pEmu: an improved promoter for gene expression in cereal cells

Genetic manipulation of trehalose-6-phosphate synthase results in changes in the soluble sugar profile in transgenic sugarcane stems

Trehalose is a non-reducing disaccharide widely distributed in nature. The trehalose biosynthetic intermediate, trehalose 6-phosphate (Tre6P) is an essential regulatory and signaling molecule involved in both regulation of carbon metabolism and photosynthesis. To investigate the effect of altered trehalose synthesis on sucrose accumulation in sugarcane (Saccharum spp. hybrid), we independently overexpressed the Escherichia coli otsA (trehalose-6-phosphate synthase; TPS) and otsB (trehalose-6-phosphate phosphatase; TPP) genes and additionally partially silenced native TPS expression. In mature cane, sucrose levels in the otsA transgenic plants were lowered, whereas sucrose levels in the otsB transgenic plants were increased. Partial silencing of TPS expression in sugarcane transformed with a TPS-targeted microRNA recombinant construct was confirmed in leaf and mature internode tissue of transgenic plants. Most of the silencing transgenic lines accumulated trehalose at lower levels than the wild-type (WT) plants. The immature stalk tissue of these transgenic lines had lower levels of glucose and fructose, whereas the mature internode tissue had lower sucrose and glucose levels, when compared with the WT. Furthermore, various minor metabolites and sugars were detected in the sugarcane plants, which mostly decreased as the stalk tissue of the cane matured. The results demonstrate that manipulation of Tre6P/trehalose metabolism has the potential to modify the profile of soluble sugars accumulated in sugarcane stems.

WY195, a New Inducible Promoter From the Rubber Powdery Mildew Pathogen, Can Be Used as an Excellent Tool for Genetic Engineering

Until now, there are few studies and reports on the use of endogenous promoters of obligate biotrophic fungi. The WY195 promoter in the genome of Oidium heveae, the rubber powdery mildew pathogen, was predicted using PromoterScan and its promoter function was verified by the transient expression of the β-glucuronidase (GUS) gene. WY195 drove high levels of GUS expression in dicotyledons and monocotyledons. qRT-PCR indicated that GUS expression regulated by the WY195 promoter was 17.54-fold greater than that obtained using the CaMV 35S promoter in dicotyledons (Nicotiana tabacum), and 5.09-fold greater than that obtained using the ACT1 promoter in monocotyledons (Oryza sativa). Furthermore, WY195-regulated GUS gene expression was induced under high-temperature and drought conditions. Soluble proteins extracted from WY195-hpaXm transgenic tobacco was bioactive. Defensive micro-HR induced by the transgene expression of hpaXm was observed on transgenic tobacco leaves. Disease resistance bioassays showed that WY195-hpaXm transgenic tobacco enhanced the resistance to tobacco mosaic virus (TMV). WY195 has great potential for development as a new tool for genetic engineering. Further in-depth studies will help to better understand the transcriptional regulation mechanisms and the pathogenic mechanisms of O. heveae.

Identification of sugar response complex in the metallothionein OsMT2b gene promoter for enhancement of foreign protein production in transgenic rice

A 146-bp sugar response complex MTSRC is identified in the promoter of rice metallothionein OsMT2b gene conferring high-level expression of luciferase reporter gene and bioactive recombinant haFGF in transgenic rice. A rice subfamily type 2 plant metallothionein (pMT) gene, OsMT2b, encoding a reactive oxygen species (ROS) scavenger protein, has been previously shown to exhibit the most abundant gene expression in young rice seedling. Expression of OsMT2b was found to be regulated negatively by ethylene and hydrogen peroxide in rice stem node under flooding stress, but little is known about its response to sugar depletion. In this study, transient expression assay and transgenic approach were employed to characterize the regulation of the OsMT2b gene expression in rice. We found that the expression of OsMT2b gene is induced by sugar starvation in both rice suspension cells and germinated embryos. Deletion analysis and functional assay of the OsMT2b promoter revealed that the 5'-flanking region of the OsMT2b between nucleotides - 351 and - 121, which contains the sugar response complex (- 266 to - 121, designated MTSRC) is responsible for high-level promoter activity under sugar starvation. It was also found that MTSRC significantly enhances the Act1 promoter activity in transgenic rice cells and seedlings. The modified Act1 promoter, Act1-MTSRC, was used to produce the recombinant human acidic fibroblast growth factor (haFGF) in rice cells. Our result shows that the bioactive recombinant haFGF is stably produced in transformed rice cell culture and yields are up to 2% of total medium proteins. Our studies reveal that MTSRC serves as a strong transcriptional activator and the Act1-MTSRC promoter can be applicable in establishing an efficient expression system for the high-level production of foreign proteins in transgenic rice cells and seedlings.

A Brief History of Promoter Development for Use in Transgenic Maize Applications

Promoters regulate gene expression, and are essential biotechnology tools. Since its introduction in the mid-1990s, biotechnology has greatly enhanced maize productivity primarily through the development of insect control and herbicide tolerance traits. Additional biotechnology applications include improving seed nutrient composition, industrial protein production, therapeutic production, disease resistance, abiotic stress resistance, and yield enhancement. Biotechnology has also greatly expanded basic research into important mechanisms that govern plant growth and reproduction. Many novel promoters have been developed to facilitate this work, but only a few are widely used. Transgene optimization includes a variety of strategies some of which effect promoter structure. Recent reviews examine the state of the art with respect to transgene design for biotechnology applications. This chapter examines the use of transgene technology in maize, focusing on the way promoters are selected and used. The impact of new developments in genomic technology on promoter structure is also discussed.

Sugarcane Water Stress Tolerance Mechanisms and Its Implications on Developing Biotechnology Solutions

Sugarcane is a unique crop with the ability to accumulate high levels of sugar and is a commercially viable source of biomass for bioelectricity and second-generation bioethanol. Water deficit is the single largest abiotic stress affecting sugarcane productivity and the development of water use efficient and drought tolerant cultivars is an imperative for all major sugarcane producing countries. This review summarizes the physiological and molecular studies on water deficit stress in sugarcane, with the aim to help formulate more effective research strategies for advancing our knowledge on genes and mechanisms underpinning plant response to water stress. We also overview transgenic studies in sugarcane, with an emphasis on the potential strategies to develop superior sugarcane varieties that improve crop productivity in drought-prone environments.

