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F Meins

Publications and source records attributed to F Meins.

At least 55 records · Page 3Linked to original sources
PubMed1991

High-level expression of a tobacco chitinase gene in Nicotiana sylvestris. Susceptibility of transgenic plants to Cercospora nicotianae infection.

Endochitinases (E.C.3.2.14, chitinase) are believed to be important in the biochemical defense of plants against chitin-containing fungal pathogens. We introduced a gene for class I (basic) tobacco chitinase regulated by Cauliflower Mosaic Virus 35S-RNA expression signals into Nicotiana sylvestris. The gene was expressed to give mature, enzymatically active chitinase targeted to the intracellular compartment of leaves. Most transformants accumulated extremely high levels of chitinase-up to 120-fold that of non-transformed plants in comparable tissues. Unexpectedly, some transformants exhibited chitinase levels lower than in non-transformed plants suggesting that the transgene inhibited expression of the homologous host gene. Progeny tests indicate this effect is not permanent. High levels of chitinase in transformants did not substantially increase resistance to the chitin-containing fungus Cercospora nicotiana, which causes Frog Eye disease. Therefore class I chitinase does not appear to be the limiting factor in the defense reaction to this pathogen.

Base Sequence↗
PubMed1991

Differential Regulation of beta-1,3-Glucanase Messenger RNAs in Response to Pathogen Infection.

The acidic, extracellular, glucan endo-1,3-beta-glucosidases (EC 3.2.1.39; beta-1,3-glucanases), pathogenesis-related proteins-2, -N, and -O (i.e. PR-2, PR-N, and PR-O) were purified from Nicotiana tabacum (tobacco) and their partial amino acid sequences determined. Based on these data, complementary DNA (cDNA) clones encoding the proteins were isolated. Additional cDNAs were isolated that encoded proteins approximately 90% identical with PR-2, PR-N, and PR-O. Although the proteins encoded by these cDNAs have not been identified, their deduced amino acid sequences have slightly basic or neutral calculated isoelectric points, as well as carboxy-terminal extensions. These physical characteristics are shared by the vacuolar form of beta-1,3-glucanase and other vacuolar localized analogs of PR proteins, suggesting that the unidentified proteins may be similarly localized. A preliminary evolutionary model that separates the beta-1,3-glucanase gene family from tobacco into at least five distinct subfamilies is proposed. The expression of beta-1,3-glucanase messenger RNAs (mRNAs) in response to infection by tobacco mosaic virus was examined. Messages for the acidic glucanases were induced similarly to the mRNAs for other PR proteins. However, the basic glucanase showed a different response, suggesting that different isoforms are differentially regulated by tobacco mosaic virus infection at the mRNA level.

Journal Article↗
PubMed1990

Structure of a tobacco endochitinase gene: evidence that different chitinase genes can arise by transposition of sequences encoding a cysteine-rich domain.

The endochitinases (E.C. 3.2.1.14, chitinase) are a structurally diverse group of enzymes believed to be important in the biochemical defense of plants against potential pathogens. The gene for a chitinase of Nicotiana tabacum L. cv. Havana 425 has been cloned and sequenced. The major transcription start is 11 bp upstream of the ATG codon and 28 bp downstream of the TATA box. The gene contains two introns and encodes a basic chitinase of 329 amino acids with a 23 amino acid N-terminal signal peptide followed by a 43 amino acid, cysteine-rich domain, which is linked by a hinge region to the main structure of the enzyme. This gene appears to be expressed because the exons are identical to the coding sequence of a cDNA which was isolated. Comparison of chitinase amino acid sequences from different plants indicates there are at least three classes of these enzymes: class I, basic chitinases with an N-terminal cysteine-rich domain and a highly conserved main structure; class II, chitinases similar to the main structure of class I chitinases but lacking the cysteine-rich domain; and, class III, chitinases with conserved sequences different from those of the class I and II enzymes. The sequences encoding the cysteine-rich domain in class I chitinases are flanked by 9-10 bp imperfect direct repeats suggesting that these domains arose from a common ancestral gene and were introduced into genes for class I enzymes by transposition events.

Amino Acid Sequence↗
PubMed1990

Evidence for a third structural class of beta-1,3-glucanase in tobacco.

