Transcriptomics of tomato plants infected with TYLCSV or expressing the central TYLCSV Rep protein domain uncover changes impacting pathogen response and senescence

To establish a successful infection viruses need to overcome plant innate immune responses and redirect host gene expression for their multiplication and diffusion. Tomato yellow leaf curl Sardinia virus (TYLCSV) is a geminivirus, which causes significant economic losses in tomato. The multifunctional replication associated geminivirus protein (Rep) has an important role during viral infection. In particular, the Rep central domain spanning from aa 120 to 180 is known to interact with viral and host factors. In this study, we used long serial analysis of gene expression to analyse the transcriptional profiles of transgenic tomato plants expressing the first 210 amino acids of TYLCSV Rep (Rep210) and TYLCSV-infected wild-type tomato plants (Wt-Ty). Also, we compared these profiles with those of transgenic Rep130 tomatoes. Comparison of Wt-Ty and Rep210 libraries with the wild-type one identified 118 and 203 differentially expressed genes (DEGs), respectively. Importantly, 55% of Wt-Ty DEGs were in common with Rep210, and no ones showed opposite expression. Conversely, a negligible overlap was found between Rep130 DEGs and Wt-Ty and Rep210 ones. TYLCSV- and Rep210-repressed genes, but not induced ones, overlapped with the leaf senescence process. Interestingly, TYLCSV upregulates expression of genes involved in the negative regulation of programmed cell death (PCD), several of which were also regulated by the abscisic acid. Rep210 upregulated genes related to defence response, immune system processes and negative regulation of PCD. Collectively, our results support a model in which the Rep central domain has a pivotal role in redirecting host plant gene expression.

Mutants of plant genes for developing cancer vaccines

Preventive Human Papillomavirus (HPV) vaccination is an expensive practice and it may be an insufficient tool to tackle cervical cancer worldwide. Therapeutic intervention is seeking for safe/effective vaccines inducing the activation of CD8+ cytotoxic T lymphocytes (CTLs) that is required to clear the tumor. Linking a tumor-specific antigen (i.e. the E7 oncoprotein of the 'high risk' HPVs) to molecules able to increase its immune 'visibility' represents a strategy to force the immune system to fight cancer. We focused on plants as sources of innovative immunostimulatory sequences. We have already shown the anti-cancer activity obtained by fusing E7GGG (a mutagenized E7 gene from the high risk HPV type 16) to the coat protein of a plant virus, the Potato Virus X. We are now investigating plant-derived carriers, such as the 'Ribosome inactivating proteins' (RIPs), so far used to develop immunotoxins for targeted cancer therapy. Beside toxicity, RIPs have other features (i.e. immunogenicity, ability to modulate immune functions and apoptosis induction) that could be useful tools to use in tumor immunotherapy. A non toxic mutant of saporin (SAP-KQ) was used as a carrier for the E7GGG gene in the context of a DNA-based vaccine. We show here that fusion constructs of SAP-KQ with E7GGG can induce E7-specific Immunoglobulins (IgGs), CTLs and Delayed-Type Hypersensitivity (DTH) affecting the growth of E7-expressing tumors in mice. These data demonstrate that mutant plant genes hold promise to improve the poor immunogenicity of tumor-associated cancer antigens and could contribute to the evolution of new cancer immunotherapy.

Signal peptide-regulated toxicity of a plant ribosome-inactivating protein during cell stress

The fate of the type I ribosome-inactivating protein (RIP) saporin when initially targeted to the endoplasmic reticulum (ER) in tobacco protoplasts has been examined. We find that saporin expression causes a marked decrease in protein synthesis, indicating that a fraction of the toxin reaches the cytosol and inactivates tobacco ribosomes. We determined that saporin is largely secreted but some is retained intracellularly, most likely in a vacuolar compartment, thus behaving very differently from the prototype RIP ricin A chain. We also find that the signal peptide can interfere with the catalytic activity of saporin when the protein fails to be targeted to the ER membrane, and that saporin toxicity undergoes signal sequence-specific regulation when the host cell is subjected to ER stress. Replacement of the saporin signal peptide with that of the ER chaperone BiP reduces saporin toxicity and makes it independent of cell stress. We propose that this stress-induced toxicity may have a role in pathogen defence.

