Research Luc Roef

Abstract

This project envisages identifying components of the signal transduction cascades during oxidative stress in plants by means of an integrated immunological and proteomic approach. During its development a plant is continuously exposed to various kinds of stress. Its ability to react to these changes in a fast and appropriate manner is essential for its survival. Very often, changes in hormone homeostasis play an important role. Our knowledge regarding the role of plant growth regulators such abscisic acid (ABA), ethylene, jasmonic acid (JA) and salicylic acid (SA) as important signal molecules in stress responses is already substantial. Stress induced auxin and cytokinin action has been described in a restricted set of stress phenomena. Various studies point to oxidative stress as a central component in many cellular responses (Desikan et al., 2001; Neill et al., 2002). Oxidative stress results from an imbalance in the production and metabolism of reactive oxygen species (ROS). ROS are produced as a response to exposure to biotic and abiotic stress and act as a signal that triggers a variety of molecular, biochemical and physiological events. Nitrogen monoxide (NO) is very often an important component in the underlying signal transduction cascades. NO, a gaseous free radical, can interact with ROS in a number of ways and as such influences the response to biotic and abiotic stress factors (Delledonne et al., 1998; Neill et al., 2002; Neill et al., 2003). As is the case in animal models, cyclic GMP and cyclic ADPR are put forward as signal molecules in the plant NO signal transduction system. Cyclic GMP is produced in plants as a response to NO application (Pfeiffer et al., 1994) and in turn cADPR synthesis is thought to be induced by cGMP. Both have been shown to mimic certain functions of NO (Durner et al., 1998), and a specific inhibitor of guanylyl cyclase (ODQ) inhibits Arabidopsis thaliana NO-induced cell death. A membrane permeable cGMP-analog, 8-Br-cGMP, eliminates this inhibitory effect (Clarke et al., 2000). In animal systems, stress induced cADPR synthesis is activated via cGMP-dependent protein kinase. Until now, the existence of such a protein in higher plants has not been reported yet. The recent isolation of the gene for a putative cyclic nucleotide dependent protein kinase in our lab is a convincing candidate for this function. In its promoter region a considerable number of stress-regulated elements are found, such as the ABA-response element (ABRE), the "heat shock"-response element, the ABRE related "GC-repeat" (Litis et al., 1992) and the cold and water stress regulated dehydration (DRE)/"C-repeat"-response elements (Baker et al., 1994). The additional presence of a salicylic acid regulated promoter element (TCA), a wound induced response element, (WUN) (Pastuglia et al., 1997), and of the "TC-rich repeat", a stress and defence induced response element (Klotz en Lagrimini 1996), strengthens our proposition for a stress related function of this putative cyclic nucleotide dependent protein kinase.

Researcher(s)

• Promoter: Prinsen Els
• Promoter: Van Onckelen Harry
• Co-promoter: Laukens Kris
• Co-promoter: Roef Luc
• Co-promoter: Witters Erwin

Research team(s)

• Integrated Molecular Plant Physiology Research (IMPRES)

Project type(s)

• Research Project

Abstract

Several clues exist for the involvement of the NO-cGMP-cADPR transduction pathway in responses to stress conditions in plants. This transduction pathway is possibly analogous to the one already known in animals. A proper characterisation of the mechanism by which the cyclic GMP signal activates a cyclic ADPR signal is currently missing for plants. For several years now, the laboratory for plant biochemistry and physiology of the university of Antwerpen has been researching cyclic nucleotides in plants. During the course of this research it was shown that Nicotiana tabacum 'BY-2' cells and Arabidopsis thaliana express a putative cyclic nucleotide dependent protein kinase/phosphatase gene. Based on sequence homology we expect the encoded protein to contain a domain resembling protein phosphatase 2C, followed by a cyclic nucleotide binding domain and a catalytical kinase domain (=> PP2C-PKNR-PKNC). This is a surprising digression from the prototypical cyclic nucleotide dependent protein kinases as they are known in yeasts or animals. Several alternative transcripts appear and preliminary data seem to indicate a fluctuation during the cell cycle. An analysis of the putative promoter regions of this gene showed several response elements regulated not only by the cell cycle, but by light and stress as well. The aim of this project is to determine the relation of this protein to the elements of the proposed NO-cGMP-cADRP transduction pathway, based on the previously described observations. To achieve this we plan to use plants (Arabidopsis en BY-2) available to us in the lab, in which (several variant forms) of the protein are either over-expressed or knocked-out. Plants (Arabidopsis en BY-2) containing promoter-EGFP-GUS constructs will be used as well. These organisms, both wild-type and transformant, will be subjected to different kinds of biotic and abiotic stress and the different signalling molecules (NO, cGMP, cADPR) will be individually administered to them. Each time the signalling molecules will be observed using biochemical, microscopical and proteomics techniques. Observation of differences in these molecules and morphological differences between wild-type and mutant plants, with the knocked-out or the constitutively activated gene, should provide us with indications about the functioning of the gene in the proposed transduction pathway.

Researcher(s)

• Promoter: Van Onckelen Harry
• Co-promoter: Roef Luc
• Fellow: Van Ingelgem Carl

Research team(s)

• Integrated Molecular Plant Physiology Research (IMPRES)

Project type(s)

• Research Project

Abstract

The project aims at establishing the biochemical properties and physiological role of a number of splice variants of a totally new putative hybrid cyclic nucleotide dependent protein kninase/phosphatase from higher plants by means of a combination of state of the art methods in genetic analysis and proteome analysis. A focus is put on a presumed role in the regulation of the plant cell cycle.

Researcher(s)

• Promoter: Roef Luc

Research team(s)

• Integrated Molecular Plant Physiology Research (IMPRES)

Project type(s)

• Research Project

Abstract

The purpose of the research consists of the clarification of the cAMP metabolism in higher plants. Therefore, cAMP content and adenylate cyclase activity are being measured in (transformed) higher plant tissues. Furthermore, we try to find the genetical background of the cAMP metabolism by means of molecular biological techniques

Researcher(s)

• Promoter: Van Onckelen Harry
• Fellow: Roef Luc

Research team(s)

Project type(s)

• Research Project

Abstract

The purpose of the research consists of the clarification of the cAMP metabolism in higher plants. Therefore, cAMP content and adenylate cyclase activity are being measured in (transformed) higher plant tissues. Furthermore, we try to find the genetical background of the cAMP metabolism by means of molecular biological techniques

Researcher(s)

• Promoter: Van Onckelen Harry
• Fellow: Roef Luc

Research team(s)

Project type(s)

• Research Project

Abstract

Researcher(s)

• Promoter: Van Onckelen Harry
• Fellow: Roef Luc

Research team(s)

Project type(s)

• Research Project