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Biomedical subjects

D Inzé

Publications and source records attributed to D Inzé.

At least 19 recordsLinked to original sources
PubMed1997

Differential expression of CuZn- and Fe-superoxide dismutase genes of tobacco during development, oxidative stress, and hormonal treatments.

Chloroplasts of Nicotiana tabacum have two superoxide dismutases: a Fe- and a CuZn-containing enzyme, encoded by the nuclear genes sodB and sodCp, respectively. As a first step in studying the physiological function of these two enzymes, we compared the expression of sodB and sodCp in different plant organs, in response to hormonal treatments, and upon treatment with paraquat and Norflurazon. The sodCp transcript and active enzyme were detected only in young leaves of mature plants. The sodB transcript was more abundant in young compared to old leaves, but the enzymatic activity was higher in mature and senescent leaves. sodCp and sodB exhibited a different expression pattern upon treatment with abscisic acid, indole-3-acetic acid, kinetin, gibberellin, and 1-aminocyclopropane-1-carboxylate. Paraquat treatment caused a decrease in abundance of both transcripts, although the dose dependency of this decrease differed. Norflurazon-induced photooxidation resulted in a 10-fold increase of sodCp mRNA whereas the sodB transcript level was 25% higher than the control. These differences in expression might explain why both plastid-located superoxide dismutase enzymes are needed, particularly under stress conditions.

Amino Acid Sequence↗
PubMed1996

Identification of an Arabidopsis thaliana cDNA encoding a HSP70-related protein belonging to the HSP110/SSE1 subfamily.

Heat-shock protein 70 (HSP70)-related proteins are classified in two main subfamilies: the DnaK subfamily and the HSP110/SSE1 subfamily. We have characterized the first plant member of the HSP110/SSE1 subfamily, HSP91. At least two, tightly linked genes encoding HSP91 are present per haploid Arabidopsis genome. HSP91 is constitutively expressed in non-stressed Arabidopsis plants and is transiently induced by heat shock.

Amino Acid Sequence↗
PubMed1996

Plant cyclins: a unified nomenclature for plant A-, B- and D-type cyclins based on sequence organization.

The comparative analysis of a large number of plant cyclins of the A/B family has recently revealed that plants possess two distinct B-type groups and three distinct A-type groups of cyclins. Despite earlier uncertainties, this large-scale comparative analysis has allowed an unequivocal definition of plant cyclins into either A or B classes. We present here the most important results obtained in this study, and extend them to the case of plant D-type cyclins, in which three groups are identified. For each of the plant cyclin groups, consensus sequences have been established and a new, rational, plant-wide naming system is proposed in accordance with the guidelines of the Commission on Plant Gene Nomenclature. This nomenclature is based on the animal system indicating cyclin classes by an upper-case roman letter, and distinct groups within these classes by an arabic numeral suffix. The naming of plant cyclin classes is chosen to indicate homology to their closest animal class. The revised nomenclature of all described plant cyclins is presented, with their classification into groups CycA1, CycA2, CycA3, CycB1, CycB2, CycD1, CycD2 and CycD3.

Amino Acid Sequence↗
PubMed1996

G2-and early-M-specific expression of the NTCYC1 cyclin gene in Nicotiana tabacum cells.

