Identification of different agrobacterium strains isolated from the same forest nursery

Several Agrobacterium strains isolated from the same forest nursery from 1982 to 1988 were compared by serological, biochemical, and DNA-DNA hybridization methods. Similarities among strains belonging to biovar 2 were observed by indirect immunofluorescence, whereas biovar 1 strains showed serological heterogeneity. Electrophoretic analysis of bacterial envelope-associated proteins showed that few bands appeared in the strains belonging to biovar 1, whereas many proteins appeared in the case of biovar 2 strains. Chromosomal DNA was analyzed with six random C58 chromosomal fragments. None of the six probes hybridized to the DNA of the two biovar 2 strains. One of the probes gave the same hybridization pattern with all biovar 1 strains, whereas the other probes yielded different patterns. The vir regions were closely related in the different pathogenic strains. The T-DNA and replication regions were less conserved and showed some variations among the strains.

Eucalyptus gunnii CCR and CAD2 promoters are active in lignifying cells during primary and secondary xylem formation in Arabidopsis thaliana

Cell-specific expression patterns of the Eucalyptus gunnii cinnamoyl coenzymeA reductase (EgCCR) and cinnamyl alcohol dehydrogenase (EgCAD2) promoters were analyzed by promoter-GUS histochemistry in the primary and secondary xylem tissues from floral stems and roots of Arabidopsis thaliana. Expression patterns indicated that the EgCCR and EgCAD2 genes were expressed in a coordinated manner in primary and secondary xylem tissues of the Arabidopsis floral stem and root. Both genes were expressed in all lignifying cells (vessel elements, xylem fibers and paratracheal parenchyma cells) of xylem tissues. The capacity for long-term monolignol production appeared to be related to the cell-specific developmental processes and biological roles of different cell types. Our results suggested that lignification of short-lived vessel elements was achieved by a two-step process involving (i) monolignol production by vessel elements prior to vessel programmed cell death and (ii) subsequent monolignol production by vessel-associated living paratracheal parenchyma cells following vessel element cell death. EgCCR and EgCAD2 gene expression patterns suggested that the process of xylem cell lignification was similar in both primary and secondary xylem tissues in Arabidopsis floral stems and roots.

Plant glycoside hydrolases involved in cell wall polysaccharide degradation

The cell wall plays a key role in controlling the size and shape of the plant cell during plant development and in the interactions of the plant with its environment. The cell wall structure is complex and contains various components such as polysaccharides, lignin and proteins whose composition and concentration change during plant development and growth. Many studies have revealed changes in cell walls which occur during cell division, expansion, and differentiation and in response to environmental stresses; i.e. pathogens or mechanical stress. Although many proteins and enzymes are necessary for the control of cell wall organization, little information is available concerning them. An important advance was made recently concerning cell wall organization as plant enzymes that belong to the superfamily of glycoside hydrolases and transglycosidases were identified and characterized; these enzymes are involved in the degradation of cell wall polysaccharides. Glycoside hydrolases have been characterized using molecular, genetic and biochemical approaches. Many genes encoding these enzymes have been identified and functional analysis of some of them has been performed. This review summarizes our current knowledge about plant glycoside hydrolases that participate in the degradation and reorganisation of cell wall polysaccharides in plants focussing particularly on those from Arabidopsis thaliana.

Genetic variations of cell wall digestibility related traits in floral stems of Arabidopsis thaliana accessions as a basis for the improvement of the feeding value in maize and forage plants

Floral stems of Arabidopsis thaliana accessions were used as a model system relative to forage plant stems in genetic variation studies of lignin content and cell wall digestibility related traits. Successive investigations were developed in a core collection of 24 Arabidopsis accessions and in a larger collection of 280 accessions. Significant genetic variation for lignin content in the cell wall, and for the two in vitro cell wall digestibility investigated traits, were found both in the core collection and in the large collection. Genotype x environment interactions, investigated in the core collection, were significant with a few genotypes contributing greatly to interactions, based on ecovalence value estimates. In the core collection, genotypes 42AV, 224AV, and 8AV had low cell wall digestibility values, whatever be the environmental conditions. Genotype 157AV, observed only in one environment, also appeared to have a low cell wall digestibility. Conversely, genotypes 236AV, 162AV, 70AV, 101AV, 83AV had high cell wall digestibility values, genotype 83AV having a slightly greater instability across differing environments than others. The well-known accession Col-0 (186AV) appeared with a medium level of cell wall digestibility and a weak to medium level of interaction between environments. The ranges of variation in cell wall digestibility traits were higher in the large collection than in the core collection of 24 accessions, these results needing confirmation due to the lower number of replicates. Accessions 295AV, 148AV, and 309AV could be models for low stem cell wall digestibility values, with variable lignin content. Similarly, accessions 83AV and 162AV, already identified from the study of the core collection, and five accessions (6AV, 20AV, 91AV, 114AV, and 223AV) could be models for high stem cell wall digestibility values. The large variations observed between Arabidopsis accessions for both lignin content and cell wall digestibility in floral stems have strengthened the use this species as a powerful tool for discovering genes involved in cell wall biosynthesis and lignification of dicotyledons forage plants. Investigations of this kind might also be applicable to monocotyledons forage plants due to the basic similarity of the genes involved in the lignin pathway of Angiosperms and the partial homology of the cell wall composition and organization of the mature vascular system in grasses and Arabidopsis.

Potential effects of plant protease inhibitors, oryzacystatin I and soybean Bowman-Birk inhibitor, on the aphid parasitoid Aphidius ervi Haliday (Hymenoptera, Braconidae)

Protease inhibitors (PIs) have been shown to cause lethal and sublethal effects on aphids depending on the kind of PI and aphid species. Therefore, these proteins might affect aphid parasitoids directly by inhibiting their digestive proteolysis or indirectly via their development in a less suitable host. In our study, the risk of exposure and the potential effects of soybean Bowman-Birk inhibitor (SbBBI) and oryzacystatin I (OCI) on the aphid endoparasitoid Aphidius ervi were investigated using artificial diet to deliver PIs. Immunoassays showed that both SbBBI and OCI were detected in the honeydew of aphids reared on artificial diet containing these recombinant proteins at 100 microg/mL. However, only SbBBI was detected in parasitoid larvae, while this PI could not be detected in adult parasitoids emerged from PI-intoxicated aphids. Enzymatic inhibition assays showed that digestive proteolytic activity of larvae and adults of A. ervi predominantly relies on serine proteases and especially on chymotrypsin-like activity. Bioassays using SbBBI and OCI on artificial diet were performed. A. ervi that developed on intoxicated aphids had impaired fitness. Thus development and parasitism success of parasitoids exposed to OCI were severely affected. On the contrary, SbBBI only altered significantly female size and sex ratio. Direct exposure to PIs through adult food intake did not affect female's longevity, while SbBBI and OCI (100 microg/mL) induced 69% and 30% inhibition of digestive protease activity, respectively. These studies made it possible to estimate the risk of exposure to plant PIs and the sensitivity of the aphid parasitoid A. ervi to these entomotoxins, by combining immunological, biochemical and biological approaches. First it pointed out that only immature stages are affected by PIs. Secondly, it documented two different modes of effect, according to the nature of the PIs and both host and parasitoid susceptibility. OCI prevented the development of A. ervi mainly due to the host susceptibility, whereas SbBBI only induced sublethal effects on the parasitoid, possibly due to both direct action on the parasitoid susceptible proteases, and host-mediated action through size reduction.