Sugarcane Water Stress Tolerance Mechanisms and Its Implications on Developing Biotechnology Solutions

Sugarcane is a unique crop with the ability to accumulate high levels of sugar and is a commercially viable source of biomass for bioelectricity and second-generation bioethanol. Water deficit is the single largest abiotic stress affecting sugarcane productivity and the development of water use efficient and drought tolerant cultivars is an imperative for all major sugarcane producing countries. This review summarizes the physiological and molecular studies on water deficit stress in sugarcane, with the aim to help formulate more effective research strategies for advancing our knowledge on genes and mechanisms underpinning plant response to water stress. We also overview transgenic studies in sugarcane, with an emphasis on the potential strategies to develop superior sugarcane varieties that improve crop productivity in drought-prone environments.

Synthetic promoters in planta

This paper reviews the importance, prospective and development of synthetic promoters reported in planta. A review of the synthetic promoters developed in planta would help researchers utilize the available resources and design new promoters to benefit fundamental research and agricultural applications. The demand for promoters for the improvement and application of transgenic techniques in research and agricultural production is increasing. Native/naturally occurring promoters have some limitations in terms of their induction conditions, transcription efficiency and size. The strength and specificity of native promoter can be tailored by manipulating its 'cis-architecture' by the use of several recombinant DNA technologies. Newly derived chimeric promoters with specific attributes are emerging as an efficient tool for plant molecular biology. In the last three decades, synthetic promoters have been used to regulate plant gene expression. To better understand synthetic promoters, in this article, we reviewed promoter structure, the scope of cis-engineering, strategies for their development, their importance in plant biology and the total number of such promoters (188) developed in planta to date; we then categorized them under different functional regimes as biotic stress-inducible, abiotic stress-inducible, light-responsive, chemical-inducible, hormone-inducible, constitutive and tissue-specific. Furthermore, we identified a set of 36 synthetic promoters that control multiple types of expression in planta. Additionally, we illustrated the differences between native and synthetic promoters and among different synthetic promoter in each group, especially in terms of efficiency and induction conditions. As a prospective of this review, the use of ideal synthetic promoters is one of the prime requirements for generating transgenic plants suitable for promoting sustainable agriculture and plant molecular farming.

Comparison of the MpEF1α and CaMV35 promoters for application in Marchantia polymorpha overexpression studies

Constitutive promoters are essential tools for analyses of gene functions by transgenic approaches. For overexpression and silencing studies of genes, a ubiquitous and strong expression of genes under investigation as well as selection markers is preferred. For future applications in the emerging basal plant model system Marchantia polymorpha, a liverwort, activities of the viral 35S cauliflower mosaic virus promoter and the endogenous elongation factor 1α (MpEF1α) promoter were analyzed. Expression of the reporter gene β-glucuronidase (GUS), driven by the CaMV35 and MpEF1α promoters, was compared throughout plant development. Significant differences were observed between the two promoter activities. The CaMV35 promoter yields a weak reporter gene expression in the meristematic zones but drives a strong expression in the thallus. The MpEF1α promoter causes a strong meristematic GUS expression and is more active in female sexual tissues. Overall, the MpEF1α promoter seems to be the better option for obtaining a strong and ubiquitous transgene expression. Furthermore, a whole mount in situ hybridization protocol for Marchantia was established. Analysis of MpEF1α mRNA transcript in intact, whole tissues showed an expression pattern that is overall similar to the pattern of the GUS reporter gene expression driven by the MpEF1α promoter, including strong expression in meristematic zones. The whole mount technique reported here can be used to determine the mRNA expression in intact gemmae and archegonia, and has the potential to be applied for screening large numbers of transgenic plants, for instance to identify knock-down mutants.

Enhanced transgene expression in rice following selection controlled by weak promoters

BACKGROUND

Techniques that enable high levels of transgene expression in plants are attractive for the commercial production of plant-made recombinant pharmaceutical proteins or other gene transfer related strategies. The conventional way to increase the yield of desired transgenic products is to use strong promoters to control the expression of the transgene. Although many such promoters have been identified and characterized, the increase obtainable from a single promoter is ultimately limited to a certain extent.

RESULTS

In this study, we report a method to magnify the effect of a single promoter by using a weak promoter-based selection system in transgenic rice. tCUP1, a fragment derived from the tobacco cryptic promoter (tCUP), was tested for its activity in rice by fusion to both a β-glucuronidase (GUS) reporter and a hygromycin phosphotransferase (HPT) selectable marker. The tCUP1 promoter allowed the recovery of transformed rice plants and conferred tissue specific expression of the GUS reporter, but was much weaker than the CaMV 35S promoter in driving a selectable marker for growth of resistant calli. However, in the resistant calli and regenerated transgenic plants selected by the use of tCUP1, the constitutive expression of green fluorescent protein (GFP) was dramatically increased as a result of the additive effect of multiple T-DNA insertions. The correlation between attenuated selection by a weak promoter and elevation of copy number and foreign gene expression was confirmed by using another relatively weak promoter from nopaline synthase (Nos).

CONCLUSIONS

The use of weak promoter derived selectable markers leads to a high T-DNA copy number and then greatly increases the expression of the foreign gene. The method described here provides an effective approach to robustly enhance the expression of heterogenous transgenes through copy number manipulation in rice.

Development of useful recombinant promoter and its expression analysis in different plant cells using confocal laser scanning microscopy

BACKGROUND

Designing functionally efficient recombinant promoters having reduced sequence homology and enhanced promoter activity will be an important step toward successful stacking or pyramiding of genes in a plant cell for developing transgenic plants expressing desired traits(s). Also basic knowledge regarding plant cell specific expression of a transgene under control of a promoter is crucial to assess the promoter's efficacy.