Differential expression of saporin genes upon wounding, ABA treatment and leaf development

Saporins are type 1 ribosome-inactivating proteins (RIPs: EC 3.2.2.22) produced in various organs of Saponaria officinalis L. Two distinct saporin types, saporin-L and saporin-S isoforms, were respectively purified from the intra- and extra-cellular fractions of soapwort leaves. The saporin-L isoform was lowly identical, differed for toxicity, molecular mass and amino acid composition from saporin-S proteins forming a new monophyletic group. Genes encoding both L- and S-type isoforms were cloned from leaf-specific cDNA library; the encoded products included the N-terminal diversity observed by protein sequencing and showed compatible weights with those from mass spectra. These genes were intron-less belonging to small gene families. Reverse transcription polymerase chain reaction/quantitative reverse transcription polymerase chain reaction experiments evidenced their differential expression during leaf development, wounding and abscisic acid treatment. These results suggest that the saporin-L and -S proteins may play diversified roles during stress responses.

Hydration, sporoderm breaking and germination of Cupressus arizonica pollen

In vitro and in vivo rehydration and germination in Cupressus arizonica pollen were examined using light and scanning electron microscopy. Shed pollen has 12.6% water content, which reduced to 8.2% after dispersal, and this latter pollen survived for some months at room temperature and for years at -10 degrees C. Rehydration requires breaking of the sporoderm walls and depends on the composition and pH of the rehydration medium. Acidity restrains the breakage, while alkalinity promotes it. Pollen division follows exine shedding and requires the persistence of the mucilaginous layer; hence, pH values countering these outcomes prevent division. Division results in a large and a small cell separated by a callosic wall. A pollen tube develops from the innermost intine of the large cell, which is callosic, and extends into the mucilaginous middle intine. The percentage germination never exceeded 17% in all tested media. In vivo, pollen rehydrates and casts off the exine in the micropylar drop. Drop withdrawal brings pollen to the apical nucellar cells that degenerate in the meantime, and it leaves a deposit on the surface of the micropylar canal. After contaction of the nucellar cells, the pollen flattens and its mucilaginous layer shrinks and disappears. This occurs simultaneously with sealing of the micropylar canal. During this time, pollen divides asymmetrically without the callosic wall, and the larger cell develops a tube in the interface with the nucellus. Only some pollen grains accomplish adhesion to the nucellus and germinate. The in vitro and in vivo developmental stages are discussed.

High doses of atrazine do not disrupt activity and expression of aromatase in female gonads of juvenile goldfish (Carassius auratus L.)

Juveniles female goldfish were exposed to atrazine (2-chloro-4-ethylamino-6-isopropylamino-s-triazine) at high doses, 100 and 1000 microg l(-1) during 56 days in order to evaluate the potential action of the herbicide as an endocrine disruptor. Plasma concentration of estradiol (E2) and 11-ketotestosterone (11-KT) as well as activity and expression of aromatase in the gonads were evaluated. These parameters were completed with morphological measures such as gonadosomatic index (GSI) and histological analyses of gonads. Morphological parameters at both 100 and 1000 microg l(-1) did not show any significant differences with the control groups. Correlated to the pathway hypothesized, no time-, dose-related effects were detected on the aromatase activity and the expression in the gonads of juvenile female goldfish. The same conclusion was attributed regarding the circulating E2 where no perceptible variation was detected. Nevertheless, a hormonal imbalance was detected for plasma concentration of the sex steroid 11-KT of fish exposed to 1000 microg l(-1) after 56 days exposure. In these particular experimental conditions, we failed to demonstrate an effect of atrazine through the induction of aromatase and hormonal imbalance associated.