Effects of plant protease inhibitors, oryzacystatin I and soybean Bowman-Birk inhibitor, on the aphid Macrosiphum euphorbiae (Homoptera, Aphididae) and its parasitoid Aphelinus abdominalis (Hymenoptera, Aphelinidae)

Transgenic plants expressing protease inhibitors (PIs) have emerged in recent years as an alternative strategy for pest control. Beneficial insects such as parasitoids may therefore be exposed to these entomotoxins either via the host or by direct exposure to the plant itself. With the objective of assessing the effects of PIs towards aphid parasitoids, bioassays using soybean Bowman-Birk inhibitor (SbBBI) or oryzacystatin I (OCI) on artificial diet were performed on Macrosiphum euphorbiae-Aphelinus abdominalis system. OCI significantly reduced nymphal survival of the potato aphid M. euphorbiae and prevented aphids from reproducing. This negative effect was much more pronounced than with other aphid species. On the contrary, SbBBI did not affect nymphal viability but significantly altered adult demographic parameters. Enzymatic inhibition assays showed that digestive proteolytic activity of larvae and adults of Aphelinus abdominalis predominantly relies on serine proteases and especially on chymotrypsin-like activity. Immunoassays suggested that OCI bound to aphid proteins and accumulated in aphid tissues, whereas SbBBI remained unbound in the gut. Bioassays using M. euphorbiae reared on artificial diets supplemented with both OCI and SbBBI showed a fitness impairment of Aphelinus abdominalis that developed on intoxicated aphids. However, only SbBBI was detected in parasitoid larvae, while no PI could be detected in adult parasitoids that emerged from PI-intoxicated aphids. The potential impact of PI-expressing plants on aphid parasitoids and their combined efficiency for aphid control are discussed.

Impact of oilseed rape expressing the insecticidal serine protease inhibitor, mustard trypsin inhibitor-2 on the beneficial predator Pterostichus madidus

Abstract Insect-resistant transgenic plants have been suggested to have deleterious effects on beneficial predators feeding on crop pests, through transmission of the transgene product by the pest to the predator. To test this hypothesis, effects of oilseed rape expressing the serine protease inhibitor, mustard trypsin inhibitor -2 (MTI-2), on the predatory ground beetle Pterostichus madidus were investigated, using diamondback moth, Plutella xylostella as the intermediary pest species. As expected, oilseed rape expressing MTI-2 had a deleterious effect on the development and survival of the pest. However, incomplete pest mortality resulted in survivors being available to predators at the next trophic level, and inhibition studies confirmed the presence of biologically active transgene product in pest larvae. Characterization of proteolytic digestive enzymes of P. madidus demonstrated that adults utilize serine proteases with trypsin-like and chymotrypsin-like specificities; the former activity was completely inhibited by MTI-2 in vitro. When P. madidus consumed prey reared on MTI-2 expressing plants over the reproductive period in their life cycle, no significant effects upon survival were observed as a result of exposure to the inhibitor. However, there was a short-term significant inhibition of weight gain in female beetles fed unlimited prey containing MTI-2, with a concomitant reduction of prey consumption. Biochemical analyses showed that the inhibitory effects of MTI-2 delivered via prey on gut proteolysis in the carabid decreased with time of exposure, possibly resulting from up-regulation of inhibitor-insensitive proteases. Of ecological significance, consumption of MTI-2 dosed prey had no detrimental effects on reproductive fitness of adult P. madidus.

Cloning and characterization of a gut-specific cathepsin L from the aphid Aphis gossypii

We have characterized proteinase activities in gut extracts from the cotton-melon aphid (Aphis gossypii Glover), an insect feeding strictly on protein-poor phloem. The major, if not exclusive, intestinal proteinases of this aphid are of the cysteine type. A cDNA has been cloned from a gut library and codes for the cysteine proteinase AgCatL, a cathepsin L-like cysteine proteinase. The AgCatL protein shows high sequence similarity with mammalian and some arthropod cathepsin L-like proteinases, but can be reliably distinguished from the secreted (digestive) proteinases identified in other arthropods. AgCatL is widely expressed in aphid intestinal cells. Immunolocalization of AgCatL showed an intense signal at the level of the anterior 'stomach' part of the midgut, and especially at intracellular localization. Although the precise role of AgCatL in aphid midgut physiology is still unclear, this enzyme could be involved in the processing of exogenous ingested polypeptides.

Impact of oilseed rape expressing the insecticidal cysteine protease inhibitor oryzacystatin on the beneficial predator Harmonia axyridis (multicoloured Asian ladybeetle)

Insect-resistant transgenic plants have been suggested to have deleterious effects on beneficial predators through transmission of the transgene product by the pest to the predator. To test this hypothesis, effects of oilseed rape expressing the cysteine protease inhibitor oryzacystatin-1 (OC-1) on the predatory ladybird Harmonia axyridis were investigated using diamondback moth Plutella xylostella as the pest species. As expected, oilseed rape expressing OC-1 had no effects on either development or survival of the pest, which utilizes serine digestive proteases. Immunoassays confirmed accumulation of the transgene product in pest larval tissues at levels of up to 3 ng per gut. Characterization of proteolytic digestive enzymes of H. axyridis demonstrated that larvae and adults utilize cysteine and aspartic proteases; the former activity was completely inhibited by oryzacystatin in vitro. However, when H. axyridis larvae consumed prey reared on OC-1 expressing plants over their entire life cycle, no significant effects upon survival or overall development were observed. The inhibitor initially stimulated development, with a shortening of the developmental period of the second instar by 27% (P < 0.0001) accompanied by a 36% increase in weight of second instar larvae (P = 0.007). OC-1 had no detrimental effects on reproductive fitness of adult H. axyridis. Interestingly there was a significant increase in consumption of OC-1 dosed prey. The results show that prey reared on transgenic plants expressing a protein which inhibited ladybird digestive enzymes in vitro had no effects in vivo; the ladybird was able to up-regulate digestive proteases in response to the inhibitor.

Elucidation of new structures in lignins of CAD- and COMT-deficient plants by NMR

Studying lignin-biosynthetic-pathway mutants and transgenics provides insights into plant responses to perturbations of the lignification system, and enhances our understanding of normal lignification. When enzymes late in the pathway are downregulated, significant changes in the composition and structure of lignin may result. NMR spectroscopy provides powerful diagnostic tools for elucidating structures in the difficult lignin polymer, hinting at the chemical and biochemical changes that have occurred. COMT (caffeic acid O-methyl transferase) downregulation in poplar results in the incorporation of 5-hydroxyconiferyl alcohol into lignins via typical radical coupling reactions, but post-coupling quinone methide internal trapping reactions produce novel benzodioxane units in the lignin. CAD (cinnamyl alcohol dehydrogenase) downregulation results in the incorporation of the hydroxycinnamyl aldehyde monolignol precursors intimately into the polymer. Sinapyl aldehyde cross-couples 8-O-4 with both guaiacyl and syringyl units in the growing polymer, whereas coniferyl aldehyde cross-couples 8-O-4 only with syringyl units, reflecting simple chemical cross-coupling propensities. The incorporation of hydroxycinnamyl aldehyde and 5-hydroxyconiferyl alcohol monomers indicates that these monolignol intermediates are secreted to the cell wall for lignification. The recognition that novel units can incorporate into lignins portends significantly expanded opportunities for engineering the composition and consequent properties of lignin for improved utilization of valuable plant resources.

