Research Kris Vissenberg

Abstract

My study aims to elucidate the role of reactive oxygen species (ROS) in regulating cell wall (CW) biomechanics during plant growth, a missing link in the growth regulatory pathway. Understanding this process is crucial for various aspects of plant biology including plant-pathogen interactions and stress responses. The research intends to integrate ROS signaling with CW integrity pathways to provide a mechanistic framework which could underpin future fundamental and agricultural development. I will use fast-growing root hairs of Arabidopsis thaliana as plant cell model to (1) quantify subcellular ROS dynamics and uncover its link with CW biomechanics, (2) study CW-ROS feedback regulation, (3) reveal the spatio-temporal dynamics of protein interactions involved in ROS-CW growth pathways, and (4) identify the ligands of ERULUS, a receptor-like kinase involved in CW integrity sensing. Dedicated work packages will make use of several interdisciplinary approaches that are present in the host-lab or through collaborations. These include the development of pH-insensitive cell wall-targeted ROS reporters, generation of crosses of mutants and transgenic lines, molecular modeling, ligand identification and characterization, and multiparametric live cell imaging experiments coupled to microfluidics. Overall, the research aims to provide a comprehensive understanding of the ROS-CW growth pathway, which could have significant implications for plant biology and agriculture.

Researcher(s)

• Promoter: Vissenberg Kris
• Fellow: Meul Yentl

Research team(s)

• Integrated Molecular Plant Physiology Research (IMPRES)

Project type(s)

• Research Project

Abstract

During growth, plant cell walls are sufficiently strong to resist turgor pressure and avoid lysis, yet at the same time they need to be extensible for growth. To explain this dual functionality, we need to understand how cells perceive the rheological status of their cell walls and how they, in turn, adapt the wall growth capacities. The ENDOPOL project builds upon recent findings of both promotors' labs on root hairs, showing that a plasma membrane-localized receptor-complex (LLG-CrRLK1Ls), together with secreted Rapid Alkalinization Factors (RALF proteins) and Leucine-rich repeat extensin-like (LRX) proteins serve as 'cell wall integrity sensing module' and link cell wall status to cytoplasmic signalization fine-tuning wall rheology. Preliminary data suggests a controlling role of endocytosis in this process. Using state-of-the-art microscopy and molecular biology approaches we will reveal 1) the module member dynamics and localization towards each other at the submicron to nano-scale, and in relation to pectin organization, 2) how endocytosis is embedded and regulated within the cell wall integrity module, 3) RALF-perception with high spatial resolution, and 4) factors involved in downstream RALF-CrRLK1Ls signaling. This project combines the strengths of both labs and aims a mechanistic understanding of how the organization, interaction and dynamics of the involved proteins relate to the fast and nanoscale changes in cell wall/pectin status that control growth.

Researcher(s)

• Promoter: Vissenberg Kris

Research team(s)

• Integrated Molecular Plant Physiology Research (IMPRES)

Project type(s)

• Research Project

Abstract

Per- and polyfluoroalkyl substances (PFAS) are chemicals globally present in the environment and biota, as a result of their massive production and use in numerous applications, such as food contact paper, fire-fighting foams, textiles, construction and cleaning products. Their bioaccumulative and persistent properties have led to global regulatory measures for PFOS and PFOA. These are the most frequently detected legacy PFAS and their concentrations are still very high in the environment and biota. In addition, there are many emerging PFAS alternatives developed, with similar structures and chemical properties, not yet regulated and hence used unrestrictedly. However, very little or no information is available on the bioavailability, biomagnification and toxic effects of these emerging compounds, particularly for the terrestrial environment. PFAS may thus accumulate in the environment, posing risks to organisms. There are also many uncertainties on which factors might influence the bioavailability and biomagnification, especially of emerging PFAS. The identification of emerging PFAS, which have largely replaced the legacy PFAS, would allow us to investigate the environmental relevance of currently-used PFAS, as well as to characterize possible point sources. Detailed field studies on soil, plants, invertebrates (e.g. earthworms, woodlice, caterpillars, snails, slugs, and spiders), and great tits (Parus major; a songbird model species) planned in this project will provide us with: 1) an overview of the distribution of legacy and emerging PFAS present in the terrestrial environment near a fluorochemical polluting hotspot in Antwerp, 2) how the concentrations in the food chain are influenced by soil properties, and 3) their potential toxicity in key model species. In addition, experimental lab studies with PFAS and elevated temperature (T) as stressors on terrestrial invertebrates and plants will be performed to: 4) disentangle causal links from confounding effects regarding the soil properties, 5) verify whether or not increased T and PFAS have an additive toxic effect when combined, and 6) create a mechanistic framework explaining the underlying subcellular basis of root growth responses towards PFAS/increased T in the plant model species Arabidopsis thaliana. This project will allow us to understand the bioavailability and mechanism of the toxicity of emerging and legacy PFAS in plants, invertebrates, and birds and will offer instruments for regulators to assess the environmental risk and potential effects on human health.

