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PubMed1998

A two-component system plays an important role in the root-colonizing ability of Pseudomonas fluorescens strain WCS365.

We describe the characterization of a novel Tn5lacZ colonization mutant of the efficiently colonizing Pseudomonas fluorescens strain WCS365, mutant strain PCL1210, which is at least 300- to 1,000-fold impaired in colonization of the potato root tip after co-inoculation of potato stem cuttings with a 1:1 mixture of mutant and parental cells. Similarly, the mutant is also impaired in colonization of tomato, wheat, and radish, indicating that the gene involved plays a role in the ability of P. fluorescens WCS365 to colonize a wide range of plant species. A 3.1-kb DNA fragment was found to be able to complement the observed mutation. The nucleotide sequence of the region around the Tn5lacZ insertion showed three open reading frames (ORFs). The transcriptional start site was determined. The operon is preceded by an integration host factor (IHF) binding site consensus sequence whereas no clear -10 and -35 sequences are present. The deduced amino acid sequences of the first two genes of the operon, designated as colR and colS, show strong similarity with known members of two-component regulatory systems. ColR has homology with the response regulators of the OmpR-PhoB subclass whereas ColS, the product of the gene in which the mutation resides, shows similarity to the sensor kinase members of these two-component systems. Hydrophobicity plots show that this hypothetical sensor kinase has two transmembrane domains, as is also known for other sensor kinases. The product of the third ORF, Orf222, shows no homology with known proteins. Only part of the orf222 gene is present in the colonization-complementing, 3.1-kb region, and it therefore does not play a role in complementation. No experimental evidence for a role of the ColR/ColS two-component system in the suspected colonization traits chemotaxis and transport of exudate compounds could be obtained. The function of this novel two-component system therefore remains to be elucidated. We conclude that colonization is an active process in which an environmental stimulus, through this two-component system, activates a so far unknown trait that is crucial for colonization.

Amino Acid Sequence↗
PubMed2006

Adenosine diphosphate ribosylation of dinitrogenase reductase and adenylylation of glutamine synthetase control ammonia excretion in ethylenediamine-resistant mutants of Azospirillum brasilense Sp7.

Azospirillum brasilense is a nitrogen-fixing, root-colonizing bacterium that brings about plant-growth-promoting effects mainly because of its ability to produce phytohormones. Ethylenediamine (EDA)-resistant mutants of A. brasilense were isolated and screened for their higher ability to decrease acetylene and release ammonia in the medium. One of the mutants showed considerably higher levels of acetylene decrease and ammonia excretion. Nitrogenase activity of this mutant was relatively resistant to inhibition by NH(4)Cl. Adenosine triphosphate ribosylation of dinitrogenase reductase in the mutant did not increase even in presence of 10 mM NH(4)Cl. Although the mutant showed decreased glutamine synthetase (GS) activity, neither the levels of GS synthesized by the mutant nor the NH (4) (+) -binding site in the GS differed from those of the parent. The main reason for the release of ammonia by the mutant seems to be the fixation of higher levels of nitrogen than its GS can assimilate, as well as higher levels of adenylylation of GS, which may decrease ammonia assimilation.

Adenosine Diphosphate Ribose↗
PubMed2001

BDNF but not NT-4 is required for normal flexion reflex plasticity and function.

Neurotrophins can directly modulate the function of diverse types of central nervous system synapses. Brain-derived neurotrophic factor (BDNF) might be released by nociceptors onto spinal neurons and mediate central sensitization associated with chronic pain. We have studied the role of BDNF and neurotrophin-4 (NT-4), both ligands of the trkB tyrosine kinase receptor, in synaptic transmission and reflex plasticity in the mouse spinal cord. We used an in vitro spinal cord preparation to measure monosynaptic and polysynaptic reflexes evoked by primary afferents in BDNF- and NT-4-deficient mice. In situ hybridization studies show that both these neurotrophins are synthesized by sensory neurons, and NT-4, but not BDNF, also is expressed by spinal neurons. BDNF null mutants display selective deficits in the ventral root potential (VRP) evoked by stimulating nociceptive primary afferents whereas the non-nociceptive portion of the VRP remained unaltered. In addition, activity-dependent plasticity of the VRP evoked by repetitive (1 Hz) stimulation of nociceptive primary afferents (termed wind-up) was substantially reduced in BDNF-deficient mice. This plasticity also was reduced in a reversible manner by the protein kinase inhibitor K252a. Although the trkB ligand NT-4 is normally present, reflex properties in NT-4 null mutant mice were normal. Pharmacological studies also indicated that spinal N-methyl-d-aspartate receptor function was unaltered in BDNF-deficient mice. Using immunocytochemistry for markers of nociceptive neurons we found no evidence that their number or connectivity was substantially altered in BDNF-deficient mice. Our data therefore are consistent with a direct role for presynaptic BDNF release from sensory neurons in the modulation of pain-related neurotransmission.