METHODOLOGY/PRINCIPAL FINDINGS

We have constructed a set of 10 recombinant promoters incorporating different up-stream activation sequences (UAS) of Mirabilis mosaic virus sub-genomic transcript (MS8, -306 to +27) and TATA containing core domains of Figwort mosaic virus sub-genomic transcript promoter (FS3, -271 to +31). Efficacies of recombinant promoters coupled to GUS and GFP reporter genes were tested in tobacco protoplasts. Among these, a 369-bp long hybrid sub-genomic transcript promoter (MSgt-FSgt) showed the highest activity in both transient and transgenic systems. In a transient system, MSgt-FSgt was 10.31, 2.86 and 2.18 times more active compared to the CaMV35S, MS8 and FS3 promoters, respectively. In transgenic tobacco (Nicotiana tabaccum, var. Samsun NN) and Arabidopsis plants, the MSgt-FSgt hybrid promoter showed 14.22 and 7.16 times stronger activity compared to CaMV35S promoter respectively. The correlation between GUS activity and uidA-mRNA levels in transgenic tobacco plants were identified by qRT-PCR. Both CaMV35S and MSgt-FSgt promoters caused gene silencing but the degree of silencing are less in the case of the MSgt-FSgt promoter compared to CaMV35S. Quantification of GUS activity in individual plant cells driven by the MSgt-FSgt and the CaMV35S promoter were estimated using confocal laser scanning microscopy and compared.

CONCLUSION AND SIGNIFICANCE

We propose strong recombinant promoter MSgt-FSgt, developed in this study, could be very useful for high-level constitutive expression of transgenes in a wide variety of plant cells.

Isolation and characterization of an oil palm constitutive promoter derived from a translationally control tumor protein (TCTP) gene

We have characterized an oil palm (Elaeis guineensis Jacq.) constitutive promoter that is derived from a translationally control tumor protein (TCTP) gene. The TCTP promoter was fused transcriptionally with the gusA reporter gene and transferred to monocot and dicot systems in order to study its regulatory role in a transient expression study. It was found that the 5' region of TCTP was capable of driving the gusA expression in all the oil palm tissues tested, including immature embryo, embryogenic callus, embryoid, young leaflet from mature palm, green leaf, mesocarp and stem. It could also be used in dicot systems as it was also capable of driving gusA expression in tobacco leaves. The results indicate that the TCTP promoter could be used for the production of recombinant proteins that require constitutive expression in the plant system.

Designer promoter: an artwork of cis engineering

Advances in systematic computational biology and rapid elucidation of synergistic interplay between cis and trans factors governing transcriptional control have facilitated functional annotation of gene networks. The generation of data through deconstructive, reconstructive and database assisted promoter studies, and its integration to principles of synthetic engineering has started an era of designer promoters. Exploration of natural promoter architecture and the concept of cis engineering have not only enabled fine tuning of single or multiple transgene expression in response to perturbations in the chemical, physiological and environmental stimuli but also provided researchers with a unique answer to various problems in crop improvement in the form of bidirectional promoters.

Testing the IMEter on rice introns and other aspects of intron-mediated enhancement of gene expression

In many eukaryotes, spliceosomal introns are able to influence the level and site of gene expression. The mechanism of this Intron Mediated Enhancement (IME) has not yet been elucidated, but regulation of gene expression is likely to occur at several steps during and after transcription. Different introns have different intrinsic enhancing properties, but the determinants of these differences remain unknown. Recently, an algorithm called IMEter, which is able to predict the IME potential of introns without direct testing, has been proposed. A computer program was developed for Arabidopsis thaliana and rice (Oryza sativa L.), but was only tested experimentally in Arabidopsis by measuring the enhancement effect on GUS expression of different introns inserted within otherwise identical plasmids. To test the IMEter potential in rice, a vector bearing the upstream regulatory sequence of a rice β-tubulin gene (OsTub6) fused to the GUS reporter gene was used. The enhancing intron interrupting the OsTub6 5'-UTR was precisely replaced by seven other introns carrying different features. GUS expression level in transiently transformed rice calli does not significantly correlate with the calculated IMEter score. It was also found that enhanced GUS expression was mainly due to a strong increase in the mRNA steady-state level and that mutations at the splice recognition sites almost completely abolished the enhancing effect. Splicing also appeared to be required for IME in Arabidopsis cell cultures, where failure of the OsTub6 5' region to drive high level gene expression could be rescued by replacing the poorly spliced rice intron with one from Arabidopsis.

Transgene expression systems in the Triticeae cereals

The control of transgene expression is vital both for the elucidation of gene function and for the engineering of transgenic crops. Given the dominance of the Triticeae cereals in the agricultural economy of the temperate world, the development of well-performing transgene expression systems of known functionality is of primary importance. Transgenes can be expressed either transiently or stably. Transient expression systems based on direct or virus-mediated gene transfer are particularly useful in situations where the need is to rapidly screen large numbers of genes. However, an unequivocal understanding of gene function generally requires that a transgene functions throughout the plant's life and is transmitted through the sexual cycle, since this alone allows its effect to be decoupled from the plant's response to the generally stressful gene transfer event. Temporal, spatial and quantitative control of a transgene's expression depends on its regulatory environment, which includes both its promoter and certain associated untranslated region sequences. While many transgenic approaches aim to manipulate plant phenotype via ectopic gene expression, a transgene sequence can be also configured to down-regulate the expression of its endogenous counterpart, a strategy which exploits the natural gene silencing machinery of plants. In this review, current technical opportunities for controlling transgene expression in the Triticeae species are described. Apart from protocols for transient and stable gene transfer, the choice of promoters and other untranslated regulatory elements, we also consider signal peptides, as they too govern the abundance and particularly the sub-cellular localization of transgene products.