Peach [Prunus persica (L.) Batsch] KNOPE1, a class 1 KNOX orthologue to Arabidopsis BREVIPEDICELLUS/KNAT1, is misexpressed during hyperplasia of leaf curl disease

Class 1 KNOTTED-like (KNOX) transcription factors control cell meristematic identity. An investigation was carried out to determine whether they maintain this function in peach plants and might act in leaf curliness caused by the ascomycete Taphrina deformans. KNOPE1 function was assessed by overexpression in Arabidopsis and by yeast two-hybrid assays with Arabidopsis BELL proteins. Subsequently, KNOPE1 mRNA and zeatin localization was monitored during leaf curl disease. KNOPE1 and Arabidopsis BREVIPEDICELLUS (BP) proteins fell into the same phyletic group and recognized the same BELL factors. 35S:KNOPE1 Arabidopsis lines exhibited altered traits resembling those of BP-overexpressing lines. In peach shoot apical meristem, KNOPE1 was expressed in the peripheral and central zones but not in leaf primordia, identically to the BP expression pattern. These results strongly suggest that KNOPE1 must be down-regulated for leaf initiation and that it can control cell meristem identity equally as well as all class 1 KNOX genes. Leaves attacked by T. deformans share histological alterations with class 1 KNOX-overexpressing leaves, including cell proliferation and loss of cell differentiation. Both KNOPE1 and a cytokinin synthesis ISOPENTENYLTRANSFERASE gene were found to be up-regulated in infected curled leaves. At early disease stages, KNOPE1 was uniquely triggered in the palisade cells interacting with subepidermal mycelium, while zeatin vascular localization was unaltered compared with healthy leaves. Subsequently, when mycelium colonization and asci development occurred, both KNOPE1 and zeatin signals were scattered in sectors of cell disorders. These results suggest that KNOPE1 misexpression and de novo zeatin synthesis of host origin might participate in hyperplasia of leaf curl disease.

Microradiography as a tool to detect heavy metal uptake in plants for phytoremediation applications

In this paper, an application of contact microradiography with soft X-rays for detecting the uptake site of heavy metal in the whole plant leaves is investigated. The X-ray source is a laser-plasma one based on an Nd:glass laser. The soft X-ray radiation emitted from the plasma laser targets of magnesium, iron, and copper can be strongly absorbed in the leaves' regions rich in iron, magnesium, and copper. This absorbance could point to structures in the leaves where these heavy elements are found. In this work, leaves treated with copper sulfate diluted in water at 1, 2, and 5% were imaged by using a copper target, in order to evaluate differences with untreated control leaves. Our results showed that this methodology highlighted the presence of copper in the treated leaves. This new methodology should detect heavy element pollutants inside plants and it should also be a useful analytic tool in phytoremediation studies.

Expression and characterisation in E. coli of mutant forms of saporin

In the present communication, we report on the expression and characterisation in Escherichia coli of mutant derivatives of saporin, a type 1 ribosome-inactivating protein from Saponaria officinalis L. The effects of substitution of Glu 176 with Lys and those of deletion of 19 amino acids at the C-terminal were evaluated both in vivo, testing the influence of expressed proteins on bacterial growth and in vitro measuring their N-glycosidase and supercoiled DNA relaxation activities. Results indicate that both modifications of the wild-type protein abolish its toxicity to bacterial cells and impair its enzymatic activity on polynucleotide substrates, either RNA or DNA.