Animals↗
PubMed2004

Altered primary afferent anatomy and reduced thermal sensitivity in mice lacking galectin-1.

The transmission of nociceptive information occurs along non-myelinated, or thinly myelinated, primary afferent axons. These axons are generally classified as peptidergic (CGRP-expressing) or non-peptidergic (IB4-binding), although there is a sub-population that is both CGRP-positive and IB4-binding. During neuronal development and following injury, trophic factors and their respective receptors regulate their survival and repair. Recent reports also show that the carbohydrate-binding protein galectin-1 (Gal1), which is expressed by nociceptive primary afferent neurons during development and into adulthood, is involved in axonal pathfinding and regeneration. Here we characterize anatomical differences in dorsal root ganglia (DRG) of Gal1 homozygous null mutant mice (Gal1(-/-)), as well as behavioural differences in tests of nociception. Gal1(-/-) mice have a significantly reduced proportion of IB4-binding DRG neurons, an increased proportion of NF200-immunoreactive DRG neurons, increased depth of central terminals of IB4-binding and CGRP-immunoreactive axons in the dorsal horn, and a reduced number of Fos-positive second order neurons following thermal (cold or hot) stimulation. While there is no difference in the total number of axons in the dorsal root of Gal1(-/-) mice, there are an increased number of myelinated axons, suggesting that in the absence of Gal1, neurons that are normally destined to become IB4-binding instead become NF200-expressing. In addition, mice lacking Gal1 have a decreased sensitivity to noxious thermal stimuli. We conclude that Gal1 is involved in nociceptive neuronal development and that the lack of this protein results in anatomical and functional deficits in adulthood.

Afferent Pathways↗
PubMed1999

Gravitropism of inflorescence stems in starch-deficient mutants of Arabidopsis.

Previous studies have assayed the gravitropic response of roots and hypocotyls of wild type Arabidopsis thaliana, two reduced-starch strains, and a starchless strain. Because there have been few reports on inflorescence gravitropism, in this article, we use microscopic analyses and time-course studies of these mutants and their wild type to study gravitropism in these stems. Sedimentation of plastids was observed in endodermal cells of the wild type and reduced-starch mutants but not in the starchless mutant. In all of these strains, the short inflorescence stems (1.0-2.9 cm) were less responsive to the gravistimulus compared with the long stems (3.0-6.0 cm). In both long and short inflorescence stems, the wild type initially had the greatest response; the starchless mutant had the least response; and the reduced starch mutants exhibited an intermediate response. Furthermore, growth rates among all four strains were approximately equal. At about 6 h after reorientation, inflorescences of all strains returned to a position parallel to the gravity vector. Thus, in inflorescence stems, sedimentation of plastids may act as an accelerator but is not required to elicit a gravitropic response. Furthermore, the site of perception appears to be diffuse throughout the inflorescence stem. These results are consistent with both a plastid-based statolith model and the protoplast pressure hypothesis, and it is possible that multiple systems for gravity perception occur in plant cells.

Arabidopsis↗
PubMed1996

Genetic analysis of the effects of polar auxin transport inhibitors on root growth in Arabidopsis thaliana.

Polar auxin transport inhibitors, including N-1-naphthylphthalamic acid (NPA) and 2,3,5-triiodobenzoic acid (TIBA), have various effects on physiological and developmental events, such as the elongation and tropism of roots and stems, in higher plants. We isolated NPA-resistant mutants of Arabidopsis thaliana, with mutations designated pir1 and pir2, that were also resistant to TIBA. The mutations specifically affected the root-elongation process, and they were shown ultimately to be allelic to aux1 and ein2, respectively, which are known as mutations that affect responses to phytohormones. The mechanism of action of auxin transport inhibitors was investigated with these mutants, in relation to the effects of ethylene, auxin, and the polar transport of auxin. With respect to the inhibition of root elongation in A. thaliana, we demonstrated that (1) the background level of ethylene intensifies the effects of auxin transport inhibitors, (2) auxin transport inhibitors might act also via an inhibitory pathway that does not involve ethylene, auxin, or the polar transport of auxin, (3) the hypothesis that the inhibitory effect of NPA on root elongation is due to high-level accumulation of auxin as a result of blockage of auxin transport is not applicable to A. thaliana, and (4) in contrast to NPA, TIBA itself has a weak auxin-like inhibitory effect.