Effect of promoter driving selectable marker on corn transformation

Identification of an appropriate selection agent and its corresponding selectable marker gene is one of the first steps in establishing a transformation protocol for a given plant species. As the promoter controls expression level of the genes, the promoter driving the selectable marker gene can affect transformation. However, investigations into the direct effect of promoters driving selectable marker on transformation are lacking in the literature though many reports of relative strengths of promoters driving reporter genes like GUS or CAT or GFP are available. In the present study, we have compared rice Actin1 and CaMV.35S (commonly used promoters in monocotyledonous plant transformation) promoters driving nptII for their effectiveness in paromomycin selection of transgenic corn events. To enable statistically meaningful analysis of the results, a large sample size of nearly 5,000 immature embryos (explants) was employed producing approximately 1,250 independent events from each of the two constructs in four independent experiments. The rate of appearance of resistant calli and percentage of resistant calli recovered was higher with P-Os.Actin1/nptII/nos3' as compared to P-CaMV.35S/nptII/nos3' in all four experiments. There was no appreciable difference either in the frequency of plant regeneration or in the morphological characteristics of plants recovered from the two constructs. Although the escape rate trended lower with P-Os.Actin1 as compared to P-CaMV.35S, the recovery of low copy events was significantly higher with P-CaMV.35S. The higher transformation frequency with P-Os.Actin1 could be related to the strength of this promoter as compared to P-CaMV.35S in the explants and/or calli. Based on these results, we infer that the promoter driving the selectable marker is an important factor to be considered while establishing a high throughput transformation protocol as it could not only influence the transformation frequency but also the copy number of the transgene in the recovered transgenics.

A bioinformatic approach to the identification of a conserved domain in a sugarcane legumain that directs GFP to the lytic vacuole

Sugarcane is an ideal candidate as a biofactory for the production of alternate higher value products. One way of achieving this is to direct useful proteins into the vacuoles within the sugarcane storage parenchyma tissue. By bioinformatic analysis of gene sequences from putative sugarcane vacuolar proteins a motif has been identified that displays high conservation across plant legumain homologues that are known to function within vacuolar compartments. This five amino acid motif, represented by the sequence IRLPS in sugarcane is shown to direct an otherwise secreted GFP fusion protein into a large acidic and proteolytic vacuole in sugarcane callus cells as well as in diverse plant species. In mature sugarcane transgenic plants, the stability of GFP appeared to be dependent on cell type, suggesting that the vacuolar environment can be hostile to introduced proteins. This targeting motif will be a valuable tool for engineering plants such as sugarcane for production of novel products.

Synthetic promoters: genetic control through cis engineering

Technological advances in plant genetics integrated with systems biology and bioinformatics has yielded a myriad of novel biological data and insights into plant metabolism. This unprecedented advance has provided a platform for targeted manipulation of transcriptional activity through synthetic promoter engineering, and holds great promise as a way to further our understanding of regulatory complexity. The challenge and strategy for predictive experimental gene expression is the accurate design and use of molecular 'switches' and modules that will regulate single or multiple plant transgenes in direct response to specific environmental, physiological and chemical cues. In particular, focusing on cis-motif rearrangement, future plant biotechnology applications and the elucidation of cis- and trans-regulatory mechanisms could greatly benefit from using plant synthetic promoters.

Production of polyhydroxybutyrate in sugarcane

We report here the production of the bacterial polyester, polyhydroxybutyrate (PHB), in the crop species sugarcane (Saccharum spp. hybrids). The PHB biosynthesis enzymes of Ralstonia eutropha [beta-ketothiolase (PHAA), acetoacetyl-reductase (PHAB) and PHB synthase (PHAC)] were expressed in the cytosol or targeted to mitochondria or plastids. PHB accumulated in cytosolic lines at trace amounts, but was not detected in mitochondrial lines. In plastidic lines, PHB accumulated in leaves to a maximum of 1.88% of dry weight without obvious deleterious effects. Epifluorescence and electron microscopy of leaf sections from these lines revealed that PHB granules were visible in plastids of most cell types, except mesophyll cells. The concentration of PHB in culm internodes of plastidic lines was substantially lower than in leaves. Western blot analysis of these lines indicated that expression of the PHB biosynthesis proteins was not limiting in culm internodes. Epifluorescence microscopy of culm internode sections from plastidic lines showed that PHB granules were visible in most cell types, except photosynthetic cortical cells in the rind, and that the lower PHB concentration in culm internodes was probably a result of dilution of PHB-containing cells by the large number of cells with little or no PHB. We discuss strategies for producing PHB in mitochondria and mesophyll cell plastids, and for increasing PHB yields in culms.

Refining the application of direct embryogenesis in sugarcane: Effect of the developmental phase of leaf disc explants and the timing of DNA transfer on transformation efficiency

A rapid in vitro protocol using direct somatic embryogenesis and microprojectile bombardment was investigated to establish the developmental phases most suitable for efficient sugarcane transformation. Immature leaf roll disc explants with and without pre-emergent inflorescence tissue were compared. It was shown that for effective transformation to occur, explants should be cultured for several days to allow initiation of embryo development prior to bombardment. Leaf roll discs with pre-emergent inflorescences showed a higher degree of embryogenic competence than non-flowering explants, and transformation efficiency was higher when explants containing floral initials were bombarded. Despite the occurrence of high numbers of phenotypically negative plants, combining the use of inflorescent leaf roll discs with direct embryogenic regeneration has the potential to improve the speed and efficiency of transgenesis in sugarcane.

Comparison of four constitutive promoters for the expression of transgenes in the tropical nitrogen-fixing tree Allocasuarina verticillata

Allocasuarina verticillata is an actinorhizal tree that lives in symbiotic association with a nitrogen fixing actinomycete called Frankia. In the search for promoters that drive strong constitutive expression in this tropical tree, we studied the organ specificity of four different constitutive promoters (CaMV 35S, e35S, e35S-4ocs and UBQ1 from Arabidopsis thaliana) in stably transformed A. verticillata plants. The ss-glucuronidase (gus) gene was used as a reporter and expression studies were carried out by histochemical analyses on shoots, roots and actinorhizal nodules. While the 35S promoter was poorly expressed in the shoot apex and lateral roots, both the e35S and e35S-4ocs were found to drive high constitutive expression in the transgenic non-nodulated plants. In contrast, the UBQ1 promoter was very poorly expressed and appeared unsuitable for A. verticillata. We also showed that none of the promoters studied were active in the nodule infected cells, whatever the developmental stage studied.

