Activity of a maize ubiquitin promoter in transgenic rice

Characterization of Cop I coat proteins in plant cells

Membrane traffic in eukaryotic cells is mediated by COP (coat protein)-coated vesicles. Their existence in plant cells has not yet been unequivocally demonstrated, although coated vesicles (probably with a COP coat) can be seen by electron microscopy. At the gene level, plant cells seem to contain all the components necessary to form COP-coated vesicles. In this paper, we have used antibodies raised against mammalian COPI coat proteins to detect putative homologues in rice (Oryza sativa) cells. Using these antibodies, we have found that rice cells contain alpha-, beta-, beta'-, and gamma-COP, as well as ADP-ribosylation factor (ARF) 1 protein. In addition, we show that antibodies against mammalian beta'-COP can immunoprecipitate not only beta'-COP but also alpha-, beta-, and gamma-COP, suggesting that COPI components in rice cells exist as a complex (or coatomer) in the cytosol, as in mammalian cells. Finally, we show that COP binding to membranes is GTP-dependent, and that ARF1 also binds to membranes in a GTP-dependent manner.

The maize streak virus coat protein transcription unit exhibits tissue-specific expression in transgenic rice

Maize streak geminivirus (MSV) is a single-stranded DNA virus that infects cereals and other grasses. A promoter region incorporating the MSV large intergenic region and movement protein gene sequence was ligated to the gus (beta-glucuronidase) reporter gene which replaced the virus coat protein (CP) gene. The CP promoter activity was analysed in transgenic rice plants (Oryza sativa L.) and was compared with that obtained in plants transformed with the gus gene downstream of the cauliflower mosaic virus (CaMV) 35S promoter. The MSV CP promoter activity varied in the five plant lines tested, but was always less than that of the CaMV promoter. Histochemistry showed that the MSV CP promoter was active in cells of regenerating callus but in regenerated plants it provided an expression pattern restricted to the vascular tissues of the root, stem, leaf and floral organs. Expression was highest in phloem-associated tissues of the vegetative organs and was absent from the tip and elongation region of seedling roots. Thus, the MSV CP promoter shows a degree of developmental regulation and can be used to confer tissue-specific expression in transgenic rice plants.

Molecular farming of industrial proteins from transgenic maize

Recombinant egg white avidin and bacterial B-glucuronidase (GUS) from transgenic maize have been commercially produced. High levels of expression were obtained in seed by employing the ubiquitin promoter from maize. The recombinant proteins had activities that were indistinguishable from their native counterparts. We have illustrated that down-stream activities in the production of these recombinant proteins, such as stabilizing the germplasm and processing for purification, were accomplished without any major obstacles. Avidin (A8706) and GUS (G2035) are currently marketed by Sigma Chemical Co.

Characterization and expression of a heptaubiquitin gene from tomato

Ubiquitin is highly conserved 76 amino acid protein involved, among other functions, in the selective degradation of proteins in the cell. From a tomato (Lycopersicon esculentum Mill. cv. Craigella) genomic library, we have isolated a clone encoding a polyubiquitin gene, designated ubq1-1 comprising seven repeats of ubiquitin and two C-terminal extension amino acids. The ubq1-1 gene contains an intron of 1128bp immediately upstream of the translation start codon. DNA sequence comparison revealed that the 5' and 3' non-coding regions of the tomato ubq1-1 gene are nearly identical to the sequence of a polyubiquitin cDNA clone isolated from potato (Garbarino et al., 1992; Plant Mol. Biol. 20, 235-244). The ubq1-1 gene is expressed in leaves to rather low levels in tomato, and the abundance of ubq1-1 transcripts is increased under heat shock conditions. For functional analyses, a chimeric gene construct containing the intron and 1.6kb of ubq1-1 sequence 5' to the intron fused to the gus reporter gene was introduced into the tobacco genome. In leaves of transgenic tobacco plants, reporter gene expression was generally lower from the ubq1-1 promoter than from the cauliflower mosaic virus 35S RNA promoter. In addition, the tomato ubq1-1 promoter was not found to respond to heat shock in transgenic tobacco plants. Histochemical analysis of the plants demonstrated localization of gus reporter gene activity in the vascular systems of the leaves and the roots. Deletion of the intron from the reporter gene construct markedly reduced reporter gene expression in transformed tobacco plants, thus suggesting that the intron may influence transcript levels deriving from the ubq1-1 promoter.