Arabidopsis↗
PubMed2002

Cytokinin growth responses in Arabidopsis involve the 26S proteasome subunit RPN12.

The 26S proteasome is an ATP-dependent eukaryotic protease responsible for degrading many important cell regulators, especially those conjugated with multiple ubiquitins. Bound on both ends of the 20S core protease is a multisubunit regulatory particle that plays a crucial role in substrate selection by an as yet unknown mechanism(s). Here, we show that the RPN12 subunit of the Arabidopsis regulatory particle is involved in cytokinin responses. A T-DNA insertion mutant that affects RPN12a has a decreased rate of leaf formation, reduced root elongation, delayed skotomorphogenesis, and altered growth responses to exogenous cytokinins, suggesting that the mutant has decreased sensitivity to the hormone. The cytokinin-inducible genes CYCD3 and NIA1 are upregulated constitutively in rpn12a-1, indicating that feedback-inhibitory mechanisms also may be altered. rpn12a-1 seedlings also showed changes in auxin-induced growth responses, further illustrating the close interaction between auxin and cytokinin regulation. In yeast, RPN12 is necessary for the G1/S and G2/M transitions of the cell cycle, phases that have been shown to be under cytokinin control in plants. We propose that RPN12a is part of the Arabidopsis 26S proteasome that controls the stability of one or more of the factors involved in cytokinin regulation.

Adenine↗
PubMed1998

A new genetic locus in sinorhizobium meliloti is involved in stachydrine utilization

Stachydrine, a betaine released by germinating alfalfa seeds, functions as an inducer of nodulation genes, a catabolite, and an osmoprotectant in Sinorhizobium meliloti. Two stachydrine-inducible genes were found in S. meliloti 1021 by mutation with a Tn5-luxAB promoter probe. Both mutant strains (S10 and S11) formed effective alfalfa root nodules, but neither grew on stachydrine as the sole carbon and nitrogen source. When grown in the absence or presence of salt stress, S10 and S11 took up [14C]stachydrine as well as wild-type cells did, but neither used stachydrine effectively as an osmoprotectant. In the absence of salt stress, both S10 and S11 took up less [14C]proline than wild-type cells did. S10 and S11 appeared to colonize alfalfa roots normally in single-strain tests, but when mixed with the wild-type strain, their rhizosphere counts were reduced more than 50% (P </= 0.01) relative to the wild type. These results suggest that stachydrine catabolism contributes to root colonization. DNA sequence analysis identified the mutated locus in S11 as putA, and the luxAB fusion in that gene was induced by proline as well as stachydrine. DNA that restored the capacity of mutant S10 to catabolize stachydrine contained a new open reading frame, stcD. All data are consistent with the concept that stcD codes for an enzyme that produces proline by demethylation of N-methylproline, a degradation product of stachydrine.

Journal Article↗
PubMed2004

An energy taxis transducer promotes root colonization by Azospirillum brasilense.

Motility responses triggered by changes in the electron transport system are collectively known as energy taxis. In Azospirillum brasilense, energy taxis was shown to be the principal form of locomotor control. In the present study, we have identified a novel chemoreceptor-like protein, named Tlp1, which serves as an energy taxis transducer. The Tlp1 protein is predicted to have an N-terminal periplasmic region and a cytoplasmic C-terminal signaling module homologous to those of other chemoreceptors. The predicted periplasmic region of Tlp1 comprises a conserved domain that is found in two types of microbial sensory receptors: chemotaxis transducers and histidine kinases. However, the function of this domain is currently unknown. We characterized the behavior of a tlp1 mutant by a series of spatial and temporal gradient assays. The tlp1 mutant is deficient in (i) chemotaxis to several rapidly oxidizable substrates, (ii) taxis to terminal electron acceptors (oxygen and nitrate), and (iii) redox taxis. Taken together, the data strongly suggest that Tlp1 mediates energy taxis in A. brasilense. Using qualitative and quantitative assays, we have also demonstrated that the tlp1 mutant is impaired in colonization of plant roots. This finding supports the hypothesis that energy taxis and therefore bacterial metabolism might be key factors in determining host specificity in Azospirillum-grass associations.

