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Johan Memelink

Publications and source records attributed to Johan Memelink.

9 recordsLinked to original sources
PubMed2005

The use of genetics to dissect plant secondary pathways.

Plant secondary metabolism comprises an enormous diversity in compounds and enzymes, and wide spectra of mechanisms of gene regulation and of transport of metabolites and enzymes. Genetic approaches using the model plant Arabidopsis thaliana have contributed importantly to recent progress in understanding glucosinolate biosynthesis and its intricate linkage with auxin homeostasis. Arabidopsis genetics have also caused revolutionary changes in the existing views on the metabolic intermediates and enzyme activities that are involved in phenylpropanoid biosynthesis. Some progress has been achieved in understanding the transcriptional regulation of the flavonoid pathway. Transcriptional regulators have also been identified for glucosinolate and terpenoid indole alkaloid biosynthesis.

Gene Expression Regulation, Plant↗
PubMed2005

Tailoring the plant metabolome without a loose stitch.

Metabolic engineering holds great promise as a technique for improving crop plants. However, introducing new metabolic steps can disturb normal metabolism and gene expression, affecting phenotype and quality in undesired ways. Recently, Charlotte Kristensen et al. reported that introducing the sorghum pathway for biosynthesis of the cyanogenic glucoside dhurrin into Arabidopsis plants resulted in high dhurrin levels and only marginal side effects on the metabolome and the transcriptome.

Arabidopsis↗
PubMed2004

Zinc finger proteins act as transcriptional repressors of alkaloid biosynthesis genes in Catharanthus roseus.

In Catharanthus roseus cell suspensions, the expression of several terpenoid indole alkaloid biosynthetic genes, including two genes encoding strictosidine synthase (STR) and tryptophan decarboxylase (TDC), is coordinately induced by fungal elicitors such as yeast extract. To identify molecular mechanisms regulating the expression of these genes, a yeast one-hybrid screening was performed with an elicitor-responsive part of the TDC promoter. This screening identified three members of the Cys(2)/His(2)-type (transcription factor IIIA-type) zinc finger protein family from C. roseus, ZCT1, ZCT2, and ZCT3. These proteins bind in a sequence-specific manner to the TDC and STR promoters in vitro and repress the activity of these promoters in trans-activation assays. In addition, the ZCT proteins can repress the activating activity of APETALA2/ethylene response-factor domain transcription factors, the ORCAs, on the STR promoter. The expression of the ZCT genes is rapidly induced by yeast extract and methyljasmonate. These results suggest that the ZCT proteins act as repressors in the regulation of elicitor-induced secondary metabolism in C. roseus.

Alkaloids↗
PubMed2004

Activation of the oxidative burst by yeast elicitor in Catharanthus roseus cells occurs independently of the activation of genes involved in alkaloid biosynthesis.

In Catharanthus roseus cell suspensions, expression of several terpenoid indole alkaloid (TIA) biosynthetic genes, including those encoding strictosidine synthase and tryptophan decarboxylase, is coordinately induced by fungal elicitors such as yeast extract (YE). This induction is mediated by several signaling steps including the biosynthesis of jasmonic acid, and the activation of the jasmonic acid-responsive ORCA transcription factors. We investigated a possible role of reactive oxygen species (ROS) as a second messenger in this system. YE was shown to activate the production of ROS, which was dependent on protein phosphorylation and calcium influx. However, ROS generation was neither necessary for the induction of genes involved in TIA biosynthesis by YE nor by itself sufficient to induce these genes. Therefore, we conclude that activation of the oxidative burst by YE occurs independently of the activation of genes involved in TIA biosynthesis.

1,2-Dihydroxybenzene-3,5-Disulfonic Acid Disodium ↗
PubMed2003

CrMYC1, a Catharanthus roseus elicitor- and jasmonate-responsive bHLH transcription factor that binds the G-box element of the strictosidine synthase gene promoter.

A cDNA encoding a bHLH transcription factor was isolated by the yeast one-hybrid system from a Catharanthus roseus cDNA library using the G-box element of the Strictosidine synthase gene promoter as bait. The corresponding protein (named CrMYC1) was shown to bind specifically to the G-box in yeast. In C. roseus suspension cells CrMYC1 mRNA levels are induced by fungal elicitor and jasmonate suggesting that CrMYC1 may be involved in the regulation of gene expression in response to these signals.

Asteraceae↗
PubMed2003

T-DNA activation tagging.

T-DNA activation tagging is a method to generate dominant mutations in plants or plant cells by random insertion of a T-DNA carrying constitutive enhancer elements, which can cause transcriptional activation of flanking plant genes. The method consists of generating a large number of transformed plants or plant cells using a specialized T-DNA construct, followed by selection for the desired phenotype. Subsequently, the activated plant gene is rescued from selected mutant transformants for further functional analysis. Since the exact procedure depends on the plant material and the selected phenotype, this chapter describes one specific example of T-DNA activation tagging of suspension-cultured cells, including, where possible, cross-references to more general applications of the technique.

Arabidopsis↗
PubMed2002

Transcription factors controlling plant secondary metabolism: what regulates the regulators?

Plants produce secondary metabolites, among others, to protect themselves against microbial and herbivore attack or UV irradiation. Certain metabolite classes also function in beneficial interactions with other organisms. For example, anthocyanin pigments and terpenoid essential oils have key roles in attraction of flower pollinators. Secondary metabolites also have direct uses for man. Flavonoids and terpenoids for example have health-promoting activities as food ingredients, and several alkaloids have pharmacological activities. Controlled transcription of biosynthetic genes is one major mechanism regulating secondary metabolite production in plant cells. Several transcription factors involved in the regulation of metabolic pathway genes have been isolated and studied. There are indications that transcription factor activity itself is regulated by internal or external signals leading to controlled responses. The aim of this review is to discuss the regulation of transcription factors involved in secondary metabolism in plants at gene and protein levels, using phenylpropanoid and terpenoid indole alkaloid pathways as two well-studied examples.

Alkaloids↗
PubMed2002

Transcription factors: tools to engineer the production of pharmacologically active plant metabolites.

Plants produce a variety of secondary metabolites, some of which are used as pharmaceuticals or are health promoting as food components. Recent genetic studies on the flavonoid biosynthetic pathway show that transcription factors are efficient new molecular tools for plant metabolic engineering to increase the production of valuable compounds. The use of specific transcription factors would avoid the time-consuming step of acquiring knowledge about all enzymatic steps of a poorly characterized biosynthetic pathway. Although genetic approaches are difficult for most plant species, promoter studies of single-pathway genes and T-DNA activation tagging are feasible alternative approaches for isolating transcription factors, as illustrated for terpenoid indole alkaloid biosynthesis in Catharanthus roseus.

Alkaloids↗