Agrobacterium-transformed rice plants expressing synthetic cryIA(b) and cryIA(c) genes are highly toxic to striped stem borer and yellow stem borer

Over 2,600 transgenic rice plants in nine strains were regenerated from >500 independently selected hygromycin-resistant calli after Agrobacterium-mediated transformation. The plants were transformed with fully modified (plant codon optimized) versions of two synthetic cryIA(b) and cryIA(c) coding sequences from Bacillus thuringiensis as well as the hph and gus genes, coding for hygromycin phosphotransferase and beta-glucuronidase, respectively. These sequences were placed under control of the maize ubiquitin promoter, the CaMV35S promoter, and the Brassica Bp10 gene promoter to achieve high and tissue-specific expression of the lepidopteran-specific delta-endotoxins. The integration, expression, and inheritance of these genes were demonstrated in R0 and R1 generations by Southern, Northern, and Western analyses and by other techniques. Accumulation of high levels (up to 3% of soluble proteins) of CryIA(b) and CryIA(c) proteins was detected in R0 plants. Bioassays with R1 transgenic plants indicated that the transgenic plants were highly toxic to two major rice insect pests, striped stem borer (Chilo suppressalis) and yellow stem borer (Scirpophaga incertulas), with mortalities of 97-100% within 5 days after infestation, thus offering a potential for effective insect resistance in transgenic rice plants.

Ectopic expression of the maize kn1 gene phenocopies the Hooded mutant of barley

The homeobox gene, knotted1, (kn1) is expressed in shoot meristems and is required for maintaining indeterminacy and preventing cellular differentiation. Awns, extensions of the bract-like lemma found in all grass inflorescences, are normally determinate structures. We show that ectopic expression of kn1 in the barley awn is sufficient to direct the development of ectopic meristems, forming inflorescence-like structures. This homeotic transformation is similar to the phenotype produced by misexpression of the barley hvknox3 gene, associated with the dominant Hooded mutant (Muller, K. J., Romano, N., Gerstner, O., Garcia-Maroto, F., Pozzi, C., Salamini, F. and Rohde, W. (1995) Nature 374, 727–730). We suggest that the inverse polarity of the ectopic flowers seen in Hooded and transgenic kn1 plants results from the transformation of the awn into reiterative inflorescence axes. We observed that the protein and mRNA localization of the transgene, driven by a constitutive promoter, is similar to the expression pattern of hvknox3 in awns of Hooded mutants, suggesting posttranscriptional regulation.

Evaluation of five promoters for use in transformation of oil palm (Elaeis guineensis Jacq.)

The efficiency of GUS (β-Glucuronidase) gene expression in embryogenic callus and young leaflets of mature and seedling palm after microprojectile bombardment with five constructs (pEmuGN, pAHC25, pAct1-F4, pGH24 and pBARGUS) was evaluated to identify the most suitable promoter(s) to use in transformation attempts in oil palm. Expression of the GUS gene driven by theEmu, Ubi1, Act1 35S orAdh1 was assayed, both histochemically and fluorometrically, from a total of 200 plates of tissues in eight independent experiments two days after bombardment. A completely randomized experimental design was used for each experiment, and the data analysed by ANOVA and Duncan's Multiple Range Test. The expression level of GUS driven by theEmu orUbi1 promoters was significantly higher than that of the Act], 35S and Adhl promoters in many experiments, and that of theAdhl was significantly lower than those of the other four promoters. Both histochemical and fluorometric data indicate that in embryogenic callus, the expression of theEmu promoter was higher than that of theUbi1 whereas in young leaflets from mature palm the Ubi1 expression was stronger. The performances of the five promoters were also tested in tobacco callus using a fluorometric GUS assay. The activity of the 35S promoter was highest, and significantly different from that of all the other promoters except theEmu, and that of theAct1 promoter was lowest. These results indicate that either theUbil orEmu promoter should facilitate the expression of desired genes in oil palm and aid in development of an efficient stable transformation system.