Amino Acid Sequence↗
PubMed2006

Solubilization of potassium-bearing minerals by a wild-type strain of Bacillus edaphicus and its mutants and increased potassium uptake by wheat.

Two potassium (K)-bearing minerals, Nanjing feldspar and Suzhou illite, were used to investigate K mobilization by the wild-type strain NBT of Bacillus edaphicus, also labeled MPs+, selected for high activity in mobilizing potassium from minerals, and by four of its UV + LiCl mutants, MPs++, MPs+1, MPs+2, and MPs-. In liquid cultures, the five bacterial strains showed better growth on Suzhou illite than on Nanjing feldspar. Suzhou illite was the better potassium source for the growth of the wild type and the MPs++, MPs+1, and MPs+2 mutants. Solubilization of K from its sources by the wild-type NBT and the MPs++ mutant resulted mostly from the action of organic acids and capsular polysaccharides. Oxalic acid seemed to be a more active agent for the solubilization of Nanjing feldspar. Oxalic and tartaric acids were likely involved in the solubilization of Suzhou illite. The MPs- mutant did not produce any organic acid or capsular polysaccharide when grown on the above two K sources. In a pot experiment, wheat (Triticum aestivum L.) 'Yangmai-158' was grown in a yellow-brown soil that had low available K. After inoculation with bacterial strains, B. edaphicus NBT and its four mutants, MPs++, MPs+1, MPs+2, and MPs- (in separate tests), the root growth and shoot growth of wheat were significantly increased by B. edaphicus NBT and the mutants MPs++ and MPs+1. Bacterial inoculation also resulted in significantly higher N, P, and K contents of plant components. The bacteria were able to survive in the wheat rhizosphere soils after root inoculation.

Bacillus↗
PubMed2000

The molecular physiology of ammonium uptake and retrieval.

Plants are able to take up ammonium from the soil, or through symbiotic interactions with microorganisms, via the root system. Using functional complementation of yeast mutants, it has been possible to identify a new class of membrane proteins, the ammonium transporter/methylammonium permease (AMT/MEP) family, that mediate secondary active ammonium uptake in eukaryotic and prokaryotic organisms. In plants, the AMT gene family can be subdivided according to their amino-acid sequences into three subfamilies: a large subfamily of AMT1 genes and two additional subfamilies each with single members (LeAMT1;3 from tomato and AtAMT2;1 from Arabidopsis thaliana). These transporters vary especially in their kinetic properties and regulatory mechanism. High-affinity transporters are induced in nitrogen-starved roots, whereas other transporters may be considered as the 'work horses' that are active when conditions are conducive to ammonium assimilation. The expression of several AMTs in root hairs further supports a role in nutrient acquisition. These studies provide basic information that will be needed for the dissection of nitrogen uptake by plants at the molecular level and for determining the role of individual AMTs in nutrient uptake and potentially in nutrient efficiency.

Biological Transport↗
PubMed1998

Characterization of the hcnABC gene cluster encoding hydrogen cyanide synthase and anaerobic regulation by ANR in the strictly aerobic biocontrol agent Pseudomonas fluorescens CHA0.

The secondary metabolite hydrogen cyanide (HCN) is produced by Pseudomonas fluorescens from glycine, essentially under microaerophilic conditions. The genetic basis of HCN synthesis in P. fluorescens CHA0 was investigated. The contiguous structural genes hcnABC encoding HCN synthase were expressed from the T7 promoter in Escherichia coli, resulting in HCN production in this bacterium. Analysis of the nucleotide sequence of the hcnABC genes showed that each HCN synthase subunit was similar to known enzymes involved in hydrogen transfer, i.e., to formate dehydrogenase (for HcnA) or amino acid oxidases (for HcnB and HcnC). These similarities and the presence of flavin adenine dinucleotide- or NAD(P)-binding motifs in HcnB and HcnC suggest that HCN synthase may act as a dehydrogenase in the reaction leading from glycine to HCN and CO2. The hcnA promoter was mapped by primer extension; the -40 sequence (TTGGC ... ATCAA) resembled the consensus FNR (fumarate and nitrate reductase regulator) binding sequence (TTGAT ... ATCAA). The gene encoding the FNR-like protein ANR (anaerobic regulator) was cloned from P. fluorescens CHA0 and sequenced. ANR of strain CHA0 was most similar to ANR of P. aeruginosa and CydR of Azotobacter vinelandii. An anr mutant of P. fluorescens (CHA21) produced little HCN and was unable to express an hcnA-lacZ translational fusion, whereas in wild-type strain CHA0, microaerophilic conditions strongly favored the expression of the hcnA-lacZ fusion. Mutant CHA21 as well as an hcn deletion mutant were impaired in their capacity to suppress black root rot of tobacco, a disease caused by Thielaviopsis basicola, under gnotobiotic conditions. This effect was most pronounced in water-saturated artificial soil, where the anr mutant had lost about 30% of disease suppression ability, compared with wild-type strain CHA0. These results show that the anaerobic regulator ANR is required for cyanide synthesis in the strictly aerobic strain CHA0 and suggest that ANR-mediated cyanogenesis contributes to the suppression of black root rot.