We have previously reported the isolation of a cDNA encoding a mitotic cyclin, NTCYC1, from a tobacco cell suspension library. Here we describe the expression patterns of NTCYC1 and of Ntsuc1, a suc 1 plant homologue, in synchronized tobacco cell suspensions. Furthermore, the expression pattern of this cyclin is compared to that of Ntcdc2-1, a Nicotiana tabacum homologue of cdc2. While no NTCYC1 transcript was detected in cells synchronized in the G1 and S phases, NTCYC1 expression was observed in late G2 and early M phases, disappearing in the G1' of a new cell cycle. On the other hand, Ntsuc1 and Ntcdc2-1 exhibited a constitutive expression during the cell cycle. A functional analysis performed by microinjecting NTCYC1 mRNA into immature Xenopus oocytes, indicates that NTCYC1 could participate in the control of the G2/M transition in plant cells. Subsequently NTCYC1 expression was used to assess the status of mesophyll cells in expanded leaves of N. tabacum. Depending on leaf position along the shoot axis, a large population of mesophyll cells appeared with a 4C DNA content, suggesting a G2 arrest. It was found that leaves with such a population also contained high levels of NTCYC1 transcripts. With respect to these results concerning a naturally occurring G2-arrested cell population, the regulation of NTCYC1 expression in planta is discussed.

Amino Acid Sequence↗
PubMed1996

A molecular study of root-knot nematode-induced feeding sites.

In a compatible interaction, root-knot nematodes (Meloidogyne) induce a sophisticated feeding site shortly after they have penetrated the plant root. The feeding site contains metabolically highly active giant cells. To gain insight into the molecular aspects that are typical for giant cells, a cDNA library from tomato roots infected with Meloidogyne incognita was differentially screened to find induced genes. Among the genes identified, two extensin genes (Lemmi8 and Lemmi11) and a Lea-like gene (Lemmi9) were studied further.

Amino Acid Sequence↗
PubMed1996

The Arabidopsis cyclin-dependent kinase gene cdc2bAt is preferentially expressed during S and G2 phases of the cell cycle.

Cell cycle progression is regulated by cyclin-dependent kinases (CDKs). Arabidopsis thaliana contains two cdk genes, cdc2aAt and cdc2bAt. This paper compares the developmental and cell cycle phase-dependent transcription of both cdk genes. In situ hybridizations revealed that cdc2bAt steady-state mRNAs, much like cdc2aAt, are found both in meristematic cells and cells with a high proliferative competence. Cdc2aAt is expressed in every meristematic cell whereas cdc2bAt is found to be expressed in a patchy pattern. An even smaller number of meristematic cells express the mitotic cyc1At. These data indicate that cdc2bAt and cyc1At mRNAs accumulate in a particular cell cycle phase in agreement with evidence provided by hybridization experiments of flow cytometrysorted nuclei and the use of cell cycle blockers on roots. The data indicate that cdc2bAt is preferentially expressed in S and G2 phases whereas cdc2aAt expression is constitutive throughout the cell cycle, as shown previously. The existence of two distinct CDK classes in plants is proposed: (i) constitutively expressed CDKs containing a PSTAIRE motif (e.g. cdc2aAt) and (ii) CDKs with divergent motifs which are expressed during a limited interval of the cell cycle (e.g. cdc2bAt).

Arabidopsis↗
PubMed1996

Induction of cdc2a and cyc1At expression in Arabidopsis thaliana during early phases of nematode-induced feeding cell formation.

Root-knot and cyst nematodes are plant parasites that induce large multinucleated feeding cells in the roots of their hosts. Cytological observations have shown that root-knot nematodes induce giant cells by cycles of mitosis without cytokinesis whereas cyst nematodes provoke cell wall degradation leading to the formation of a large syncytium. This study was intended to characterize and compare the ability of both types of nematodes to induce progression through the cell cycle. For this purpose, the expression, upon nematode infection, of two cell cycle markers was followed: a marker for division competence, the cyclin-dependent kinase cdc2a and a marker for the G2 phase, the mitotic cyclin cyc1At. For both types of nematodes, transcriptional activation of these markers was correlated with early phases of feeding cell development. Using molecular markers, it was thus possible to confirm and extend the observations of repeated mitosis in root-knot nematode-induced giant cells. Surprisingly, promoter activation of both cdc2a and cyc1At markers was also found upon cyst nematode infection, in feeding cells in which mitosis has not been clearly reported. Incorporation of tritiated thymidine in these syncytia confirms that they progress through the S phase of the cell cycle. One possibility is that cyst nematodes induce cycles of DNA endoreduplication shunting the M phase. Despite obvious differences in ontogeny, common molecular mechanisms, involving cycles of DNA endoreduplication and cdc2a and cyc1At expression, might thus be involved in the formation of a giant cell or a syncytium.