Gene silencing studies in the gymnosperm species Pinus radiata

A biolistic transformation procedure was used to transform embryogenic Pinus radiata tissue with constructs containing the Zea mays UBI1 (ubiquitin)-promoter followed by the P. radiata CAD (cinnamyl alcohol dehydrogenase) cDNA in sense or anti-sense orientation or in the form of an inverted-repeat. The effect of the different constructs on silencing the endogenous CAD gene was monitored in embryogenic tissue and somatic seedlings of 28 P. radiata transclones. Quantitative CAD measurements demonstrated that the construct containing an inverted-repeat of the CAD cDNA was most efficient in triggering gene silencing in P. radiata. Northern hybridization experiments with silenced transclones revealed that reduced CAD activities were the result of reduced steady state levels of the targeted CAD mRNA. Monitoring of the activity of the UBI1-promoter in the P. radiata transclones and heat-shock experiments with transgenic somatic P. radiata seedlings indicated that gene silencing is positively correlated with the expression level of the transgene. The obtained data are also consistent with a role for the expression level of the endogenous CAD gene in gene silencing.

Insect-resistant transgenic Pinus radiata

Transgenic radiata pine (Pinus radiata D. Don) plants containing a Bacillus thuringiensis (Bt) toxin gene, crylAc, were produced by means of biolistic transformation of embryogenic tissue. Using the selectable marker gene nptII and corresponding geneticin selection, 20 independent transgenic lines from five genotypes were established. Over 200 plants regenerated from ten transgenic lines were successfully transferred to soil. The integration and expression of the introduced genes in transgenic tissue and/or plants were confirmed by PCR, Southern hybridisation and neomycin phosphotransferase II (NPTII) and Bt ELISA assays. Bioassays with larvae of the painted apple moth, Teia anartoides, demonstrated that transgenic plants displayed variable levels of resistance to insect damage, with one transgenic line being highly resistant to feeding damage.

Effects of tissue culture, biolistic transformation, and introduction of PPO and SPS gene constructs on performance of sugarcane clones in the field

Stably transformed sugarcane plants were produced by the biolistic introduction of DNA into tissue-cultured cells. Constructs containing genes in sense and antisense orientation of polyphenol oxidase and sense orientation of sucrose phosphate synthase were used in the transformations. Regenerated plants were grown in a series of field experiments that incorporated commercial varieties, including Q117, from which the transgenic clones were derived and plants regenerated from tissue culture but not subjected to biolistic bombardment. In all experiments, the mean yield of transgenic sugarcane was lower than commercial varieties and the transgenic clones often exhibited lower sugar content, although individual transgenic clones in some experiments were not significantly different from Q117. Those plants regenerated from tissue culture but not bombarded were intermediate in their yield, and more clones were equivalent to Q117 in agronomic performance. Transformed plants produced by the bombardment of callus performed poorly but the results from the tissue-cultured controls indicated that not all of this could be due to somaclonal variation. Some aspect(s) of the process of transformation itself was deleterious and in most cases more significant than the effects due to tissue culture. Of the transgenic clones grown at Ayr, Queensland, 1.6% were equivalent to Q117 in sugar content and yield, suggesting that large numbers of transgenic clones would have to be generated using the current method in order to allow for selection of clones with acceptable agronomic performance.

Efficient developmental mis-targeting by the sporamin NTPP vacuolar signal to plastids in young leaves of sugarcane and Arabidopsis

Plant vacuoles are multi-functional, developmentally varied and can occupy up to 90% of plant cells. The N-terminal propeptide (NTPP) of sweet potato sporamin and the C-terminal propeptide (CTPP) of tobacco chitinase have been developed as models to target some heterologous proteins to vacuoles but so far tested on only a few plant species, vacuole types and "payload" proteins. Most studies have focused on lytic and protein-storage vacuoles, which may differ substantially from the sugar-storage vacuoles in crops like sugarcane. Our results extend the evidence that NTPP of sporamin can direct heterologous proteins to vacuoles in diverse plant species and indicate that sugarcane sucrose-storage vacuoles (like the lytic vacuoles in other plant species) are hostile to heterologous proteins. A low level of cytosolic NTPP-GFP (green fluorescent protein) was detectable in most cell types in sugarcane and Arabidopsis, but only Arabidopsis mature leaf mesophyll cells accumulated NTPP-GFP to detectable levels in vacuoles. Unexpectedly, efficient developmental mis-trafficking of NTPP-GFP to chloroplasts was found in young leaf mesophyll cells of both species. Vacuolar targeting by tobacco chitinase CTPP was inefficient in sugarcane, leaving substantial cytoplasmic activity of rat lysosomal beta-glucuronidase (GUS) [ER (endoplasmic reticulum)-RGUS-CTPP]. Sporamin NTPP is a promising targeting signal for studies of vacuolar function and for metabolic engineering. Such applications must take account of the efficient developmental mis-targeting by the signal and the instability of most introduced proteins, even in "storage vacuoles".

A variable region of the sugarcane bacilliform virus (SCBV) genome can be used to generate promoters for transgene expression in sugarcane

Four promoters derived from sugarcane bacilliform virus (SCBV) were compared and characterised. Three were obtained by PCR amplification of purified virion DNA extracted from three sugarcane cultivars. The fourth promoter was obtained by subcloning from an almost genome-length clone of SCBV. All promoters were able to drive stable expression of beta-glucuronidase in sugarcane. The PCR-derived promoter sequences shared more DNA homology with banana streak virus than to the subcloned SCBV. The subcloned promoter was the strongest expressing and was able to drive reporter gene expression in vitro and in the leaves, meristems and roots of glasshouse-grown sugarcane. Expression levels were at least equal to or higher than those measured for the maize polyubiquitin promoter.