Aerobiosis↗
PubMed1999

Tomato seed and root exudate sugars: composition, utilization by Pseudomonas biocontrol strains and role in rhizosphere colonization.

The role of tomato seed and root exudate sugars as nutrients for Pseudomonas biocontrol bacteria was studied. To this end, the major exudate sugars of tomato seeds, seedlings and roots were identified and quantified using high-performance liquid chromatographic (HPLC) analysis. Glucose, fructose and maltose were present in all studied growth stages of the plant, but the ratios of these sugars were strongly dependent on the developmental stage. In order to study the putative role of exudate sugar utilization in rhizosphere colonization, two approaches were adopted. First, after co-inoculation on germinated tomato seeds, the root-colonizing ability of the efficient root-colonizing P. fluorescens strain WCS365 in a gnotobiotic quartz sand-plant nutrient solution system was compared with that of other Pseudomonas biocontrol strains. No correlation was observed between the colonizing ability of a strain and its ability to use the major exudate sugars as the only carbon and energy source. Secondly, a Tn5lacZ mutant of P. fluorescens strain WCS365, strain PCL1083, was isolated, which is impaired in its ability to grow on simple sugars, including those found in exudate. The mutation appeared to reside in zwf, which encodes glucose-6-phosphate dehydrogenase. The mutant grows as well as the parental strain on other media, including tomato root exudate. After inoculation of germinated sterile tomato seeds, the mutant cells reached the same population levels at the root tip as the wild-type strain, both alone and in competition, indicating that the ability to use exudate sugars does not play a major role in tomato root colonization, despite the fact that sugars have often been reported to represent the major exudate carbon source. This conclusion is supported by the observation that the growth of mutant PCL1083 in vitro is inhibited by glucose, a major exudate sugar, at a concentration of 0.001%, which indicates that the glucose concentration in the tomato rhizosphere is very low.

Carbohydrate Metabolism↗
PubMed2001

Competitiveness in root colonization by Pseudomonas putida requires the rpoS gene.

The rpoS gene in Pseudomonas putida was essential for plant root colonization under competitive conditions from other microbes. The RpoS- mutant survived less well than the wild-type strain in culture medium, and unlike the wild-type, failed to colonize the roots in a peat matrix containing an established diverse microflora. The RpoS-deficient P. putida isolate was generated by insertion of a glucuronidase-npt cassette into the rpoS gene. The RpoS mutant had dose-dependent increased sensitivity to oxidative stress and produced Mn-superoxide dismutase activity earlier than the parent. While extracts from wild-type P. putida stationary-phase cells contained three isozymes of catalase (CatA, CatB, and CatC), the sigma38-deficient P. putida lacked CatB. These results are consistent with previous findings that CatB is induced in stationary-phase.

Bacterial Proteins↗
PubMed2004

Site-specific effect of ascorbic acid deficiency on the structure and function of odontoblasts in the teeth of osteogenic disorder rat in vivo.

The influence of chronic L-ascorbic acid (AsA) deficiency on dentinogenesis was examined in Osteogenic Disorder Shionogi (ODS) rat, which bear inborn lack of L-gulonolactone oxidase. Weanling male rats were kept on AsA-free diet for 4 weeks until all suffered from scurvy. Control rats were given AsA in drinking water. The dentin of molars and incisors of the scorbutic rats was thinner than that in control, except for the crown-analogue (enamel-related) of incisors. Predentin in scorbutic molars showed irregular thickness, and was almost lacking in roots. In the root-analogue (cementum-related) region of scorbutic incisors, dentin displayed metachromatic incremental lines, and the thickened predentin contained collagen fibrils of irregular diameter. The odontoblasts facing the affected regions contained dilated rough endoplasmic reticulum cisternae. In the crown-analogue of scorbutic incisors, however, dentin, predentin, and odontoblasts were comparable to those of controls. These data indicate that AsA deficiency differentially affects the synthetic and/or secretory activity of odontoblasts in ODS rat teeth in a site-specific manner. The regional differences implicate the presence of putative local factor(s) in the crown-analogue of incisors that might have compensated for AsA deficiency. The odontoblasts in the crown-analogue of incisors may have different requirements for AsA from those in molars and the root-analogue of incisors.