Glucan endo-1,3-beta-glucosidases (beta-1,3-glucanases) have been implicated in several developmental processes and they may also play a direct role in the plant's defense against fungal pathogens. In an effort to characterize the glucanase gene family, complementary DNA clones encoding an acidic form of beta-1,3-glucanase have been isolated from tobacco. The cDNA was expressed in E. coli and shown to encode a beta-1,3-glucanase activity. The protein sequence encoded by the cDNA was found to match the partial protein sequence of PR-35, a previously characterized beta-1,3-glucanase. The protein encoded by the cDNA was purified from the extracellular fluid of TMV-infected tobacco leaves and found by immunological methods to correspond to glucanase PR-Q'. From a detailed analysis of the cDNA it is clear that this glucanase represents a third structural class of enzyme which differs substantially from both the basic, vacuolar glucanase and the acidic, extracellular forms (PR-2, PR-N and PR-O). It has previously been demonstrated that the basic form of beta-1,3-glucanase is synthesized as a pre-pro-enzyme and upon maturation the 21 amino acid signal peptide and a 22 amino acid carboxy-terminal peptide are removed. This processing event has been proposed to be involved with the vacuolar localization of the enzyme. By comparing the deduced protein structure of PR-Q' to that of the basic form it is evident that this extracellular enzyme is missing the carboxy-terminal 22 amino acids. The role of a conserved phenylalanine-glycine dipeptide in the processing of glucanases and other pathogenesis-related proteins from tobacco is discussed.

Amino Acid Sequence↗
PubMed1990

Isolation of complementary DNA clones encoding pathogenesis-related proteins P and Q, two acidic chitinases from tobacco.

Complementary DNA clones encoding two isoforms of the acidic endochitinase (chitinase, EC 3.2.1.14) from tobacco were isolated. Comparison of amino acid sequences deduced from the cDNA clones and the sequence of peptides derived from purified proteins show that these clones encode the pathogenesis-related proteins PR-P and PR-Q. The cDNA inserts were not homologous to either the bacterial form of chitinase or the form from cucumber but shared significant homology to the basic form of chitinase from tobacco and bean. The acidic isoforms of tobacco chitinase did not contain the amino-terminal, cysteine-rich "hevein" domain found in the basic isoforms, indicating that this domain, which binds chitin, is not essential for chitinolytic activity. The accumulation of mRNA for the pathogenesis-related proteins PR-1, PR-R, PR-P, and PR-Q in Xanthi.nc tobacco leaves following infection with tobacco mosaic virus was measured by primer extension. The results indicate that the induction of these proteins during the local necrotic lesion response to the virus is coordinated at the mRNA level.

Amino Acid Sequence↗
PubMed1988

Evidence for N- and C-terminal processing of a plant defense-related enzyme: Primary structure of tobacco prepro-beta-1,3-glucanase.

Tobacco glucan endo-1,3-beta-glucosidase (beta-1,3-glucanase; 1,3-beta-D-glucan glucanohydrolase; EC 3.2.1.39) exhibits complex hormonal and developmental regulation and is induced when plants are infected with pathogens. We determined the primary structure of this enzyme from the nucleotide sequence of five partial cDNA clones and the amino acid sequence of five peptides covering a total of 70 residues. beta-1,3-Glucanase is produced as a 359-residue preproenzyme with an N-terminal hydrophobic signal peptide of 21 residues and a C-terminal extension of 22 residues containing a putative N-glycosylation site. The results of pulse-chase experiments with tunicamycin provide evidence that the first step in processing is loss of the signal peptide and addition of an oligosaccharide side chain. The glycosylated intermediate is further processed with the loss of the oligosaccharide side chain and C-terminal extension to give the mature enzyme. Heterogeneity in the sequences of cDNA clones and of mature protein and in Southern blot analysis of restriction endonuclease fragments indicates that tobacco beta-1,3-glucanase is encoded by a small gene family. Two or three members of this family appear to have their evolutionary origin in each of the progenitors of tobacco, Nicotiana sylvestris and Nicotiana tomentosiformis.

Journal Article↗
PubMed1987

Regulation of a plant pathogenesis-related enzyme: Inhibition of chitinase and chitinase mRNA accumulation in cultured tobacco tissues by auxin and cytokinin.