T-DNA integration into genomic DNA of rice following Agrobacterium inoculation of isolated shoot apices

This paper establishes that the isolated shoot meristem of monocotyledons can be infected and transformed using Agrobacterium. Since this explant from nearly any cereal cultivar can rapidly regenerate into a plant, using this explant effectively eliminates the genotype regeneration restrictions to cereal crop transformation allowing direct transformation of elite germplasm. Shoot apices of Oryza sativa L. Tropical Japonica, cv. Maybelle were explants used for cocultivation, and gene transfer was accomplished using Agrobacterium containing plasmids for the bar gene expression driven by the CaMV 35S promoter or by the rice actin 1 promoter. Experiments to determine the survival rates of isolated shoot apices on media containing the herbicide, glufosinate-ammonium (PPT), established that no shoot apices survived on 0.5 or 1.0 mg/l PPT. After shoot apices were cocultivated with Agrobacterium, 2.8% (overall 20 out of 721 shoot apices) survived on 0.5 mg/l PPT. Results demonstrated that the use of the actin 1 promoter-based expression vector and an extra-wounding treatment of the meristematic cells appeared to be most effective in promoting transformation. Integration, expression and transmission of the transferred foreign genes in primary, R1 and R2 generation plants were confirmed by molecular analyses and herbicide application tests. A germination test of R2 progeny from one of the transgenic plants (R1) established a phenotype segregation ratio showing a non-Mendelian inheritance pattern. Inactivation of the transferred foreign gene in R2 progeny appeared to result from transgene methylation.

Expression of a novel high-molecular-weight glutenin subunit gene in transgenic wheat

High-molecular-weight glutenin subunits (HMW-GS), one class of seed storage proteins, are important determinants of the bread-making quality of wheat flour. To change the amount and composition of these proteins via genetic engineering, a gene encoding a novel hybrid subunit under the control of native HMW-GS regulatory sequences was inserted into wheat. Of 26 independent transgenic lines identified by bialaphos selection, 18 expressed the cotransformed hybrid HMW-GS gene in their seed. The hybrid subunit accumulated to levels comparable to those of the native HMW-GS. These results show that a native HMW-GS gene promoter can be used to obtain high levels of expression of seed storage and, potentially, other proteins in transgenic wheat endosperm. Transgene expression was stable for at least three seed generations in the majority of lines. These experiments demonstrate the feasibility of constructing wheat plants with novel seed protein compositions.

Ubiquitin promoter-based vectors for high-level expression of selectable and/or screenable marker genes in monocotyledonous plants

A set of plasmids has been constructed utilizing the promoter, 5' untranslated exon, and first intron of the maize ubiquitin (Ubi-1) gene to drive expression of protein coding sequences of choice. Plasmids containing chimaeric genes for ubiquitin-luciferase (Ubi-Luc), ubiquitin-beta-glucuronidase (Ubi-GUS), and ubiquitin-phosphinothricin acetyl transferase (Ubi-bar) have been generated, as well as a construct containing chimaeric genes for both Ubi-GUS and Ubi-bar in a single plasmid. Another construct was generated to allow cloning of protein coding sequences of choice on Bam HI and Bam HI-compatible restriction fragments downstream of the Ubi-1 gene fragment. Because the Ubi-1 promoter has been shown to be highly active in monocots, these constructs may be useful for generating high-level gene expression of selectable markers to facilitate efficient transformation of monocots, to drive expression of reference reporter genes in studies of gene expression, and to provide expression of biotechnologically important protein products in transgenic plants.

Activity of constitutive promoters in various species from the Liliaceae

In this paper we first review literature on the performance of various promoters in monocotyledonous species. In general, promoters isolated from monocots show a higher activity in monocot species. Moreover, the presence of an intron between the promoter and reporter gene increases transcription levels. We used the same approach to study gene expression in Liliaceae. The activities of the CaMV 35S, maize Adh1-based pEmu, rice Act1 and maize Ubi promoters, coupled to the beta-glucuronidase (gus) reporter gene, were evaluated for transient gene expression upon particle bombardment of tissues of tobacco, rice, tulip, lily and leek. Although monocot promoters performed very well in rice tissues, the results of this study show that this cannot be generalized for other monocot species. The transcription inducing effects of monocot promoters were less pronounced or even absent in tissues of Liliaceae, while the presence of an intron between promoter and gus gene reduced promoter activity.

Non-systemic expression of a stress-responsive maize polyubiquitin gene (Ubi-1) in transgenic rice plants

We have used the promoter, 1st exon and 1st intron of the maize polyubiquitin gene (Ubi-1) for rice transformation experiments and revealed the characteristic expression of Ubi-1 gene: (1) Ubi-1 gene is not regulated systemically but rather individual cells respond independently to the heat or physical stress; (2) Ubi-1 gene changes its tissue-specific expression in response to stress treatment; (3) the expression of Ubi-1 gene is dependent on cell cycle.