Animals↗
PubMed1996

Tissue-specific expression conferred by the S-adenosyl-L-methionine synthetase promoter of Arabidopsis thaliana in transgenic poplar.

In Arabidopsis the promoter of the gene encoding S-adenosyl-L-methionine synthetase (SAM-S) Psam-1 confers expression preferentially in the vascular tissue. In search for promoters that drive expression in particular cells of the lignifying tissues in trees, we have analyzed the expression pattern conferred by the Psam-1 promoter in transgenic poplar. Histochemical analyses demonstrated beta-glucuronidase (GUS) activity mainly in phloem and cortex tissue throughout the plant, and in root tips. Fluorimetric assays showed high GUS activity in the tissues outside (phloem, cortex and cork) compared to those inside (xylem and pith) of the cambial layer. In contrast, the endogenous SAM-S activity was high in tissues inside and low in tissues outside of the cambial layer. RNA gel blot analysis demonstrated a high transcript level of the endogenous sam-s gene(s) in tissues both outside and inside the cambial layer. This indicates that the low SAM-S activity in the bark was at least partially due to translational and/or post-translational regulation of the endogenous sam-s gene(s). In dormant transgenics, the tissue specificity was conserved, but the activity levels were up to 10-fold reduced.

Arabidopsis↗
PubMed1996

A thiol protease and an anionic peroxidase are induced by lowering cytokinins during callus growth in Petunia.

We previously identified a group of proteins that increase early in Petunia hybrida calli subcultured on a low-cytokinin medium, unlike the calli subcultured on a high-cytokinin medium. The calli on the low-cytokinin medium do not regenerate (J.-P. Renaudin, C. Tournaire, B, Teyssendier de la Serve [1991] Physiol Plant 82: 48-56). Two of these proteins, P21 and P17, have been identified by peptide sequencing and cloned. P21 is highly homologous to a group of thiol proteases, including barely aleurain, rice oryzain gamma, Arabidopsis SAG2, and mammalian cathepsin H. P17 is highly homologous to a group of anionic peroxidases from potato and tomato. A study of their expression in two P. hybrida lines, PC6 and St40 which differ in their ability to regenerate, showed that the genes for P21 and P17 are differentially expressed depending on the type and the age of the organ, with the highest expression in senescing leaves and in aged calli. The data are in favor of these genes being associated with an early step of senescence, which may be due, in part, to a reduction in total cytokinin. The two Petunia lines are, thus, functionally different concerning the action of cytokinin in two developmental phenomena: in vitro organogenesis and senescence.

Amino Acid Sequence↗
PubMed1996

Tissue-specific activity of two manganese superoxide dismutase promoters in transgenic tobacco.

In eukaryotes, manganese superoxide dismutase is a nuclear-encoded protein that scavenges superoxide radicals in the mitochondrial matrix. We have isolated two manganese superoxide dismutase genes from Nicotiana plumbaginifolia L. and fused the 5' upstream regulatory region of these genes to the beta-glucuronidase reporter gene. The two gene fusions displayed a differential tissue specificity in transgenic tobacco (Nicotiana tabacum). Promoter activity of the SodA1 gene fusion was found in the pollen, middle layer, and stomium of anthers, but was usually undetectable in vegetative organs of mature plants. The SodA2 gene fusion was expressed in the leaves, stems, roots, and flowers. SodA2 promoter activity was most prominent in the vascular bundles, stomata, axillary buds, pericycle, stomium, and pollen. Histochemical analysis of succinate dehydrogenase activity suggested that the spatial expression of the two gene fusions is generally correlated with mitochondrial respiratory activity.