Interactions between saporin, a ribosome-inactivating protein, and DNA: a study by atomic force microscopy

Saporins are enzymes belonging to the PNAG class (polynucleotide: adenosine glycosidase), plant enzymes commonly known as ribosome-inactivating proteins (RIP), as a result of their property of irreversibly damaging eukaryotic ribosomes. Direct imaging with tapping-mode atomic force microscopy (AFM) has been used to study pGEM-4Z plasmid DNA binding to the saporin-SO6 (isoform from Saponaria officinalis seeds). Saporin wrapped the plasmidic DNA, and distribution of the enzyme molecules along the DNA chain was markedly variable; plasmid digested with saporin-SO6 appeared fragmented or topologically modified. The supercoiled DNA strands were cleaved, giving rise to a linearized form and to relaxed forms. Electrophoretic analysis of the effect of standard preparations of saporin-SO6 on pGEM-4S confirmed the presence of DNA strand-cleaving activity.

Effects of atrazine on sex steroid dynamics, plasma vitellogenin concentration and gonad development in adult goldfish (Carassius auratus)

Sexually mature goldfish (Carassius auratus) of both sexes were exposed to two doses (100 and 1000 microg/l) of the widely used herbicide atrazine (2-chloro-4-ethylamino-6-isopropylamino-s-triazine) for a period of 21 days and effects on the concentrations of gonad and plasma sex steroids (testosterone (T), 17beta-estradiol (E2) and 11-ketotestosterone (11-KT)), plasma vitellogenin (VTG) and gonad histo-morphology assessed. Atrazine did not show any obvious estrogenic effect in males, as determined by a lack of vitellogenin induction. There were, however, effects of atrazine on plasma androgen concentrations (androgen dynamics) and tissue (plasma and gonad) estrogen concentrations in male goldfish; exposure to 1000 microg/l atrazine induced suppression in both testosterone and 11-ketotestosterone, and resulted in elevated 17beta-estradiol, after 21 day of exposure. Further, these suppressive effects on plasma androgens and the induction in estrogen were dose- and time-related. The highest atrazine exposure dose induced structural disruption in the testis and both 100 and 1000 microg/l induced elevated levels of atresia in ovaries.

Monitoring urban air particulate matter (fractions PM 2.5 and PM 10) genotoxicity by plant systems and human cells in vitro: a comparative analysis

Increased incidence of mortality and sickness due to cardiopulmonary complications has been associated with elevated levels of urban air particles (UAP), with an aerodynamic diameter of 10 microm (PM 10) and 2.5 microm (PM 2.5). In the present report alternative plant systems and human cells in vitro are associated with human hazard and genotoxic risk assessment of UAP. The genotoxic activities associated with the coarse (PM 10) and the fine fraction (PM 2.5) of airborne particulates have been analyzed by evaluating micronuclei induction and/or sister-chromatid exchange (SCE) using in vitro models of Daucus carota and HS 27 human fibroblast cell suspensions and Zea mays root meristems. Results show variability in the response of the test systems and indicate that the mutagenicity trend in both plant and human cell cultures was directly correlated to the concentration of carbon-rich particles in the fraction of the PM 2.5 airborne particulates. Moreover, in plant tissues, the frequency of micronuclei and SCE was related to an enhancement of the specific activity of the stress-related enzyme peroxidase.

Effects of atrazine on osmoregulation in the Chinese mitten crab, Eriocheir sinensis

This study integrates results from acute contamination with atrazine of isolated perfused gills, and from in vivo chronic contamination of euryhaline Chinese mitten crabs, Eriocheir sinensis, acclimated to freshwater. Atrazine 1 mg/l in contact with the basolateral membrane (IN) increases the transepithelial potential difference (TEP) from -20.8 +/- 4.9 to -29.7 +/- 3.8 mV in isolated perfused posterior gills (P < 0.01). This effect is only partially explained by a modification of Na(+) and Cl(-) active influxes. No TEP modification is detected when atrazine is added (OUT) indicating that molecular mechanisms located on the basolateral membrane are likely to be the only ones affected. Another explanation would be that cuticular barrier prevents atrazine penetration into the gill. Haemolymph osmolarity, Na(+) and Cl(-) concentrations of crabs living in freshwater contaminated with atrazine 1 mg/l during 14 days are not significantly modified. We conclude that although atrazine can disturb osmoregulatory mechanisms of isolated gills, this pollutant would be of minor importance in affecting osmoregulatory capacities of the Chinese mitten crab in natural conditions.

