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Van Montagu M

Publications and source records attributed to Van Montagu M.

7 recordsLinked to original sources
PubMed2000

Cloning and molecular analysis of two new sesquiterpene cyclases from Artemisia annua L.

Artemisia annua L. is the only source of artemisinin, a new promising antimalarial drug (Qinghaosu Antimalarial Coordinating Research Group, Chin. Med. J. 92 (1979) 811). Our efforts are focused on the overproduction of this valuable medicine by genetic engineered A. annua plants. Therefore, we decided to isolate the gene(s) encoding sesquiterpene cyclase(s) in A. annua as a first step in improving artemisinin yield. Four partial genomic clones, gASC21, gASC22, gASC23 and gASC24, were isolated through polymerase chain reaction (PCR) with degenerated primers based on homologous boxes present in sesquiterpene cyclases from divergent sources. Intron-exon organisation of those partial genomic clones was analysed and it was shown that A. annua contains a gene family for sesquiterpene cyclases. Based on gASC21, gASC22, gASC23 and gASC24 sequences, the full-length cDNA clones cASC34 and cASC125 were subsequently isolated by rapid amplification of cDNA ends PCR. The derived amino acid sequences of both full-length clones show high homology with sesquiterpene cyclases from plants. Reverse transcription-PCR analysis revealed transient and tissue specific expression patterns for cASC34 and cASC125, in contrast to the constitutively expressed 8-epicedrol synthase, a previously reported sesquiterpene cyclase from A. annua. Both cASC34 and cASC125 could only be detected in flowering plants when artemisinin concentration is at highest.

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PubMed2000

The early years

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PubMed1999

Sequences throughout the basic beta-1,3-glucanase mRNA coding region are targets for homology dependent post-transcriptional gene silencing.

In the transgenic tobacco line T17, plants homozygous for the gn1 transgene display developmentally regulated post-transcriptional silencing of basic beta-1,3-glucanase genes. Previously, it has been shown that silencing involves a markedly increased turnover of silencing-target glucanase mRNAs. Using a two-component viral reporter system facilitated a comparison, in a quantitat- ive manner, of the relative silencing efficiencies of various sequences derived from the gn1 transgene. The results show that target sites for the silencing mechanism are present throughout the coding region of the gn1 mRNA. Similar-sized coding region sequences along the entire gn1 mRNA display a similar susceptibility to the silencing mechanism. The susceptibility to silencing increases as the coding region elements increase in size. Relative to internal sequences, the 5' and 3' terminal regions of the gn1 mRNA are inefficient targets for the silencing machinery. Importantly, sequences of the gn1 transgene that are not part of the mature gn1 mRNA are not recognized by the silencing machinery when expressed in chimeric viral RNAs. These results show that the glucanase silencing mechanism in T17 plants is primarily directed against gn1 mRNA-internal sequences and that terminal sequences of the gn1 mRNA are relatively unaffected by the silencing mechanism.

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PubMed1998

Ethylene-mediated phenotypic plasticity in root nodule development on Sesbania rostrata.

Leguminous plants in symbiosis with rhizobia form either indeterminate nodules with a persistent meristem or determinate nodules with a transient meristematic region. Sesbania rostrata was thought to possess determinate stem and root nodules. However, the nature of nodule development is hybrid, and the early stages resemble those of indeterminate nodules. Here we show that, depending on the environmental conditions, mature root nodules can be of the indeterminate type. In situ hybridizations with molecular markers for plant cell division, as well as the patterns of bacterial nod and nif gene expression, confirmed the indeterminate nature of 30-day-old functional root nodules. Experimental data provide evidence that the switch in nodule type is mediated by the plant hormone ethylene.

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PubMed1997

Cell proliferation and hair tip growth in the Arabidopsis root are under mechanistically different forms of redox control.

We provide evidence that the tripeptide thiol glutathione (GSH) participates in the regulation of cell division in the apical meristem of Arabidopsis roots. Exogenous application of micromolar concentrations of GSH raised the number of meristematic cells undergoing mitosis, while depletion of GSH had the opposite effect. A role for endogenous GSH in the control of cell proliferation is also provided by mapping of GSH levels in the root meristem using the GSH-specific dye monochlorobimane and confocal laser scanning microscopy. High levels of GSH were associated with the epidermal and cortical initials and markedly lower levels in the quiescent center. The mechanisms controlling cell division could also be triggered by other reducing agents: ascorbic acid and dithiothreitol. Our data also reveal significant plasticity in the relationship between the trichoblast cell length and the hair it subtends in response to alterations in intracellular redox homeostasis. While mechanisms that control trichoblast elongation are influenced by nonspecific redox couples, root hair tip growth has a more specific requirement for sulfhydryl groups. The responses we describe here may represent the extremes of redox control of root plasticity and would allow the root to maintain exploration of the soil under adverse conditions with minimal cell divisions and root hair production or capitalize on a favorable environment by production of numerous long hairs. Redox sensing of the environment and subsequent redox-dependent modulation of growth and development may be crucial components in the strategies plants have evolved for survival in a fluctuating environment.

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PubMed1997

Ethylene can stimulate Arabidopsis hypocotyl elongation in the light.

Ethylene inhibits hypocotyl elongation in etiolated Arabidopsis seedlings. However, when Arabidopsis was grown in the light in the presence of ethylene or its precursor 1-aminocyclopropane-1-carboxylic acid (ACC), a marked induction of hypocotyl elongation occurred. This resulted from an increase in cell expansion rather than cell division. The effects of ethylene and ACC were antagonized by the ethylene action inhibitor Ag+. The elongation response was absent or weakened in a set of ethylene-insensitive mutants (etr1-3, ein2-1, ein3-1, ein4, ain1-10, ein7). With the exception of ein4, the degree of inhibition of hypocotyl elongation was correlated with the strength of the ethylene-insensitive phenotype based on the triple response assay. In addition, the constitutive ethylene response mutant ctr1-1, grown in the light, had a longer hypocotyl than the wild type. Exogenous auxin also induced hypocotyl elongation in light-grown Arabidopsis. Again, the response was abolished by treatment with Ag+, suggesting that ethylene might be a mediator. The results showed that, depending on light conditions, ethylene can induce opposite effects on cell expansion in Arabidopsis hypocotyls.

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