Biological Transport↗
PubMed1996

Enhancement of oxidative stress tolerance in transgenic tobacco plants overproducing Fe-superoxide dismutase in chloroplasts.

A chimeric gene consisting of the coding sequence for chloroplastic Fe superoxide dismutase (FeSOD) from Arabidopsis thaliana, coupled to the chloroplast targeting sequence from the pea ribulose-1,5-bisphosphate carboxylase/oxygenase small subunit, was expressed in Nicotiana tabacum cv Petit Havana SR1. Expression of the transgenic FeSOD protected both the plasmalemma and photosystem II against superoxide generated during illumination of leaf discs impregnated with methyl viologen. By contrast, overproduction of a mitochondrial MnSOD from Nicotiana plumbaginifolia in the chloroplasts of cv SR1 protected only the plasmalemma, but not photosystem II, against methyl viologen (L. Slooten, K. Capiau, W. Van Camp, M. Van Montagu, C. Sybesma, D. Inzé [1995] Plant Physiol 107: 737-750). The difference in effectiveness correlates with different membrane affinities of the transgenic FeSOD and MnSOD. Overproduction of FeSOD does not confer tolerance to H2O2, singlet oxygen, chilling-induced photoinhibition in leaf disc assays, or to salt stress at the whole plant level. In nontransgenic plants, salt stress led to a 2- to 3-fold increase in activity, on a protein basis, of FeSOD, cytosolic and chloroplastic Cu/ZnSOD, ascorbate peroxidase, dehydroascorbate reductase, and glutathione reductase. In FeSOD-overproducing plants under salt stress, the induction of cytosolic and chloroplastic Cu/ZnSOD was suppressed, whereas induction of a water-soluble chloroplastic ascorbate peroxidase isozyme was promoted.

Adaptation, Physiological↗
PubMed1995

Molecular characterization of a putative Arabidopsis thaliana copper transporter and its yeast homologue.

At the molecular level, little is known about the transport of copper across plant membranes. We have isolated an Arabidopsis thaliana cDNA by complementation of a mutant (ctr1-3) of Saccharomyces cerevisiae defective in high affinity copper uptake. This cDNA codes for a highly hydrophobic protein (COPT1) of 169 amino acid residues and with three putative transmembrane domains. Most noteworthy, the first 44 residues display significant homology to the methionine- and histidine-rich copper binding domain of three bacterial copper binding proteins, among these a copper transporting ATPase. Mutant yeast cells expressing COPT1 exhibit nearly wild type behavior with regard to growth on a nonfermentable carbon source and resistance to copper and iron starvation. Expression of COPT1 is also associated with an increased sensitivity to copper toxicity. Additionally, COPT1 shows significant homology to an open reading frame of 189 amino acid residues on yeast chromosome VIII. This gene (CTR2) may encode an additional yeast metal transporter able to mediate the uptake of copper. A mutation in CTR2 displays a higher level of resistance to toxic copper concentrations. Overexpression of CTR2 provides increased resistance to copper starvation and is also associated with an increased sensitivity to copper toxicity. The amino acid sequence of CTR2, like Arabidopsis COPT1, contains three potential transmembrane domains. Taken together, the data suggest that a plant metal transporter, which is most likely involved in the transport of copper, has been identified.

Amino Acid Sequence↗
PubMed1995

Characterization of Arabidopsis thaliana cDNAs that render yeasts tolerant toward the thiol-oxidizing drug diamide.