Expression of the dihydroflavonol reductase gene in an anthocyanin-free barley mutant

The barley gene encoding dihydroflavonol-4-reductase (DFR) was delivered by micoprojectile bombardment into leaf sheath tissue of the anthocyanin-free barley mutant ant 18-162, a mutant which lacks DFR activity-probably because of a missense mutation in the structural gene for DFR. The delivered gene complemented the mutation, as evidenced by the synthesis of anthocyanin in individual leaf sheath cells of the bombarded tissues. Pigment synthesis appeared two days after gene delivery and both the number of pigmented cells and the intensity of pigmentation increased over the following days. Depending on the physiological condition of the host plants, up to 15 pigmented cells per 10 tissue segments were detected. These results demonstrate that the Ant 18 gene of barley encodes dihydroflavonol-4-reductase. A series of gene constructs encoding DFR were expressed in the anthocyanin-free mutant tissue. The genomic clone complemented the mutation whereas an equivalent plasmid with all introns deleted did not. The highest number of pigmented cells was obtained using plasmids containing the DFR-coding sequence interrupted by intron 1 of the genomic clone, indicating that the presence of an intron stabilizes the DFR message.

Comparative expression analysis of two sugarcane polyubiquitin promoters and flanking sequences in transgenic plants

GUS (uidA) reporter gene expression for two sugarcane polyubiquitin promoters, ubi4 and ubi9, was compared to expression from the maize Ubi-1 promoter in stable transgenic rice (only ubi9) and sugarcane (ubi4 and ubi9). Ubi9 drove high-level GUS expression, comparable to the maize Ubi-1 promoter, in both callus and regenerated plants of rice transformed by Agrobacterium. This high level expression was inherited in R1 plants. Expression from ubi4 and ubi9 was quite high in sugarcane callus transformed via particle bombardment. Expression dropped to very low or undetectable levels in the resulting plants; this drop in expression resulted from PTGS. PTGS in regenerated sugarcane plants also occurred with the maize Ubi-1 promoter. In sugarcane callus, ubi4 was HS inducible, but ubi9 was not. This physiological difference corresponds to a MITE insertion that is present in the putative HSEs of ubi9 but not present in ubi4.

Strategies for development of functionally equivalent promoters with minimum sequence homology for transgene expression in plants: cis-elements in a novel DNA context versus domain swapping

The cauliflower mosaic virus 35S (35S) promoter has been extensively used for the constitutive expression of transgenes in dicotyledonous plants. The repetitive use of the same promoter is known to induce transgene inactivation due to promoter homology. As a way to circumvent this problem, we tested two different strategies for the development of synthetic promoters that are functionally equivalent but have a minimum sequence homology. Such promoters can be generated by (a) introducing known cis-elements in a novel or synthetic stretch of DNA or (b) "domain swapping," wherein domains of one promoter can be replaced with functionally equivalent domains from other heterologous promoters. We evaluated the two strategies for promoter modifications using domain A (consisting of minimal promoter and subdomain A1) of the 35S promoter as a model. A set of modified 35S promoters were developed whose strength was compared with the 35S promoter per se using beta-glucuronidase as the reporter gene. Analysis of the expression of the reporter gene in transient assay system showed that domain swapping led to a significant fall in promoter activity. In contrast, promoters developed by placing cis-elements in a novel DNA context showed levels of expression comparable with that of the 35S. Two promoter constructs Mod2A1T and Mod3A1T were then designed by placing the core sequences of minimal promoter and subdomain A1 in divergent DNA sequences. Transgenics developed in tobacco (Nicotiana tabacum) with the two constructs and with 35S as control were used to assess the promoter activity in different tissues of primary transformants. Mod2A1T and Mod3A1T were found to be active in all of the tissues tested, at levels comparable with that of 35S. Further, the expression of the Mod2A1T promoter in the seedlings of the T1 generation was also similar to that of the 35S promoter. The present strategy opens up the possibility of creating a set of synthetic promoters with minimum sequence homology and with expression levels comparable with the wild-type prototype by modifying sequences present between cis-elements for transgene expression in plants.

Rice alpha-amylase transcriptional enhancers direct multiple mode regulation of promoters in transgenic rice

Expression of alpha-amylase genes in cereals is induced by both gibberellin (GA) and sugar starvation. In a transient expression assay, a 105-bp sugar response sequence (SRS) in the promoter of a sugar starvation highly inducible rice alpha-amylase gene, alphaAmy3, was shown previously to confer sugar response and to enhance the activity of the rice Act1 promoter in rice protoplasts. A 230-bp SRS-like sequence was also found in the promoter of another sugar starvation highly inducible rice alpha-amylase gene, alphaAmy8. The alphaAmy8 SRS contains a GA response sequence and was designated as alphaAmy8 SRS/GARS. In the present study, a transgenic approach was employed to characterize the function of the alpha-amylase gene SRSs in rice. We found that the alphaAmy3 SRS significantly enhances the endogenous expression pattern of the Act1 promoter in various rice tissues throughout their developmental stages. By contrast, the alphaAmy8 SRS/GARS significantly enhances Act1 promoter activity only in embryos and endosperms of germinating rice seeds. A minimal promoter fused to the alphaAmy8 SRS/GARS is specifically active in rice embryo and endosperm and is subject to sugar repression and GA induction in rice embryos. This sugar repression was found to override GA induction of alphaAmy8 SRS/GARS activity. Our study demonstrates that the alpha-amylase transcriptional enhancers contain cis-acting elements capable of enhancing endogenous expression patterns or activating sugar-sensitive, hormone-responsive, tissue-specific, and developmental stage-dependent expression of promoters in transgenic rice. These enhancers may facilitate the design of highly active and tightly regulated composite promoters for monocot transformation and gene expression. Our study also reveals the existence of cross-talk between the sugar and GA signaling pathways in cereals and provides a system for analyzing the underlying molecular mechanisms involved.

Replication-independent assembly of an insect virus (Tetraviridae) in plant cells

Infectious virions of the insect RNA virus Helicoverpa armigera stunt virus (HaSV; Omegatetravirus, Tetraviridae) were assembled in cultured plant protoplasts of Nicotiana plumbaginifolia in the absence of detectable replication. Assembly of the virus, which has not been grown in cell culture, required cotransfection of a DNA plasmid expressing the HaSV capsid gene in combination with either genomic RNA or with DNA plasmids carrying the complete cDNAs to the two HaSV genomic RNAs. Each cDNA was placed under the control of the cauliflower mosaic virus 35S promoter and followed by a cis-acting ribozyme so that the resultant transcripts corresponded precisely to the two genomic RNAs. Protoplast assembly of infectious particles was confirmed by EM and bioassay of host insect larvae, which became diseased and produced virus particles confirmed as HaSV. Variant transcripts carrying nonviral sequences at either or both termini of the RNAs showed no infectivity, except for RNA2 carrying only a 3' terminal extension. No replication of HaSV in protoplasts was detected in pulse-labeling and blotting experiments. Insects showed less severe disease symptoms when fed protoplasts transfected with only the RNA1 and coat protein plasmids. The symptomatic larvae contained only RNA1 and failed to yield infectious progeny virus, suggesting that RNA1 is capable of self-replication. This novel plasmid-based system confirms that the reported sequence of HaSV represents an infective genome and establishes a procedure for the reverse genetics of a tetravirus.