Population-scale laboratory studies of the effect of transgenic plants on nontarget insects

Studies of the effects of insect-resistant transgenic plants on beneficial insects have, to date, concentrated mainly on either small-scale "worst case scenario" laboratory experiments or on field trials. We present a laboratory method using large population cages that represent an intermediate experimental scale, allowing the study of ecological and behavioural interactions between transgenic plants, pests and their natural enemies under more controlled conditions than is possible in the field. Previous studies have also concentrated on natural enemies of lepidopteran and coleopteran target pests. However, natural enemies of other pests, which are not controlled by the transgenic plants, are also potentially exposed to the transgene product when feeding on hosts. The reduction in the use of insecticides on transgenic crops could lead to increasing problems with such nontarget pests, normally controlled by sprays, especially if there are any negative effects of the transgenic plant on their natural enemies. This study tested two lines of insect-resistant transgenic oilseed rape (Brassica napus) for side-effects on the hymenopteran parasitoid Diaeretiella rapae and its aphid host, Myzus persicae. One transgenic line expressed the delta-endotoxin Cry1Ac from Bacillus thuringiensis (Bt) and a second expressed the proteinase inhibitor oryzacystatin I (OC-I) from rice. These transgenic plant lines were developed to provide resistance to lepidopteran and coleopteran pests, respectively. No detrimental effects of the transgenic oilseed rape lines on the ability of the parasitoid to control aphid populations were observed. Adult parasitoid emergence and sex ratio were also not consistently altered on the transgenic oilseed rape lines compared with the wild-type lines.

Effects of a mustard trypsin inhibitor expressed in different plants on three lepidopteran pests

The effects of mustard trypsin inhibitor MTI-2 expressed at different levels in transgenic tobacco, arabidopsis and oilseed rape lines have been evaluated against three different lepidopteran insect pests. 1. Plutella xylostella (L.) larvae were the most sensitive to the ingestion of MTI-2. The inhibitor expressed at high levels in arabidopsis plants caused rapid and complete mortality. High mortality and significantly delayed larval development were also detectable in oilseed rape expressing MTI-2 at lower levels. 2. Mamestra brassicae (L.) larvae were sensitive only at high MTI-2 expression level, as obtained in transgenic tobacco and arabidopsis, whereas no effects were observed for larvae fed on plants showing relatively low expression levels such as those of oilseed rape lines. 3. Feeding bioassays with Spodoptera littoralis (Boisduval) larvae were carried out using the same oilseed rape lines, showing that at these low expression levels no mortality was observed although a delay in larval development did occur. The levels of insect gut proteolytic activities of the larvae still alive at the end of a 7 day feeding bioassay were usually higher than in the controls, but no new proteinases were expressed in any case. The combined results described in this paper demonstrate altogether the relevance of a case-by-case analysis [target insects and proteinase inhibitor (PI) level of expression in planta] in a PI-based strategy for plant protection.

Analysis of mustard trypsin inhibitor-2 gene expression in response to developmental or environmental induction

Transcription analysis of a mustard (Sinapis alba L.) serine proteinase inhibitor gene revealed identical 5' termini of mRNAs synthesized during seed maturation and chemical or wounding induction. Polyadenylation of mRNAs on multiple or single sites differentiated gene expression, increasing the availability of stable mRNAs during seed maturation compared with chemical and wounding induction. Expression of the beta-glucuronidase (GUS)-encoding region of the UidA reporter gene, detected under the control of deleted segments of the region flanking on the 5' side the mit-2 gene, identified a stretch of about 520 bp essential for gene expression. The presence in this region of two ABRE motifs is relevant for plant response to gene induction. Expression of GUS was detectable under different induction stimuli in several organs such as seedlings and leaves and was active to varying extents in the vascular tissues and meristem.

NMR evidence for benzodioxane structures resulting from incorporation of 5-hydroxyconiferyl alcohol into Lignins of O-methyltransferase-deficient poplars

Benzodioxane structures are produced in lignins of transgenic poplar plants deficient in COMT, anO-methyltransferase required to produce lignin syringyl units. They result from incorporation of 5-hydroxyconiferyl alcohol into the monomer supply and confirm that phenols other than the three traditional monolignols can be integrated into plant lignins.

Regulation of sulfur nutrition in wild-type and transgenic poplar over-expressing gamma-glutamylcysteine synthetase in the cytosol as affected by atmospheric H2S

This study with poplar (Populus tremula x Populus alba) cuttings was aimed to test the hypothesis that sulfate uptake is regulated by demand-driven control and that this regulation is mediated by phloem-transported glutathione as a shoot-to-root signal. Therefore, sulfur nutrition was investigated at (a) enhanced sulfate demand in transgenic poplar over-expressing gamma-glutamylcysteine (gamma-EC) synthetase in the cytosol and (b) reduced sulfate demand during short-term exposure to H2S. H(2)S taken up by the leaves increased cysteine, gamma-EC, and glutathione concentrations in leaves, xylem sap, phloem exudate, and roots, both in wild-type and transgenic poplar. The observed reduced xylem loading of sulfate after H2S exposure of wild-type poplar could well be explained by a higher glutathione concentration in the phloem. In transgenic poplar increased concentrations of glutathione and gamma-EC were found not only in leaves, xylem sap, and roots but also in phloem exudate irrespective of H(2)S exposure. Despite enhanced phloem allocation of glutathione and its accumulation in the roots, sulfate uptake was strongly enhanced. This finding is contradictory to the hypothesis that glutathione allocated in the phloem reduces sulfate uptake and its transport to the shoot. Correlation analysis provided circumstantial evidence that the sulfate to glutathione ratio in the phloem may control sulfate uptake and loading into the xylem, both when the sulfate demand of the shoot is increased and when it is reduced.

Lignification in transgenic poplars with extremely reduced caffeic acid O-methyltransferase activity

Transgenic poplars (Populus tremula x Populus alba) were obtained by introduction of a sense homologous transgene encoding caffeic acid O-methyltransferase (COMT) under the control either of the cauliflower mosaic virus double 35S promoter or of the eucalyptus cinnamyl alcohol dehydrogenase promoter. Although these constructs conferred a moderate overexpression of COMT in some lines, a transgenic line with the double 35S promoter was found where COMT activity in woody tissues was close to zero due to a gene-silencing phenomenon. For the first time in COMT down-regulated trees, this alteration substantially reduced lignin level in 6-month-old trees (17% decrease). Lignin structure was found to be strongly altered, with a two times higher content in condensed bonds, an almost complete lack of syringyl units, and the incorporation of 5-hydroxyguaiacyl units to the most remarkable extent reported so far. Consistent with the higher cellulose content and with the higher condensation degree of the lignin, the impact of the transformation on the kraft-pulping performances of the poplar trees positively affected the pulp yield (10% relative increase), but made lignins less amenable to industrial degradations.