Two endochitinases (EC 3.2.1.14) of M(r) values of approximately 34,000 and approximately 32,000 have been purified from cultured tissues of Nicotiana tabacum cv. Havana 425. The chitinase content of cloned tobacco pith tissues subcultured on hormone-free medium increases by approximately 5-fold to 8% of the soluble protein over a 7-day period. This induction is inhibited >90% by addition of combinations of the plant hormones auxin and cytokinin to the culture medium. Chitinase is also developmentally regulated in the intact plant. Not detectable in leaves near the top of the plant, it is 1-4% of the soluble protein in roots and lower leaves. A cDNA clone of tobacco chitinase was isolated containing a single, large open reading frame of 310 amino acids that includes the complete amino acid sequence of the mature enzyme. Chitinase and chitinase mRNA measured by RNA blot analysis show similar patterns of regulation indicating that chitinase accumulation is controlled, at least in part, at the mRNA level. The patterns were also similar to those obtained with glucan endo-1,3-beta-glucosidase (EC 3.2.1.39) suggesting that the two enzymes are coordinately regulated.

Journal Article↗
PubMed1986

A cytokinin mutant derived from cultured tobacco cells.

Tissues cultured from the leaf lamina of wild-type Nicotiana tabacum L. cv. "Havana 425" plants require an exogenous source of cytokinin for rapid growth. In contrast, leaf tissues of plants heterozygous or homozygous for the partially dominant, monogenic habituated leaf (H1-1) trait, exhibit a cytokinin-autotrophic phenotype in culture. Here we show that the H1 trait can arise in culture. Cytokinin autotrophic variants were obtained by culturing wild-type tissues of leaf lamina successively on media containing reduced concentrations of the cytokinin, kinetin. Plants regenerated from clones of these variants exhibited the H1 phenotype, which segregated in breeding tests as expected for a dominant, monogenic trait. This trait, designated H1-2, is inherited at a different locus than the H1-1 trait described earlier. Our results show that cytokinin mutants can arise in cell culture and that at least two genes regulate the cytokinin requirement of cultured tobacco tissues.

Cell Division↗
PubMed1986

Evidence for a cellular gene with potential oncogenic activity in plants.

During tumor inception in crown gall disease, a portion of the tumor-inducing (Ti) plasmid, the transferred DNA (T-DNA), is integrated into the genome of the plant cell. Autonomous growth of the transformants requires expression of genes in the tmr and tms regions of the T-DNA, which code for enzymes concerned with biosynthesis of the plant growth hormones cytokinin and auxin, respectively. We show that a mutation of the Habituated leaf gene, Hl, of tobacco can compensate for a defective tmr locus in expression of the tumor phenotype. This provides evidence that a specific host-cell gene has an oncogenic function similar to tmr in the T-DNA.

Cell Cycle↗
PubMed1986

Transdetermination of plant cells.

Tissues derived from the leaf lamina of Nicotiana tabacum L. cv. Havana 425 plants require cytokinin for continuous proliferation in culture, whereas tissues derived from the cortex of the stem are cytokinin autotrophic. Both phenotypes persist when the two types of cells are cloned, indicating that leaf- and cortex-derived cells are determined to express different cytokinin requirements in culture. We showed that cultures derived from leaf and cortex tissues of plants regenerated from cloned leaf and cortex cells exhibit the cytokinin requirement of comparable tissues of seed-grown plants. This provides direct evidence that plant cells can undergo transdetermination and that this process has an epigenetic basis.

Cell Differentiation↗
PubMed1986

Stability of the determined state.

During development parts of plants become determined for specific fates which can persist in populations of dividing cells. Students of plant development have tended to favour the view that the determined state is stabilized at the supracellular level. We provide evidence for the alternative view that determination can be inherited at the cellular level. This conclusion is based on the observation that cultured cells derived from the leaf lamina and cortex of the stem of tobacco plants inherit different states of cytokinin requirement. Plant regeneration experiments show that the cytokinin-requiring (C-) state characteristic of leaf cells and the cytokinin autotrophic (C+) state characteristic of cortex cells are stable but not permanent. Progeny of both cell types can give rise to complete plants with tissues exhibiting the cytokinin requirement of comparable tissues of seed grown plants. Pith cells can shift from the C- to the C+ state by a process known as habituation. Evidence is presented that this epigenetic change is stabilized by a positive-feedback mechanism in which cytokinins appear to promote their own biosynthesis. A single dominant, Mendelian gene, H1-2, controls expression of the C- and C+ phenotypes. There are hints that this gene changes state in cultured cells at rates expected for epigenetic modifications. This suggests that the C- and C+ state can also be stabilized by genetic mechanisms.

