seed-specific expression of RD22 seems not to be regulated by ABA. Structural analysis of the RD22 genomic clone revealed that the structural gene (designated rd22) contains three introns, and only a single copy of the gene is present in the A. thaliana genome, while the gene for USP from V. faba is actually a family of genes with 10 to 20 members.(ABSTRACT TRUNCATED AT 250 WORDS)

Organ-dependent regulation of a plant promoter isolated from rice by 'promoter-trapping' in tobacco

A vector containing a transcriptionally inactive neomycin phosphotransferase II gene was used to select promoter sequences from a pool of random genomic DNA fragments. This paper describes how one such sequence (P4.7) isolated from Oryza sativa acts as a hormonally regulated promoter in Nicotiana tabacum. Relative expression ratios in leaf, root, midrib, callus, and stem tissue of tobacco plants are 1:5:4:10:17. Histochemical assays show that P4.7 activates the uidA reporter gene throughout the phloem and cortex of tobacco stems. Transcription from the P4.7 fragment is inducible in leaf tissue by low levels of alpha-naphthalene acetic acid or 6-benzyl-aminopurine, even when cell proliferation is inhibited by colchicine or hydroxyurea. Conversely, 1% DMSO was found to inhibit activation of P4.7 without interfering with callus formation. The fragment contains TATA and CAAT sequences normally found at the 5' end of many plant genes, and an additional region homologous to sequences located in similar positions in a variety of similarly regulated promoters. Promoter deletion and fusion experiments have indicated the location of a stem enhancer element in P4.7. The promoter trap system we have described may potentially be used to characterize transcriptional factors common to monocot and dicot species.

A novel seed protein gene from Vicia faba is developmentally regulated in transgenic tobacco and Arabidopsis plants

We have isolated a novel gene, denoted USP, from Vicia faba var. minor, which corresponds to the most abundant mRNA present in cotyledons during early seed development; however, the corresponding protein does not accumulate in cotyledons. The characterized USP gene with its two introns is 1 of about 15 members of a gene family. A fragment comprising 637 bp of 5' flanking sequence and the total 5' untranslated region was shown to be sufficient to drive the mainly seed-specific expression of two reporter genes, coding for neomycin phosphotransferase II and beta-glucuronidase, in transgenic Arabidopsis thaliana and Nicotiana tabacum plants. We showed that the USP promoter becomes active in transgenic tobacco seeds in both the embryo and the endosperm, whereas its activity in Arabidopsis is detectable only in the embryo. Moreover, we demonstrated a transient activity pattern of the USP promoter in root tips of both transgenic host species.

Upstream sequences regulating legumin gene expression in heterologous transgenic plants

We have previously isolated a legumin gene LeB4 from Vicia faba and shown that a 4.7 kb DNA fragment containing the gene leads to seed-specific expression in transgenic tobacco plants. Here we report that the 2.4 kb upstream sequence alone, when fused to either the neomycin phosphotransferase II (nptII) gene or the beta-glucuronidase (uidA) gene, leads to high enzyme levels in transgenic seeds of both tobacco and Arabidopsis. beta-Glucuronidase (GUS) activity is especially intense in the cotyledons fading out towards the embryonal root tip, a result confirmed by in situ hybridization. Staining of endosperm cells is consistent in both species. Analysis of a series of promoter deletion mutants fused to the nptII gene and introduced into tobacco plants revealed that about 1 kb of 5'-flanking sequence is sufficient for high-level expression but indirect evidence suggests the presence of weak positive regulatory elements further upstream. Deletions leaving only 0.2 kb of upstream sequence reduce enzyme levels to less than 10%. A deletion which destroys the legumin box with its seed protein gene-specific CATGCATG motif has no obvious effects on expression levels.