Diverse effects of overexpression of LEAFY and PTLF, a poplar (Populus) homolog of LEAFY/FLORICAULA, in transgenic poplar and Arabidopsis

PTLF, the Populus trichocarpa homolog of LEAFY (LFY) and FLORICAULA, was cloned to assess its function in a dioecious tree species. In situ hybridization studies showed that the gene was expressed most strongly in developing inflorescences. Expression was also seen in leaf primordia and very young leaves, most notably in apical vegetative buds near inflorescences, but also in seedlings. Although ectopic expression of the PTLF cDNA in Arabidopsis accelerated flowering, only one of the many tested transgenic lines of Populus flowered precociously. The majority of trees within a population of 3-year-old transgenic hybrid Populus lines with PTLF constitutively expressed showed few differences when compared to controls. However, phenotypic effects on growth rate and crown development, but not flowering, were seen in some trees with strong PTLF expression and became manifest only as the trees aged. Competence to respond to overexpression of LFY varied widely among Populus genotypes, giving consistent early flowering in only a single male P. tremula x P. tremuloides hybrid and causing gender change in another hybrid genotype. PTLF activity appears to be subject to regulation that does not affect heterologously expressed LFY, and is dependent upon tree maturation. Both genes provide tools for probing the mechanisms of delayed competence to flower in woody plants.

Isolation and characterization of a dehydrin gene from white spruce induced upon wounding, drought and cold stresses

A cDNA clone encoding a dehydrin gene was isolated from a cDNA library prepared from white spruce (Picea glauca) needle mRNAs. The cDNA, designated PgDhn1, is 1159 nucleotides long and has an open reading frame of 735 bp with a deduced amino acid sequence of 245 residues. The PgDhn1 amino acid sequence is highly hydrophilic and possesses four conserved repeats of the characterized lysine-rich K-segment (EKKGIMD-KIKEKLPG), and an 8-serine residue stretch prior to the first lysine-rich repeat that is common to many dehydrins. The DEYGNP conserved motif is, however, absent in the PgDhn1 sequence. In unstressed plants, the highest level of transcripts was detected in stem tissue and not fully expanded vegetative buds. PgDhn1 expression was also clearly detected in reproductive buds, at various stages of development. The mRNAs corresponding to PgDhn1 cDNA were induced upon wounding and by jasmonic acid (JA) and methyl jasmonate (MeJa) treatments. Upon drought stress, increased transcript accumulation was observed in needle tissue reaching a maximum level 48 h after treatment. Treatments of seedlings with abscisic acid or ethephon also resulted in high levels of transcript accumulation in needle tissue. Finally, cold induction of PgDhn1 transcripts was also detected as early as 8 h after treatment.

Molecular cloning of cDNAs encoding a range of digestive enzymes from a phytophagous beetle, Phaedon cochleariae

To gain better knowledge of the variety of digestive enzymes in phytophagous coleopteran pests, a sequencing screen of 76 random cDNAs from a gut library from Phaedon cochleariae larvae was performed. The screen yielded 21 cDNAs encoding amino-acid sequences homologous to known digestive enzymes, most of them were cell wall-hydrolysing enzymes. The deduced protein sequences of 7 cDNAs encoding putative alpha-amylase, cysteine proteinase, trypsin, chymotrypsin, cellulase, pectinase and xylanase display all the structural features that characterize these enzymes in other eukaryotic organisms. Except the alpha-amylase and chymotrypsin cDNAs, the other cDNAs probably derive from multigene families. The distribution of the corresponding enzymatic activities at various developmental stages of P. cochleariae was examined. alpha-amylase activity is present in guts of larvae and adults, proteinases are abundant in guts of larvae and adults, but scarce in eggs and larval carcasses, xylanases are present in the guts of larvae and adults, as well as in carcasses of larvae, whereas cellulase and pectinase activities are distributed in larval and adult guts, larval carcasses, and eggs. Only a minor fraction of the cellulases is secreted by microorganisms, suggesting that P. cochleariae synthesizes most of its own cell-wall hydrolysing enzymes. The physiological role of the enzymes is discussed, as well as the significance of these results for pest management strategies involving transgenic plants expressing enzyme inhibitors.

Cadmium tolerance and accumulation in Indian mustard is enhanced by overexpressing gamma-glutamylcysteine synthetase

To investigate rate-limiting factors for glutathione and phytochelatin (PC) production and the importance of these compounds for heavy metal tolerance, Indian mustard (Brassica juncea) was genetically engineered to overexpress the Escherichia coli gshI gene encoding gamma-glutamylcysteine synthetase (gamma-ECS), targeted to the plastids. The gamma-ECS transgenic seedlings showed increased tolerance to Cd and had higher concentrations of PCs, gamma-GluCys, glutathione, and total non-protein thiols compared with wild-type (WT) seedlings. When tested in a hydroponic system, gamma-ECS mature plants accumulated more Cd than WT plants: shoot Cd concentrations were 40% to 90% higher. In spite of their higher tissue Cd concentration, the gamma-ECS plants grew better in the presence of Cd than WT. We conclude that overexpression of gamma-ECS increases biosynthesis of glutathione and PCs, which in turn enhances Cd tolerance and accumulation. Thus, overexpression of gamma-ECS appears to be a promising strategy for the production of plants with superior heavy metal phytoremediation capacity.

Isolation and characterization of a cDNA clone encoding a putative white spruce glycine-rich RNA binding protein

A presumably full-length cDNA encoding a putative glycine-rich RNA binding protein was isolated from a lambdaZAP cDNA library prepared from mRNAs extracted from needles of 2year old white spruce seedlings, which had been either wounded or jasmonate-treated. The cDNA, designated PgRNP (Picea glauca RNP protein), presents a 468bp open reading frame encoding a 155 amino acid protein. This polypeptide possesses an RNA binding domain (RNP-CS) and a glycine-rich domain. Comparative alignment reveals extensive homologies to glycine-rich RNA binding proteins containing an RNP-CS found in other angiosperm species. Genomic hybridization experiments suggest that the PgRNP gene is part of a small multigene family with at least four members. RNA blot analysis revealed that the PgRNP transcript is expressed in all tissues from non-stressed plants. Constitutive mRNA level was found in needle tissue from control as well as methyl-jasmonate treated plants. Wounding had no clear induction effect. Jasmonic acid treatment and systemic wound response had a positive effect on transcript accumulation. Transcript accumulation was slightly induced by cold in needles, and repressed by drought stress in both needle and root tissues of 2year old plants. Finally, the level of PgRNP accumulation was induced by wounding and repressed in 2week old dark-grown seedlings upon jasmonate treatments.

Molecular cloning of a gut-specific chitinase cDNA from the beetle Phaedon cochleariae

A cDNA encoding a chitinase of Pheadon cochleariae was isolated from a larval gut library. The cDNA encodes a preenzyme with a putative 20 amino-acid signal peptide and a 385 amino-acid mature enzyme of calculated mass of 42.7 kDa. Amino-acid alignment shows 24-33% identity to other insect and crustacea chitinases. The sequence lacks C-terminus domains but active site residues are conserved. Northern analysis localizes the mRNA to guts of feeding larvae. Southern blot analysis, with a complete cDNA probe, suggests that the P. cochleariae genome may contain several chitinase genes. Activity gels show that two groups of chitinases are expressed in the insect. One group comprises chitinases of 30-40 kDa that are active at pH 5.0 and detected in guts of feeding larvae and adults, as well as in pre-pupae and pupae. The other group comprises chitinases of 40-70 kDa that are more active at pH 7.0 and are mainly expressed in pre-pupae and pupae. The biological significance of both groups of chitinases is discussed.