Cytokinins↗
PubMed1985

Hormonal regulation of beta1,3-glucanase messenger RNA levels in cultured tobacco tissues.

We describe the isolation of a cDNA clone of beta1,3-glucanase mRNA from Nicotiana tabacum L. cv. ;Havana 425' and its use to measure the kinetics of mRNA accumulation in cultured tobacco tissues treated with the plant hormones auxin and cytokinin. Northern blot analysis showed that the tissues contain a single 1.6 kb-sized beta1,3-glucanase mRNA. The levels of beta1,3-glucanase and beta1,3-glucanase mRNA increase by up to seven- and 20-fold, respectively, over a 7-day period in tissues subcultured on hormone-free medium and medium containing auxin or cytokinin added separately. Over the same interval of time, the content of both the enzyme and its mRNA remains at a constant low level in tissues subcultured on medium containing both auxin and cytokinin. The results show that auxin and cytokinin block beta1,3-glucanase production at the level of the mRNA.

Journal Article↗
PubMed1985

Reversible, cell-heritable changes during the development of tobacco pith tissues.

Cytokinin requiring cells of Nicotiana tabacum L. cv "Havana 425" can be induced in culture to become cytokinin autotrophic. This process is known as cytokinin habituation. Earlier we showed that pith parenchyma tissue consists of inducible cells, which habituate at high rates when treated with cytokinin, and noninducible cells, which remain cytokinin requiring under these conditions. The inducible and noninducible phenotypes are determined states that arise during the development of the tobacco plant and are inherited by individual cells. Here we show that pith tissue of plants regenerated from cloned lines of noninducible cells exhibits the inducible phenotype indicating that noninducible cells, or their descendants, can become inducible. This change in competence for habituation appears to have an epigenetic basis; it is reversible, occurs at high rates, and depends on the developmental state of the cells. The habituated state occurs in two forms that can be distinguished by their difference in developmental potential. Habituated cells derived from inducible pith cells give rise to normal plants whose leaf and pith tissues require cytokinin for growth in culture. In contrast, habituated cells obtained by transferring noninducible cells on media with progressively lower cytokinin concentrations give rise to plants whose leaf and pith tissues exhibit a cytokinin-habituated phenotype in culture.

Cell Line↗
PubMed1984

Concentration Gradients of trans-Zeatin Riboside and trans-Zeatin in the Maize Stem: Measurement by a Specific Enzyme Immunoassay.

A sensitive, specific enzyme immunoassay (EIA) for trans-zeatin riboside (ZR) and trans-zeatin (Z) in the 0.3 to 30 picomole range has been described. The reliability of the method for measuring ZR + Z in partially purified extracts of Zea mays L. tissues was verified by highperformance liquid chromatography. EIA measurements showed that there was a concentration gradient of ZR + Z along the length of the Zea stem. The topmost internodes, internodes 7 and 8 counting from the coleoptilar node, had the highest concentration ( approximately 130 picomoles per gram fresh weight). Moving basipetally, the concentration dropped approximately 10-fold to a minimum at internode 4, and then increased slightly in internodes 2 and 3. There were also gradients within each internode. The five lowest internodes contained the highest concentrations toward their apical end, the region which included the node; this asymmetry was less pronounced near the top of the plant.

Journal Article↗
PubMed1982

The relationship of indole-3-acetic acid content and growth of crown-gall tumor tissues of tobacco in culture.

We have measured the content of the auxin, indole-3-acetic acid (IAA), in cloned, crown-gall teratoma line of Nicotiana tabacum L. cv. "Turkish" by a highly specific and sensitive radioimmunoassay. This tissue line, which does not require auxin for continuous growth in culture, exhibits two phases of growth. During the first phase, which lasts about two weeks after subculturing, growth is exponential on a fresh weight basis and the content of IAA is about 10-7-10-6 mol.kg-1, but variable. During the second phase, growth rate declines gradually and the IAA content of the tissue drops dramatically; however, this drop does not result from a net loss of auxin by the tissue. The rate of growth during the exponential phase was not correlated with the IAA content of the tissue, but was strongly correlated with the IAA content of the inoculum. We found that rapidly growing leaves of Turkish tobacco have roughly the same IAA content as cultured teratoma tissues. Moreover, both tissues exhibited a similar relationships between auxin content expressed per leaf or per tissue explant and growth. These findings do not support the hypothesis that the autonomous growth of plant tumors results from an abnormally high content of auxin in the tissue.

Cell Division↗