Transformation of barley by microinjection into isolated zygote protoplasts

Barley zygote protoplasts were mechanically isolated, embedded in agarose droplets, and microinjected with a rice actin promoter Act1-gusA-nos gene construct. On average 62% of the cells survived the injection and of these 55% continued development into embryo-like structures and eventually to plants. PCR screening for the presence of a 307-bp fragment in the middle of the gusA gene showed that on average 21% of the derived structures contained this fragment. However, among the hundreds of injected zygotes, derived structures and regenerants we only found significant GUS expression in two cases (embryo-like structures nine days after injection). Two lines of green plants, derived from zygotes microinjected with linearized plasmid (line A147-1) or an isolated Act1-gusA-nos gene cassette (line A166-h) proved to be transgenic. Line A147-1 appeared to contain a single and intact copy of the expression cassette but a PCR based progeny analysis indicated the presence of additional shorter fragments of the cassette. Line A166-h appeared to contain a single fragment of the gusA gene that was transferred to the progeny as a single Mendelian trait. One additional fragment of the gusA gene was identified in this line. The present data show that transformation of barley by microinjection of DNA into isolated zygotes is feasible but also that gene expression rarely is achieved, possibly due to degradation of the introduced DNA.

Chromosome-mediated and direct gene transfers in wheat

Wild grasses, including relatives of wheat, have several desirable characters that can be introduced into both bread wheat and durum wheat. Since current wheat cultivars lack certain traits, for example, resistance to fusarium head blight (scab), related wild grasses may be the only option for useful variability. Wide hybridization of wheat with grasses, coupled with cytogenetic manipulation of the hybrid material, has been instrumental in the genetic improvement of wheat. Chromosome engineering methodologies, based on the manipulation of pairing control mechanisms and induced translocations, have been employed to transfer into wheat specific disease and pest resistance genes from annual (e.g., rye) or perennial (e.g., Thinopyrum spp., Lophopyrum spp., and Agropyron spp.) members of the wheat tribe, Triticeae. The advent of in situ hybridization techniques, for example, fluorescent GISH combined with Giemsa C-banding, has proved immensely useful in characterizing alien chromatin specifying resistance to various pathogens and pests. The use of DNA markers (RAPDs and RFLPs) helps to identify desirable genotypes more precisely and, thereby, facilitates gene transfer into wheat. Such markers may be particularly helpful in monitoring the introgression of alien genes in the wheat genome. In fact, several cultivars, particularly of bread wheat, contain superior traits of alien origin. The development of novel gene-transfer techniques in the past decade that allow direct delivery of DNA into regenerable embryogenic callus of wheat has opened up new avenues of alien-gene transfer into wheat cultivars. Thus, transgenic bread and durum wheats have been produced and methods of gene delivery standardized. The application of transgenic technology has not only yielded herbicide-resistant wheats, but has also helped to improve grain quality by modifying the protein and starch profiles of the grain. These in vitro approaches to gene transfer are developing rapidly, and promise to become an integral part of plant breeding efforts. However, the new biotechnological tools will complement, not replace, conventional plant breeding.Key words: alien-gene transfer, fluorescent GISH, Giemsa banding, homoeologous chromosome pairing, molecular markers, transgenic bread wheat, transgenic durum wheat.

Herbicide resistance caused by spontaneous mutation of the cytoskeletal protein tubulin

The dinitroaniline herbicides (such as trifluralin and oryzalin) have been developed for the selective control of weeds in arable crops. However, prolonged use of these chemicals has resulted in the selection of resistant biotypes of goosegrass, a major weed. These herbicides bind to the plant tubulin protein but not to mammalian tubulin. Here we show that the major alpha-tubulin gene of the resistant biotype has three base changes within the coding sequence. These base changes swap cytosine and thymine, most likely as the result of the spontaneous deamination of methylated cytosine. One of these base changes causes an amino-acid change in the protein: normal threonine at position 239 is changed to isoleucine. This position is close to the site of interaction between tubulin dimers in the microtubule protofilament. We show that the mutated gene is the cause of the herbicide resistance by using it to transform maize and confer resistance to dinitroaniline herbicides. Our results provide a molecular explanation for the resistance of goosegrass to dinitroanaline herbicides, a phenomenon that has arisen, and been selected for, as a result of repeated exposure to this class of herbicide.

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.

Engineering of the aspartate family biosynthetic pathway in barley (Hordeum vulgare L.) by transformation with heterologous genes encoding feed-back-insensitive aspartate kinase and dihydrodipicolinate synthase

In prokaryotes and plants the synthesis of the essential amino acids lysine and threonine is predominantly regulated by feed-back inhibition of aspartate kinase (AK) and dihydrodipicolinate synthase (DHPS). In order to modify the flux through the aspartate family pathway in barley and enhance the accumulation of the corresponding amino acids, we have generated transgenic barley plants that constitutively express mutant Escherichia coli genes encoding lysine feed-back insensitive forms of AK and DHPS. As a result, leaves of primary transformants (T0) exhibited a 14-fold increase of free lysine and an 8-fold increase in free methionine. In mature seeds of the DHPS transgenics, there was a 2-fold increase in free lysine, arginine and asparagine and a 50% reduction in free proline, while no changes were observed in the seeds of the two AK transgenic lines analysed. When compared to that of control seeds, no differences were observed in the composition of total amino acids. The introduced genes were inherited in the T1 generation where enzymic activities revealed a 2.3-fold increase of AK activity and a 4.0-9.5-fold increase for DHPS. T1 seeds of DHPS transformants showed the same changes in free amino acids as observed in T0 seeds. It is concluded that the aspartate family pathway may be genetically engineered by the introduction of genes coding for feed-back-insensitive enzymes, preferentially giving elevated levels of lysine and methionine.