Overexpression of glutathione synthetase in indian mustard enhances cadmium accumulation and tolerance

An important pathway by which plants detoxify heavy metals is through sequestration with heavy-metal-binding peptides called phytochelatins or their precursor, glutathione. To identify limiting factors for heavy-metal accumulation and tolerance, and to develop transgenic plants with an increased capacity to accumulate and/or tolerate heavy metals, the Escherichia coli gshII gene encoding glutathione synthetase (GS) was overexpressed in the cytosol of Indian mustard (Brassica juncea). The transgenic GS plants accumulated significantly more Cd than the wild type: shoot Cd concentrations were up to 25% higher and total Cd accumulation per shoot was up to 3-fold higher. Moreover, the GS plants showed enhanced tolerance to Cd at both the seedling and mature-plant stages. Cd accumulation and tolerance were correlated with the gshII expression level. Cd-treated GS plants had higher concentrations of glutathione, phytochelatin, thiol, S, and Ca than wild-type plants. We conclude that in the presence of Cd, the GS enzyme is rate limiting for the biosynthesis of glutathione and phytochelatins, and that overexpression of GS offers a promising strategy for the production of plants with superior heavy-metal phytoremediation capacity.

Structural alterations of lignins in transgenic poplars with depressed cinnamyl alcohol dehydrogenase or caffeic acid O-methyltransferase activity have an opposite impact on the efficiency of industrial kraft pulping

We evaluated lignin profiles and pulping performances of 2-year-old transgenic poplar (Populus tremula x Populus alba) lines severely altered in the expression of caffeic acid/5-hydroxyferulic acid O-methyltransferase (COMT) or cinnamyl alcohol dehydrogenase (CAD). Transgenic poplars with CAD or COMT antisense constructs showed growth similar to control trees. CAD down-regulated poplars displayed a red coloration mainly in the outer xylem. A 90% lower COMT activity did not change lignin content but dramatically increased the frequency of guaiacyl units and resistant biphenyl linkages in lignin. This alteration severely lowered the efficiency of kraft pulping. The Klason lignin level of CAD-transformed poplars was slightly lower than that of the control. Whereas CAD down-regulation did not change the frequency of labile ether bonds or guaiacyl units in lignin, it increased the proportion of syringaldehyde and diarylpropane structures and, more importantly with regard to kraft pulping, of free phenolic groups in lignin. In the most depressed line, ASCAD21, a substantially higher content in free phenolic units facilitated lignin solubilization and fragmentation during kraft pulping. These results point the way to genetic modification of lignin structure to improve wood quality for the pulp industry.

Manipulation of glutathione and amino acid biosynthesis in the chloroplast

Poplars (Populus tremula x Populus alba) were transformed to overexpress Escherichia coli gamma-glutamylcysteine synthetase (gamma-ECS) or glutathione synthetase in the chloroplast. Five independent lines of each transformant strongly expressed the introduced gene and possessed markedly enhanced activity of the gene product. Glutathione (GSH) contents were unaffected by high chloroplastic glutathione synthetase activity. Enhanced chloroplastic gamma-ECS activity markedly increased gamma-glutamylcysteine and GSH levels. These effects are similar to those previously observed in poplars overexpressing these enzymes in the cytosol. Similar to cytosolic gamma-ECS overexpression, chloroplastic overexpression did not deplete foliar cysteine or methionine pools and did not lead to morphological changes. Light was required for maximal accumulation of GSH in poplars overexpressing gamma-ECS in the chloroplast. High chloroplastic, but not cytosolic, gamma-ECS activities were accompanied by increases in amino acids synthesized in the chloroplast. We conclude that (a) GSH synthesis can occur in the chloroplast and the cytosol and may be up-regulated in both compartments by increased gamma-ECS activity, (b) interactions between GSH synthesis and the pathways supplying the necessary substrates are similar in both compartments, and (c) chloroplastic up-regulation of GSH synthesis is associated with an activating effect on the synthesis of specific amino acids formed in the chloroplast.

Expression of antisense chalcone synthase RNA in transgenic hybrid walnut microcuttings. Effect on flavonoid content and rooting ability

Walnut somatic embryos (Juglans nigra x Juglans regia) were transformed with a vector containing a neomycin phosphotransferase II, a beta-glucuronidase and an antisense chalcone synthase (chs) gene. This antisense construct included a 400 bp cDNA fragment of a walnut chs gene under the control of the duplicated CaMV-35S promoter. Molecular, biochemical and biological characterizations were performed both on transformed embryos propagated by secondary somatic embryogenesis and on microshoots developed by in vitro culture of embryonic epicotyls from somatic embryos. Thirteen transformed lines with the vector containing the antisense chs gene, one line with only the gus and nptII genes and one untransformed line were maintained in tissue culture. Six of the antisense lines were shown to be flavonoid-deficient. They exhibited a strongly reduced expression of chs genes, very low chalcone synthase activity and no detectable amounts of quercitrin, myricitrin, flavane-3-ols and proanthocyanidins in stems. Rooting tests showed that decreased flavonoid content in stems of antisense chs transformed lines was associated with enhanced adventitious root formation. Free auxin and conjugated auxin contents were determined during the latter phase of the micropropagation, and no variations were detected between control and antisense chs transformed lines. The in vitro plants developed a large basal callus and apical necrosis upon auxinic induction and the transformed lines highly deficient in flavonoids were more sensitive to exogenous application of indolebutyric acid (IBA).

Two strains of cabbage seed weevil (Coleoptera: Curculionidae) exhibit differential susceptibility to a transgenic oilseed rape expressing oryzacystatin I

The aim of this study was to assess the potential effect of a transgenic line of oilseed rape expressing oryzacystatin I (OCI) on two strains of cabbage seed weevil. The level of OCI expression in seeds was approximately 0.05% of total soluble proteins. The insects were field-collected in two different locations, and their progeny was analyzed after a 3 week-development in pods. Both strains showed a similar pattern of proteolytic activity, and similar levels of OCI-sensitive proteinase activity in vitro. However, the larvae showed differential susceptibility to the transgenic plants. Despite inhibition of digestive proteinases in vitro by OCI in both strains, one strain showed an increased growth rate when fed the transgenic seeds, while the other strain remained unaffected. While suggesting the importance of studying individuals from different populations when assessing the effect of proteinase inhibitor-expressing plants on insect growth, our results also point out the necessity of studying the biochemical interactions taking place in vivo between the recombinant inhibitors and their target proteinases.