Antiproliferative effect and apoptotic response in vitro of human melanoma cells to liposomes containing the ribosome-inactivating protein luffin

The present study describes the liposome-mediated delivery of the type 1 ribosome-inactivating protein luffin to human melanoma cells in vitro. Luffin from Luffa cylindrica seeds has been successfully incorporated into lecithin/cholesterol and lecithin/cholesterol/dicetylphosphate negatively charged liposomes. The exposure of melanoma cells to the two types of liposomes resulted in the inhibition of protein synthesis and cell growth; apoptotic cell death was verified by means of TUNEL reaction and quantitation of cytosolic oligonucleosome-bound DNA. The toxicity of encapsulated luffin varied with the lipid composition of the vesicles; the strongest effect was observed with lecithin/cholesterol liposomes. These results identify liposome-incorporated luffin as a possible alternative to immunotoxins for the treatment of human melanoma in situ.

The plant ribosome inactivating protein saporin induces micronucleus formation in peripheral human lymphocytes in vitro

Saporin belongs to the family of plant enzymes known as ribosome inactivating proteins (RIPs) for their property to depurinate the major rRNA, thus leading to inactivation of ribosomes. In this work we analyzed the genotoxic effects of saporin, purified from root cultures of Saponaria officinalis, by evaluating micronucleus formation and by the quantitative determination of cytosolic histone-associated DNA fragments. Saporin induces micronuclei formation in cultured human lymphocytes in a dose dependent manner; treated lymphocytes show a decrease in cell viability and a concomitant increase in the apoptotic response evidenced by the appearance of cytosolic oligonucleosomes. On the other hand saporin treatment failed to induce sister-chromatid exchange (SCE) at any of the doses tested.

Differential response of human melanoma and Ehrlich ascites cells in vitro to the ribosome-inactivating protein luffin

The cytotoxicity and inhibitory effect on proliferation of the type 1 ribosome-inactivating protein luffin purified from the seeds of Luffa aegyptiaca were investigated both in human metastatic melanoma cells and in murine Ehrlich ascites tumour cells. Results indicate that luffin from the seeds of Luffa aegyptiaca is cytotoxic to the cell lines tested, with approximately 10 times greater potency in Ehrlich cells. Luffin was found to induce an increase in cytosolic oligonucleosome-bound DNA in both melanoma and Ehrlich ascites tumour cells, the level of DNA fragmentation in the former cell line being higher than in the latter. Experiments with melanoma cells indicate that an increase in cytosolic nucleosomes could be supportive of apoptosis as the type of cell death induced by luffin.

Saporin production from in vitro cultures of the soapwort Saponaria officinalis L

We report here the successful establishment of callus, cell and root cultures from explants of in-vitro-grown plantlets of the soapwort Saponaria officinalis L. The production of saporin in the different tissue systems was evaluated by determining the capability of crude extracts to inactivate protein synthesis and by Western blotting analysis. Protein synthesis inhibition varied in callus and derived cell suspensions and in cultured roots, the latter, in particular, showing the lowest specific activity. The ribosome-inactivating principle from root cultures was purified to homogeneity by cation exchange chromatography.

RolB expression pattern in the early stages of carrot somatic embryogenesis

The pattern of expression of the rolB gene, derived from the T-DNA of the plant pathogen Agrobacterium rhizogenes, has been investigated during the early stages of somatic embryo formation in suspension cultures of carrot (Daucus carota L.). The reporter gene GUS (Escherichia coli beta-glucuronidase), under transcriptional control of full-length rolB promoter region, has been utilized in order to evaluate both qualitative and quantitative variations in the expression pattern. Fluorimetric measurements point to the developmental regulation of the gene, while results from histochemical analysis indicate that the promoter of rolB is firstly activated in the central (core) region of the globular embryos.