Diamide oxidizes cellular thiols and induces oxidative stress. To isolate plant genes which may, when overexpressed, increase tolerance of plants toward oxidative damage, an in vivo diamide tolerance screening in yeasts was used. An Arabidopsis cDNA library in a yeast expression vector was used to transform a yeast strain with intact antioxidant defense. Cells from approximately 10(5) primary transformants were selected for resistance to diamide. Three Arabidopsis cDNAs which confer diamide tolerance were isolated. This drug tolerance was specific and no cross tolerance toward hydroperoxides was found. One cDNA (D3) encodes a polypeptide which has an amino-terminal J domain characteristic of a divergent family of DnaJ chaperones. Another (D18) encodes a putative dTDP-D-glucose 4,6-dehydratase. Surprisingly, the third cDNA (D22) encodes a plant homolog of gamma-glutamyltransferases. It would have been difficult to predict that the expression of those genes would lead to an improved survival under conditions of depletion of cellular thiols. Hence, we suggest that this cloning approach may be a useful contribution to the isolation of plant genes that can help to cope with oxidative stress.

Amino Acid Sequence↗
PubMed1995

Molecular characterization of an Arabidopsis thaliana cDNA encoding a novel putative adenylate translocator of higher plants.

We have isolated an Arabidopsis thaliana cDNA encoding a highly hydrophobic membrane protein of 589 amino acids which contains 12 potential transmembrane helices and shows a high degree of similarity (43.5% identity, 66.2% similarity) to the ATP/ADP translocase of the Gram-negative bacterium Rickettsia prowazekii, an obligate intracellular parasite responsible for the epidemic typhus. This rickettsial translocator resides in the cytoplasmic membrane and allows the bacterium to exploit the host cytoplasmic ATP pool. We hypothesize that the A. thaliana homolog of the R. prowazekii ATP/ADP translocase is the functional eukaryotic equivalent and resides in the plastid inner envelope membrane where it functions as an ATP importer.

Arabidopsis↗
PubMed1995

Arabidopsis thaliana NADPH oxidoreductase homologs confer tolerance of yeasts toward the thiol-oxidizing drug diamide.

To isolate new plant genes involved in the defense against oxidative stress, an Arabidopsis cDNA library in a yeast expression vector was transformed into a yeast strain deficient in the YAP1 gene, which encodes a b-Zip transcription factor and regulates general stress response in yeasts. Cells from approximately 10(5) primary transformants were subjected to a tolerance screen toward the thiol-oxidizing drug diamide, which depletes the reduced glutathione in the cell. Four types of Arabidopsis cDNAs were isolated. Three of these cDNAs (P1, P2, and P4) belong to a plant zeta-crystallin family and P3 is an Arabidopsis homolog of isoflavonoid reductases. As such, all four isolated cDNAs are homologous to NADPH oxidoreductases. P1, P2, and P3 steady-state mRNAs accumulated rapidly in Arabidopsis plants under various oxidative stress conditions, such as treatment with paraquat, t-butylhydroperoxide, diamide, and menadione. The data suggested that proteins encoded by the isolated cDNAs play a distinct role in plant antioxidant defense and are possibly involved in NAD(P)/NAD(P)H homeostasis.

Amino Acid Sequence↗
PubMed1995

Dominant negative mutants of the Cdc2 kinase uncouple cell division from iterative plant development.

Because plant cells do not move and are surrounded by a rigid cell wall, cell division rates and patterns are believed to be directly responsible for generating new structures throughout development. To study the relationship between cell division and morphogenesis, transgenic tobacco and Arabidopsis plants were constructed expressing dominant mutations in a key regulator of the Arabidopsis cell cycle, the Cdc2a kinase. Plants constitutively overproducing the wild-type Cdc2a or the mutant form predicted to accelerate the cell cycle did not exhibit a significantly altered development. In contrast, a mutation expected to arrest the cell cycle abolished cell division when expressed in Arabidopsis, whereas some tobacco plants constitutively producing this mutant protein were recovered. These plants had a reduced histone H1 kinase activity and contained considerably fewer cells. These cells were, however, much larger and underwent normal differentiation. Morphogenesis, histogenesis and developmental timing were unaffected. The results indicate that, in plants, the developmental controls defining shape can act independently from cell division rates.

Amino Acid Sequence↗