Overexpression of iron superoxide dismutase in transformed poplar modifies the regulation of photosynthesis at low CO2 partial pressures or following exposure to the prooxidant herbicide methyl viologen

Chloroplast-targeted overexpression of an Fe superoxide dismutase (SOD) from Arabidopsis thaliana resulted in substantially increased foliar SOD activities. Ascorbate peroxidase, glutathione reductase, and monodehydroascorbate reductase activities were similar in the leaves from all of the lines, but dehydroascorbate reductase activity was increased in the leaves of the FeSOD transformants relative to untransformed controls. Foliar H2O2, ascorbate, and glutathione contents were comparable in all lines of plants. Irradiance-dependent changes in net CO2 assimilation and chlorophyll a fluorescence quenching parameters were similar in all lines both in air (21% O2) and at low (1%) O2. CO2-response curves for photosynthesis showed similar net CO2-exchange characteristics in all lines. In contrast, values of photochemical quenching declined in leaves from untransformed controls at intercellular CO2 (Ci) values below 200 microL L-1 but remained constant with decreasing Ci in leaves of FeSOD transformants. When the O2 concentration was decreased from 21 to 1%, the effect of FeSOD overexpression on photochemical quenching at limiting Ci was abolished. At high light (1000 micromol m-2 s-1) a progressive decrease in the ratio of variable (Fv) to maximal (Fm) fluorescence was observed with decreasing temperature. At 6(o)C the high-light-induced decrease in the Fv/Fm ratio was partially prevented by low O2 but values were comparable in all lines. Methyl viologen caused decreased Fv/Fm ratios, but this was less marked in the FeSOD transformants than in the untransformed controls. These observations suggest that the rate of superoxide dismutation limits flux through the Mehler-peroxidase cycle in certain conditions.

High level of resistance to proteinase inhibitors may be conferred by proteolytic cleavage in beetle larvae

Incorporation of genes encoding proteinase inhibitors into oilseed rape genome could confer resistance to Coleoptera, which are the major pests on rape in Europe. A detailed study of the digestive proteinase of a model cruciferous-feeding Coleoptera, Phaedon cochleariae, showed that this insect relies on a complex proteolytic system including serine, cysteine, aspartyl proteinases, and leucine aminopeptidases. The inhibition of general and specific activities by a range of proteinase inhibitors in vitro suggested that oryzacystatin I (OCI) and Bowman-Birk inhibitor (BBI) would have adverse effects when ingested by the larvae. However, the growth and the feeding of larvae reared on oilseed rape leaf discs treated with a high dose of OCI and/or BBI were not affected. Moreover, the levels and patterns of proteolytic activities were not modified in these larvae. The study of the interactions between P. cochleariae larval proteinases and OCI and BBI revealed that both inhibitors were rapidly cleaved by serine proteinases in association with leucine aminopeptidases, and consequently lost their inhibitory capacity. This mechanism of resistance is very efficient, and may be widespread among Coleoptera. The major implications for insect control using proteinase inhibitor-based strategies are discussed.

Growth stimulation of beetle larvae reared on a transgenic oilseed rape expressing a cysteine proteinase inhibitor

The resistance of a transgenic line of oilseed rape expressing constitutively the cysteine proteinase inhibitor oryzacystatin I (OCI) was assessed against Psylliodes chrysocephala L. (Coleoptera: Chrysomelidae). The levels of OCI expression in the transformed line averaged 0.2% and 0.05% of total soluble protein in leaves and petioles respectively. In vitro analyses showed that P. chrysocephala larvae use both cysteine and serine proteinases for protein digestion, and that all the cysteine proteolytic activity is OCI-sensitive. However, bioassays showed that adults fed identically on leaf discs from control or transformed plants. When larvae were reared on transgenic plants expressing OCI, they showed an increase in weight gain compared to those reared on control plants. Furthermore, those larvae from transgenic plants exhibited a 2-fold increase in both cysteine and serine proteolytic activity as a reponse to the presence of OCI. The plasticity of insect digestive physiology and feeding behaviour are discussed, as well as the relevance of engineering a genotype expressing both types of proteinase inhibitors.

Agrobacterium tumefaciens-mediated transformation of hybrid larch (Larix kaempferi T L. decidua) and transgenic plant regenerationn

A transformation procedure was developed for hybrid larch embryogenic tissue using Agrobacterium tumefaciens. The cocultivation procedure yielded one to two transformation events per 100 cocultivated masses. The addition of 100 µM coniferyl alcohol increased the yield. This improved procedure was successfully applied to three other genotypes. After 3 months on selective medium, the transgenic tissue remained embryogenic, which allowed production of transgenic plants in the greenhouse. Stable integration of the transgene was confirmed by PCR and Southern hybridisation on transformed tissues and acclimatised plants.

Modification of thiol contents in poplars (Populus tremula x P. alba) overexpressing enzymes involved in glutathione synthesis

The hybrid poplar (Populus tremula x P. alba) was transformed to express the Escherichia coli gene for gamma-glutamylcysteine synthetase (EC 6.3.2.2: gamma-ECS) in the cytosol. Four transformed lines of poplar were obtained. These were phenotypically indistinguishable from untransformed poplars. Three lines, ggs28 (Noctor et al. 1996, Plant Physiol 112: 1071-1078), ggs11 and ggs5 possessed high levels of bacterial gene transcripts. Line ggs17 had lower transcript levels. Antisera were prepared against bacterial gamma-ECS and bacterial glutathione synthetase (EC 6.3.2.3: GS). Using the antiserum prepared against the purified His-tagged E. coli gamma-ECS, lines ggs28, ggs11 and ggs5 were shown to possess abundant quantities of the bacterial protein, whereas ggs17 contained lower amounts. The antiserum prepared against the purified His-tagged E. coli GS was also effective in screening poplars transformed with the E. coli gene coding for this enzyme. Immunoblots of leaf extracts from poplars overexpressing GS using this antibody revealed two bands. The extractable foliar gamma-ECS activities of the gamma-ECS transformants were in quantitative agreement with the protein levels. Lines ggs28, ggs11 and ggs5 had approximately 30-fold higher gamma-ECS activity than untransformed poplars, whereas in ggs17 this activity was only augmented about 3-fold. The lines strongly overexpressing gamma-ECS, ggs28, ggs11 and ggs5, contained enhanced foliar levels of cysteine (up to 2-fold), gamma-glutamylcysteine (5- to 20-fold) and glutathione (2- to 4-fold). Foliar thiol contents in ggs17 were no different to those of untransformed plants.

Red Xylem and Higher Lignin Extractability by Down-Regulating a Cinnamyl Alcohol Dehydrogenase in Poplar

Cinnamyl alcohol dehydrogenase (CAD) catalyzes the last step in the biosynthesis of the lignin precursors, the monolignols. We have down-regulated CAD in transgenic poplar (Populus tremula X Populus alba) by both antisense and co-suppression strategies. Several antisense and sense CAD transgenic poplars had an approximately 70% reduced CAD activity that was associated with a red coloration of the xylem tissue. Neither the lignin amount nor the lignin monomeric composition (syringyl/guaiacyl) were significantly modified. However, phloroglucinol-HCl staining was different in the down-regulated CAD plants, suggesting changes in the number of aldehyde units in the lignin. Furthermore, the reactivity of the cell wall toward alkali treatment was altered: a lower amount of lignin was found in the insoluble, saponified residue and more lignin could be precipitated from the soluble alkali fraction. Moreover, large amounts of phenolic compounds, vanillin and especially syringaldehyde, were detected in the soluble alkali fraction of the CAD down-regulated poplars. Alkaline pulping experiments on 3-month-old trees showed a reduction of the kappa number without affecting the degree of cellulose degradation. These results indicate that reducing the CAD activity in trees might be a valuable strategy to optimize certain processes of the wood industry, especially those of the pulp and paper industry.