Production of ribosome-inactivating protein from hairy root cultures of Luffa cylindrica (L.) Roem

Transformed root lines of Luffa cylindrica (L.) Roem. (Cucurbitaceae) were established by inoculation of in vitro grown plantlets with wild type Agrobacterium rhizogenes strain 1855. Cloned lines of hairy roots were tested for the presence of ribosome-inactivating proteins; crude extracts inhibited protein synthesis in a reaction mixture based on rabbit reticulocyte lysate. Inhibitory activity increased during culture period, reaching a maximum value in the stationary phase. No activity could be detected in the culture medium, nor in extracts from callus and/or suspension cultures. A ribosome-inactivating protein having specific activity of 62,100 U mg protein(-1) and a molecular mass of 26-28,000 Da was purified to homogeneity. The protein showed N-glycosidase activity on rat liver ribosomes. The results demonstrate that hairy root cultures can be successfully utilized for the in vitro production of ribosome-inactivating proteins.

Induction and growth properties of carrot roots with different complements of Agrobacterium rhizogenes T-DNA

Single and multiple infections of carrot discs were carried out with Agrobacterium strains harbouring different segments of pRi1855 TL-DNA cloned in the binary vector Bin 19 and with a strain carrying the TR-DNA from the same Ri plasmid. Roots induced by the various co-inoculations were cultured and their growth patterns were followed. Abundant roots could be induced by TL-DNA rol genes A, B and C as a single insert (rolA + B + C) and by rolB alone provided an extended segment beyond its 5' non-coding region was included in the construction. A depression of rooting capability was caused by the inclusion of rolC together with rolB (rolB + C). In all cases co-inoculation with the Agrobacterium carrying TR-DNA-borne auxin genes was necessary for root induction since none of the rol constructions was in itself capable of eliciting any response; an exceeding majority of these roots were however shown to contain rol genes but no TR-DNA. Rooting was also elicited if rol constructions were co-inoculated with a strain carrying TL-DNA genes 13 and 14 (ORF13 + 14) instead of the TR-DNA strain. These roots were shown to contain both rol genes and ORF13 + 14. Striking differences in growth properties were shown by roots containing different complements of TL-DNA genes. Typical hairy root traits, high growth rate, branching and, most noticeably, absence of geotropism, were shown by roots containing rolB alone, while roots with rolA + B + C were geotropic as normal carrot roots. Hairy root traits were conferred to rolA + B + C roots by the concomitant presence of ORF13 + 14 and by the addition of auxin to the culture medium. A model is presented which attempts to rationalize the growth patterns by assigning interplaying roles to the various TL-DNA genes involved.

Morphogenesis and Auxin Sensitivity of Transgenic Tobacco with Different Complements of Ri T-DNA

Leaf explants of hairy root tobacco (Nicotiana tabacum) regenerants characteristically differentiate roots from the wound margins on hormonefree medium. The same response can be elicited on normal tobacco by culturing the explants in the presence of auxin. We show here that the spontaneous rooting of transformed plants is neither due to the activity of right T-DNA-borne auxin genes nor to a substantially altered balance of endogenous hormones. Rather, an increased sensitivity to auxin is conferred to transformed cells by the left T-DNA (TL-DNA). Analysis of the morphogenetic behavior of transgenic tobacco plants obtained by transferring segments of TL-DNA cloned in a binary vector system allowed us to pinpoint TL-DNA genes responsible for this increased auxin sensitivity of hairy root tissues. Three genes (open reading frames 10, 11, 12) are responsible for the spontaneous rooting of leaf explants and confer to transgenic plants an exaggerated response to auxin.