Animals↗
PubMed2002

Age-related loss of rooting capability in Arabidopsis thaliana and its reversal by peptides containing the Arg-Gly-Asp (RGD) motif.

We describe here an experimental system to study the age-related decline of adventitious root formation in Arabidopsis thaliana L. (Heynh), ecotype Landsberg erecta (Ler). The system is based on the different rooting capacity of hypocotyls from de-rooted juvenile (12-day-old) and adult (26-day-old) plants. Hypocotyls from de-rooted juvenile plants rooted readily within a week of culture, and the rooting process was not dependent on exogenous auxin. In contrast, hypocotyls from de-rooted adult plants rooted poorly and only after longer periods of time. Exogenously applied auxin had no effect on rooting of hypocotyls from de-rooted adult plants. Rooting capacity, although correlated with the transition to flowering, did not depend on this transition. Root induction declined in a similar manner when the transition to flowering was delayed, either genetically with the fve mutant or physiologically with short days. The results showed that rooting of hypocotyls from de-rooted adult plants depended on the effect of peptides containing the RGD motif. Both the percentage of rooting and the number of roots were largely increased when the hypocotyls were treated transiently with the RGD peptide. The effect of the RGD peptide was a necessary, but not sufficient, condition for rooting of hypocotyls from de-rooted adult plants.

Journal Article↗
PubMed1990

Physiological Characteristics of Fe Accumulation in the ;Bronze' Mutant of Pisum sativum L., cv ;Sparkle' E107 (brz brz).

The pea (Pisum sativum L.) mutant, E107 (brz, brz) accumulated extremely high concentrations of Fe in its older leaves when grown in light rooms in either defined nutrient media or potting mix, or outdoors in soil. Leaf symptoms (bronze color and necrosis) were correlated with very high Fe concentrations. When E107 plants were grown in nutrient solutions supplied 10 mum Fe, as the Fe(III)-N,N'-ethylenebis[2-(2-hydroxyphenyl)glycine] chelate, their roots released higher concentrations of Fe(III) reducing substances to the nutrient media than did roots of the normal parent cv, ;Sparkle.' Reciprocal grafting experiments demonstrated that the high concentrations of Fe in the shoot was controlled by the genotype of the root. In short-term (59)Fe uptake studies, 15-day-old E107 seedlings exhibited higher rates of Fe absorption than did ;Sparkle' seedlings under Fe-adequate growth conditions. Iron deficiency induced accelerated short-term Fe absorption rates in both mutant and normal genotypes. Iron-treated E107 roots also released larger amounts of both protons and Fe(III) reductants into their nutrient media than did iron-treated ;Sparkle' roots. Furthermore, the mutant translocated proportionately more Fe to its shoot than did the parent regardless of Fe status.

Journal Article↗
PubMed1983

Genetic analysis of T-DNA transcripts in nopaline crown galls.

Plant crown gall tumor cells result from the insertion and expression of a defined DNA sequence, called T-DNA, which is derived from the Ti plasmid, harbored by Agrobacterium tumefaciens strains. To study the function of the genes of the T-DNA of the nopaline Ti plasmid, pTiC58, a collection of mutants was isolated so that T-DNA genes are inactivated either separately or in various combinations. It was found that no single T-DNA gene or T-region border is absolutely essential for stable tumor formation. We have identified the gene responsible for synthesis in transformed cells of the phosphorylated sugar, agrocinopine, and at least three additional genes controlling the morphology of plant tumors. Two of these latter genes work together to inhibit shoot formation and ensure efficient tumorous growth. Inactivation of these genes can be suppressed by the addition of auxins. The third gene inhibits root formation and appears to play a role in the cytokinin-independent growth of transformed cells. Mutants missing all three genes do not induce tumors, nor shoot or root formation, although the mutant T-DNA sequence is transferred to plant cells.

Arginine↗