Synthesis of Glutathione in Leaves of Transgenic Poplar Overexpressing [gamma]-Glutamylcysteine Synthetase

Internode stem fragments of the poplar hybrid Populus tremula x Populus alba were transformed with a bacterial gene (gshl) for [gamma]-glutamylcysteine synthetase ([gamma]-ECS) targeted to the cytosol. Lines overexpressing [gamma]-ECS were identified by northern analysis, and the transformant with the highest enzyme activity was used to investigate the control of glutathione synthesis. Whereas foliar [gamma]-ECS activity was below the limit of detection in untransformed plants, activities of up to 8.7 nmol mg-1 protein min-1 were found in the transformant, in which the foliar contents of [gamma]-glutamylcysteine ([gamma]-EC) and glutathione were increased approximately 10- and 3-fold, respectively, without affecting either the reduction state of the glutathione pool or the foliar cysteine content. A supply of exogenous cysteine to leaf discs increased the glutathione content from both transformed and untransformed poplars, and caused the [gamma]-EC content of the transformant discs to increase still further. The following conclusions are drawn: (a) the native [gamma]-ECS of untransformed poplars exists in quantities that are limiting for foliar glutathione synthesis; (b) foliar glutathione synthesis in untransformed poplars is limited by cysteine availability; (c) in the transformant interactions between glutathione synthesis and cysteine synthesis operate to sustain the increased formation of [gamma]-EC and glutathione; and (d) the foliar glutathione content of the transformant is restricted by cysteine availability and by the activity of glutathione synthetase.

Identification of stable plant cystatin/nematode proteinase complexes using mildly denaturing gelatin/polyacrylamide gel electrophoresis

The biochemical interactions between two cystatins from rice seeds, oryzacystatin I (OCI) and oryzacystatin II (OCII), and the cysteine proteinases from three plant parasitic nematodes, Meloidogyne hapla, M. incognita and M. javanica, were assessed using standard protease assays and mildly denaturing gelatin/polyacrylamide gel electrophoresis (gelatin/PAGE). Activity detected in extracts of preparasitic second-stage larvae (J2) from M. hapla was optimal at pH 5.5 and was inhibited in vitro by the cysteine proteinase inhibitors trans-epoxysuccinyl-L-leucylamido-(4-guanidino) butane, hen egg cystatin, OCI, and OCII. As demonstrated by class-specific activity staining, all the activity measured between pH 3.5 and pH 7.5 was accounted for by a major proteinase form, Mhp1, and two minor forms, Mhp2 and Mhp3. Mhps were also detected in extracts and excretions of parasitic J2 and adult females, indicating their continuous expression throughout development of M. hapla, and their possible involvement in the extracellular degradation of proteins. Interestingly, the two plant cysteine proteinase inhibitors OCI and OCII showed different degrees of affinity for the major proteinase form, Mhp1. Both inhibitors almost completely inactivated this proteinase in native conditions but, unlike OCII, OCI conserved a high affinity for Mhp1 during mildly denaturing gelatin/PAGE, showing the differential stabilities of the OCI/Mhp1 and OCII/Mhp1 complexes. In contrast to Mhp1, the major cysteine proteinases detected in the two closely related species M. incognita and M. javanica were strongly inhibited by OCII, while the inhibition of OCI was partly prevented during electrophoresis. This species-related efficiency of plant cystatins against nematode cysteine proteinases could have practical implications when planning their use to control nematodes of the genus Meloidogyne.

Overexpression of glutathione reductase but not glutathione synthetase leads to increases in antioxidant capacity and resistance to photoinhibition in poplar trees

A poplar hybrid, Populus tremula x Populus alba, was transformed with the bacterial genes for either glutathione reductase (GR) (gor) or glutathione synthetase (GS) (gshII). When the gor gene was targeted to the chloroplasts, leaf GR activities were up to 1000 times greater than in all other lines. In contrast, targeting to the cytosol resulted in 2 to 10 times the GR activity. GR mRNA, protein, and activity levels suggest that bacterial GR is more stable in the chloroplast. When the gshII gene was expressed in the cytosol, GS activities were up to 100 times greater than in other lines. Overexpression of GR or GS in the cytosol had no effect on glutathione levels, but chloroplastic-GR expression caused a doubling of leaf glutathione and an increase in reduction state. The high-chloroplastic-GR expressors showed increased resistance to photoinhibition. The herbicide methyl viologen inhibited CO2 assimilation in all lines, but the increased leaf levels of glutathione and ascorbate in the high-chloroplastic-GR expressors persisted despite this treatment. These results suggest that overexpression of GR in the chloroplast increases the antioxidant capacity of the leaves and that this improves the capacity to withstand oxidative stress.

Expression of Agrobacterium rhizogenes auxin biosynthesis genes in transgenic tobacco plants

Plant oncogenes aux1 and aux2 carried by the TR-DNA of Agrobacterium rhizogenes strain A4 encode two enzymes involved in the auxin biosynthesis pathway in transformed plant cells. The short divergent promoter region between the two aux-coding sequences contains the main regulatory elements. This region was fused to the uidA reporter gene and introduced into Nicotiana tabacum in order to investigate the regulation and the tissue specificity of these genes. Neither wound nor hormone induction could be detected on transgenic leaf discs. However, phytohormone concentration and auxin/cytokinin balance controlled the expression of the chimaeric genes in transgenic protoplasts. The expression was localised in apical meristems, root tip meristems, lateral root primordia, in cells derived from transgenic protoplasts and in transgenic calli. Histological analysis showed that the expression was located in cells reactivated by in vitro culture. Experiments using cell-cycle inhibitors such as hydroxyurea or aphidicolin on transgenic protoplast cultures highly decreased the beta-glucuronidase activity of the chimaeric genes. These results as well as the histological approach suggest a correlation between expression of the aux1 and aux2 genes and cell division.

Oncogene arrangement in a shooty strain of Agrobacterium tumefaciens

The Agrobacterium tumefaciens nopaline strain 82.139 induces non-teratogenic shooty tumours on several plant species. We have determined the position of the T-region oncogenes in a 11.4 kb Xba I fragment which shows a general organization similar to its pTiC58 counterpart. Sequence analysis of the 4.7 kb right part of this fragment allowed us to identify the pTi82.139 ipt, 6b and nos coding sequences. pTi82.139 lacks the 6a gene, which lies between the ipt and 6b genes in pTiC58. The intervening region between the 6b and the nos genes contains an additional ORF with homology to ORF 21 (transcript 3') from the TR-DNA of octopine strain pTi15955.