Agrobacterium rhizogenes T-DNA genes capable of inducing hairy root phenotype

Segments of the TL-DNA of the agropine type Ri plasmid pRi 1855 encompassing single and groups of open-reading frames were cloned in the Ti plasmid-derived binary vector system Bin 19. Leaf disc infections on Nicotiana tabacum led to transformed plants, some of which showed typical hairy root phenotypes, such as the wrinkled leaf morphology, excessive and partially non geotropic root systems and the ability of leaf explants to differentiate roots in a hormone-free culture medium. Particularly interestingly, most of these traits were shown by plants transformed with a TL-DNA segment encompassing the single ORF 11, corresponding to the rolB locus. Hairy root can be induced by this latter T-DNA segment on wounded stems of tobacco plants; hairy root induction on carrot discs requires, on the contrary, a more complex complement of TL-DNA genes.

Hairy root transformation in alfalfa (Medicago sativa L.)

The widely cultivated forage legume alfalfa (Medicago sativa L.) was transformed with the agropine type Agrobacterium rhizogenes NCPPB 1855. Sterile root and callus cultures were derived from tumorous hairy roots which were easily obtained independent of the plant variety or genotype. Plant regeneration, via somatic embryogenesis, was achieved only when a selected alfalfa line, characterized by high regenerative capability, was utilized. Genetic transformation was confirmed by the presence of agropine and T-DNA. Phenotypic alterations, mainly affecting the root system, were observed in transformed plants. The possibility that T-DNA-induced variations could be useful in the improvement of M. sativa is discussed.

Conserved regions in the T-DNA of different Agrobacterium rhizogenes root-inducing plasmids

The T-regions of the three so far identified types of Ri plasmids-corresponding to the synthesis of three different hairy root opines, agropine, mannopine and cucumopine-have been compared in detail by Southern blot cross hybridizations. Two distinct zones of very strong sequence homology, approximately 4 and 3 kilobases in length respectively, have been identified in all three T-regions. The highly conserved sequences, not present in Ti plasmid T-DNA, may encode essential rhizogenic functions common to all Agrobacterium rhizogenes T-DNAs.

Identification of the genetic locus responsible for non-polar root induction by Agrobacterium rhizogenes 1855

Root proliferation can be induced by Agrobacterium rhizogenes on carrot discs both on the apical and basal surface (facing the root apex and base, respectively) or on the apical surface only, depending on the bacterial strain. This differential response on the two surfaces is denominated polarity. We correlate the polarity of some strains with the absence of an Ri plasmid genetic locus, present in non polar strains such as A. rhizogenes 1855, which bears sequence homology with the auxin genes of Ti plasmid T-DNA. We demonstrate that this locus is responsible for root induction on the basal surface since insertion of a transposon in this region of pRi1855 induces polarity in this strain.

Localization of agropine-synthesizing functions in the TR region of the root-inducing plasmid of Agrobacterium rhizogenes 1855

The region of the Ri plasmid pRi 1855 that encodes agropine synthesis has been identified through its sequence homology with the equivalent genes of the octopine Ti plasmid pTi ACH5. Interestingly the agropine genes lie outside the so-far identified T-DNA of pRi 1855, and are separated from this latter by a long sequence of non integrated plasmid DNA. The presence of this additional T-DNA (TRight DNA) in hairy roots was demonstrated by Southern blot analysis and by the presence of specific transcripts. The genes for agropine synthesis are arranged in the Ri plasmid in a reversed order as compared to their orientation in the Ti plasmid pTi ACH5.

Restriction endonuclease mapping of the root-inducing plasmid of Agrobacterium rhizogenes 1855

The root-inducing plasmid of the agropine type Agrobacterium rhizogenes 1855 was mapped by means of the restriction endonuclease EcoRI. The circular arrangement of the more than 60 fragments generated by this enzyme was established by electrophoretic analysis of pBR322 clones harboring overlapping segments of pRi1855 derived by partial digestion with EcoRI. A large region of the plasmid comprising the T-DNA was mapped with two additional enzymes, BamHI and HindIII, by means of Southern blot hybridizations between the fragments generated by the three enzymes.