Intron-specific stimulation of anaerobic gene expression and splicing efficiency in maize cells

Most of the glyceraldehyde-3-phosphate dehydrogenase (GAPDH) genes characterized in plants and algae to date have one intron very close to the 5' end of the gene. To study the functional relevance of some of these introns for gene expression we have analysed the influence of three 5' introns on transient gene expression of the anaerobically inducible maize GapC4 promoter in maize cells. Under aerobic conditions, reporter gene expression is increased in the presence of the first introns of the GapC4 and GapC1 genes, and the first intron of the nuclear encoded chloroplast-specific GapA1 gene. In contrast, the GapC4 intron increases anaerobic gene expression above the level obtained for the intronless construct, while anaerobic expression of constructs harboring the GapA1 and GapC1 introns was similar to the anaerobic expression level of the intronless construct. Splicing analysis revealed that the GapC4 intron is processed more efficiently under anaerobic conditions, while no change in splicing efficiency is observed for the GapC1 and the GapA1 introns when subjected to anaerobic conditions. These results suggest that an increase in splicing efficiency contributes to the anaerobic induction of the maize GapC4 gene.

Hordein promoter methylation and transcriptional activity in wild-type and mutant barley endosperm

B- and C-hordein gene transcription is severely reduced in the endosperm of the regulatory barley mutant lys3a, and this is correlated with persistent hypermethylation of the promoters. In contrast, D-hordein is expressed at normal levels in the mutant. To confirm the connection between methylation and transcriptional activity, a genomic D-hordein clone was isolated and sequenced. The nucleotide composition of the promoter region revealed a CpG island and methylation analysis, using bisulphite treatment of genomic DNA, confirmed that the D-hordein promoter is unmethylated in endosperm and leaf tissue. Immunocytochemical studies localized D-hordein to the reticular component of protein bodies in both the wild-type Bomi and lys3a. Transient expression of GUS reporter gene constructs in barley endosperm, following transfection by particle bombardment revealed the D-hordein promotors. Comparison of transient expression in Bomi and lys3a endosperm demonstrated that the activities of the unmethylated D-hordein and the Hor1-14 C-hordein promoters were equivalent, while the activities in the mutant of the Horl-17 C-hordein and the Hor2-4 B-hordein promoters were reduced two- and tenfold, respectively. Methylation of plasmids in vitro prior to expression severely inhibited B- and D-hordein promoter activities. Based on these observations two categories of promoters for endosperm-specific expression of storage proteins are recognized and a model involving methylation and modulation of chromatin structure in the regulation by the Lys3 gene is presented.

Expression, purification, and use as an antigen of recombinant sugarcane mosaic virus coat protein

A high titre (1:10,000) antiserum was raised in a rabbit against the coat protein of sugarcane mosaic potyvirus (SCMV), by injecting a preparation of recombinant coat protein purified from a fusion protein expressed in E. coli. The fusion protein consisted of the MalE maltose binding protein (MBP) and the viral coat protein separated by the protease factor Xa cleavage site. The fusion protein was encoded by the plasmid pMAL-cCPM, which was constructed by cloning a modified coat protein gene to the 3' end of the MBP/factor Xa coding region. The coat protein gene was modified by site-directed mutagenesis so that the ATG start codon in the original construct was replaced by the codon AGC, deleting the NcoI restriction site (C/CATGG) and creating a unique Eco47III site (AGC/GCT). Endonuclease restriction with Eco47III resulted in a DNA fragment with GCT as the first three nucleotides. This triplet encodes alanine, which is the proposed N-terminal amino acid residue of the mature native coat protein. This modified coat protein coding region was ligated directly behind the nucleotide code for the amino acid recognition sequence for factor Xa. Expression was induced with IPTG and the recombinant fusion protein was extracted from the bacterial lysate by amylose resin column affinity chromatography and the two domains separated by factor Xa proteolysis. The coat protein was then purified from the maltose binding protein by ion exchange chromatography in buffer containing 6 M urea. A highly purified sample which contained 150 micrograms of both full-length and truncated coat proteins, was recovered from a litre of bacterial broth. The antiserum reacted with native coat protein in SCMV-infected sugarcane, and with recombinant coat proteins expressed in E. coli and sugarcane protoplasts with little or no cross-reaction with sugarcane proteins.

Adenine methylation at dam sites increases transient gene expression in plant cells

Escherichia coli encodes two major DNA methylation systems: dam, which produces 6-methyladenine; and dcm, which produces 5-methylcytosine. About 1-2% of adenine and cytosine residues in plasmid DNAs prepared in E. coli are methylated by these systems. Since DNA methylation profoundly influences gene expression in eukaryotes, we were interested in determining whether these bacterially encoded modifications might also effect plant gene expression in experimental systems. We therefore examined the influence of dam and dcm methylation on gene expression from four GUS fusion constructs in transient assays in protoplasts and microprojectile-bombarded whole tissues. In these constructs, GUS expression was driven by promoter regions derived from the Arabidopsis alcohol dehydrogenase (Adh1), maize ubiquitin (Ubi1), rice actin (Act1) and CaMV 35S genes. We show that methyladenine produced by dam methylation increased gene expression from constructs based on the Adh1, Ubi1 and Act1 genes. The increase in gene expression ranged from three-fold for Ubi1 and Adh1 in protoplasts to 50-fold for Act1 in bombarded wheat tissues. Expression of a 35S.GUS construct was, however, insensitive to dam methylation. dcm methylation had little if any effect on transient gene expression for any of these constructs. We provide indirect evidence that the critical sites of adenine methylation lie within sequences from the promoter regions, suggesting that dam methylation increases transcription rate. These results have important experimental implications and also raise the intriguing possibility that methyladenine might play a role in the regulation of gene expression in vivo.

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.