A reporter gene under the control of tms or aux promoters is differentially expressed in tobacco and barley protoplasts

Agrobacterium tumefaciens and some Agrobacterium rhizogenes strains possess auxin biosynthesis genes (tms and aux genes respectively), responsible for a de novo auxin biosynthetic pathway in transformed plant cells. A comparison is presented of the potential expression of these genes in a monocotyledonous (barley) and a dicotyledonous plant (tobacco). The promoters of the genes were translationally fused to the β-glucuronidase reporter gene and analysed in transient expression experiments. The tms and aux fusions were highly expressed in tobacco, but not in barley. However, the aux enhancer active in tobacco, conferred low β-glucuronidase expression in barley when fused to a truncated cauliflower mosaic virus 35S promoter. The results are discussed in relation to the differential responses to Agrobacterium infection in monocots and dicots.

Enhancement of the endogenous cytokinin concentration in poplar by transformation with Agrobacterium T-DNA gene ipt

The agrobacterial isopentenyltransferase (ipt) gene, under the control of its native promoter, was transferred to poplar (Populus tremula x P. alba) by an Agrobacterium co-cultivation method. The ipt-transformed stem explants developed calli that regenerated many buds in the absence of exogenous cytokinins. Microcuttings of the ipt transformants exhibited frequently branching shoots with short internodes that were unable to root. In this material, the concentrations of zeatin, zeatin riboside and isopentenyladenosine, determined by an indirect enzyme-linked immunosorbent assay (ELISA), were 4.8-. 17.1- and 14.6-fold higher, respectively, than in non-transformed shoots. Results are discussed with regard to cytokinin metabolism.

Multiple regions of a divergent promoter control the expression of the Agrobacterium rhizogenes aux1 and aux2 plant oncogenes

The two auxin biosynthesis genes, aux1 and aux2 of Agrobacterium rhizogenes strain A4, are located on opposite DNA strands with a short integenic region (394 bp) between their coding sequences. A functional analysis of this divergent promoter is presented. The transcription initiation sites of the two aux genes were determined and regions important for promoter activity were identified by deletion and transient expression analyses in tobacco protoplasts. The promoter activity of the aux intergenic region was demonstrated. A strong enhancer element contained within an 84 bp promoter fragment was identified. Far upstream regions were shown to have negative effects on the promoter activity of the short intergenic region. Interactions between positive elements in the intergenic region and negative effects of the upstream sequences may be the basis of strict control of the auxin biosynthesis necessary for the induction and maintenance of hairy root growth.

Transformation of rapid cycling cabbage (Brassica oleracea var. capitata) with Agrobacterium rhizogenes

Genetically transformed cabbage (Brassica oleracea var. capitata) roots were obtained after inoculation with two engineered Agrobacterium rhizogenes strains, each harbouring a plant selectable marker gene in their T-DNA. Axenic root clones resistant to kanamycin or hygromycin B were established, most of which did not exhibit the phenotypic characteristics of Ri-transformed roots. Shoot regeneration was induced from roots after treatment with 2,4-dichlorophenoxyacetic acid (2,4-D). The resulting plants exhibited various phenotypes: some looked normal, while others showed the transformed phenotype observed in other species. Direct evidence for genetic transformation was obtained by molecular hybridization. The trait was transmitted to the progeny. Transformed cabbage plants can be obtained within 6 months using this approach.

Transgenic poplars: expression of chimeric genes using four different constructs

Leaf or stem explants of a hybrid poplar clone (Populus tremula X Populus alba), sensitive to Agrobacterium tumefaciens, were co-cultivated either by an octopine or a nopaline disarmed A. tumefaciens modified strain. Transformed poplar shoots were readily regenerated from explants. The protocol was improved using the nopaline disarmed strain C58/pMP90 with the binary vector pBI121. This protocol was then used to test three other vectors. The first one, possessing a nptII gene fused to the CaMV 19S promoter, permitted regeneration of transformed shoots in presence of 50 to 100 mg/l kanamycin. The two other vectors carried an additional nptII gene under the control of the CaMV 35S or CaMV 35S promoter with a double enhancer sequence (CaMV 70). CaMV 70 promoter provided consistently higher level of gene expression than the other promoters in both callus and leaf tissues.

The TR-DNA region carrying the auxin synthesis genes of the Agrobacterium rhizogenes agropine-type plasmid pRiA4: nucleotide sequence analysis and introduction into tobacco plants

We have determined the nucleotide sequence of a 6-kilobase fragment of the Agrobacterium rhizogenes plasmid pRiA4 TR-region that carries genes (aux1 and aux2) responsible for auxin biosynthesis in transformed plant cells. Sequence analysis revealed two open reading frames corresponding to proteins of 749 amino acids for the aux1 gene and 466 amino acids for the aux2 gene. We observed significant similarity between the amino acid sequences deduced from the pRiA4 aux genes and those of the auxin biosynthesis genes of A. tumefaciens octopine-type Ti plasmids, the iaaM and iaaH genes of Pseudomonas savastanoi, and different genes of the pRiA4 TL-region; however, the 5'-flanking regions of the pRi and pTi auxin biosynthesis genes were found to be completely different. Transgenic tobacco plants containing this entire 6-kilobase fragment of the pRiA4 TR-region have been obtained. Regenerated plants are phenotypically normal. The aux1 gene is not or is very weakly expressed in these plants, but expression of the aux2 gene leads to a modified root phenotype when plants are grown on medium containing an auxin precursor (naphthalene acetamide).

Analysis of TR-DNA/plant junctions in the genome of a Convolvulus arvensis clone transformed by Agrobacterium rhizogenes strain A4

A Charon 4A phage library, containing insert DNA isolated from a morning glory (Convolvulus arvensis) plant genetically transformed by Ri T-DNA from Agrobacterium rhizogenes strain A4, was used to isolate a lambda clone that contains part of the Ri TL-DNA and the complete TR-DNA. The two Ri T-DNAs were recovered adjacent to each other in a tail-to-tail configuration (i.e. with the TR-DNA inverted with respect to the TL-DNA). Comparison of nucleotide sequences from this lambda clone with the corresponding sequences from the Ri plasmid allowed us to determine the location of the T-DNA/plant junction for the right end of the TL-DNA and the left and right ends of the TR-DNA. We located, near each of these borders, a 24 bp sequence that is similar to the 24 bp consensus sequence found near the pTi T-DNA extremities. In addition, sequences similar to the "core" overdrive sequence from pTi are located near each right border. Hybridization and nucleotide sequence analysis of the DNA adjacent to the TL/TR junction shows that no plant DNA is located between the TL and TR-DNAs and suggests that the plant DNA adjacent to the end of the TR-DNA may have been rearranged during the integration into the plant genome.

Expression vectors based on the Agrobacterium rhizogenes Ri plasmid transformation system

This article describes several new expression vectors that capitalize on the ability of Agrobacterium rhizogenes to transfer DNA from its Ri plasmid to the plant nuclear genome. The intermediate vectors described include an expression cassette based on one of the three following promoters: the nopaline synthase promoter, or the cauliflower mosaic virus (CaMV) promoters responsible for transcription of either the 19S or 35S CaMV RNA. The termination and polyadenylation signals are either from the nopaline synthase gene or from CaMV. The expression micro-Ri plasmid described bears a selectable marker gene and an expression cassette cloned between the borders of the TL-region of the Ri plasmid of A. rhizogenes A4. Different strategies for using these vectors to introduce chimeric genes into plants are described, and the advantages and disadvantages of the two types of vectors are discussed.