Researcher(s)

• Promoter: Bervoets Lieven
• Co-promoter: Covaci Adrian
• Co-promoter: Eens Marcel
• Co-promoter: Prinsen Els
• Co-promoter: Vissenberg Kris

Research team(s)

• Ecosphere

Project type(s)

• Research Project

Abstract

At the Department of Biology at the University of Antwerp, techniques for detailed monitoring of Arabidopsis thaliana root hair development and detection of their growth, have been refined and made available for the study of regulatory pathways and mechanisms. These techniques include the optimized growth of Arabidopsis thaliana plants for high quality root hair development, the use of confocal microscopy for detection of fluorescent fusion proteins in localization studies, and a procedure for quantifying the external pH oscillations of root hairs. Together, these techniques can reveal possible up or down regulation of the plasma membrane H+-ATPases (AHAs), that are essential for maintaining an electrochemical gradient of protons in plant cells, that in turn drives secondary active transport processes across cell membranes. In this specific collaboration, these techniques are applied for phenotyping of root hairs of AHA and ERULUS receptor kinase mutants relative to wild type plants. Also, the root hair localization of the AHA2 and AHA7 mutant pumps are examined.

Researcher(s)

• Promoter: Vissenberg Kris

Research team(s)

• Integrated Molecular Plant Physiology Research (IMPRES)

Project type(s)

• Research Project

Abstract

Crucial insights in cell and developmental biology have been gained by virtue of live cell imaging technology. Along with a growing complexity of cellular models and the finesse with which they can be genetically engineered, comes a demand for more advanced microscopy. In brief, modern comprehensive cell systems research (cellomics) requires light-efficient, intelligent and interactive imaging modalities. To address this shared need, our consortium has identified a state-of-the art platform that allows ultrafast, yet minimally invasive imaging of small to medium-sized biological samples (from single cells to organoids) at high resolution, so as to capture dynamic events that range in timescale from voltage fluctuations to successive cell divisions. To only focus on those events that are truly of interest, and thereby boost throughput, the system is equipped with online image recognition capabilities. Finally, to allow targeted perturbations such as local damage induction or optogenetic switching, small regions can be selectively illuminated in the field of view. With this level of control, it will become possible to interrogate (sub-)cellular processes with unprecedented detail. The platform readily finds applications in diverse frontline research fields including neuroscience, cardiovascular research and infectious diseases, rendering it an indispensable asset for the applicants, the microscopy core facility and the University of Antwerp.

Researcher(s)

• Promoter: De Vos Winnok
• Co-promoter: Caljon Guy
• Co-promoter: De Meyer Guido
• Co-promoter: Jordanova Albena
• Co-promoter: Rademakers Rosa
• Co-promoter: Timmerman Vincent
• Co-promoter: Timmermans Jean-Pierre
• Co-promoter: Vissenberg Kris
• Co-promoter: Weckhuysen Sarah

Research team(s)

• Laboratory of cell biology and histology

Project type(s)

• Research Project

Abstract

Plants grow towards areas favourable for their survival. This is the result of individual cell growth. The latter can only occur when the cell wall, which surrounds plant cells, is not too stiff, yet not too loose. This requires constant monitoring of cell wall biomechanics. How cells sense and control cell wall biomechanics during growth is the central theme of this project. Plants have evolved proteins to monitor and respond to changes in cell wall properties. Members of the 'Catharanthus roseus Receptor-Like kinases 1-Like' (CrRLK1L) protein family serve as cell wall composition sensors during cell growth. In Arabidopsis t. we identified the CrRLK1L ERULUS (ERU), which controls cell wall composition and pectin (cell wall component that controls flexibility) dynamics during root hair growth, presumably together with FERONIA (FER), another CrRLK1L. To understand how cell wall biomechanics are regulated during cell growth we will study (1) the relation between pectin modification and root hair growth, (2) the cell wall properties of ERU and FER mutants, (3) which signals are perceived by ERU and FER, and (4) the functional relation between cell wall pH, pectin, RALFs (cell wall localized small peptide CrRLK1L ligands), Ca2+, ERU and FER signaling in regulating cell growth. Our results will provide an integrated view on the processes that control cell wall biomechanics during cell growth, using ERU and FER root hair growth as a model.

Researcher(s)

• Promoter: Vissenberg Kris
• Fellow: Schoenaers Sébastjen

Research team(s)

• Integrated Molecular Plant Physiology Research (IMPRES)

Project type(s)

• Research Project

Abstract

The main function of plant roots is to forage for soil resources. Root hairs, tubular extensions of the root's outer cell layer, represent 70% of the root surface area and are the primary site of water and nutrient uptake. When grown in specific soil conditions, mutants with shorter root hairs have reduced plant fitness. Understanding how factors like the plant hormone auxin control root hair development are therefore critical to optimise agricultural systems with respect to water and fertilizer use. The data are disjointed and an integrated view is lacking. We will use the model plant Arabidopsis and our recently published mutant that grows shorter root hairs. The expression of the mutated gene, ERULUS, is directly controlled by auxin and normally encodes a kinase, a protein that regulates its targets' activity by phosphorylation. Changes in specific cell wall enzyme activity, modifying pectins, causes strongly reduced root hair growth in the mutant. Our aim is to elucidate the pathway that starts from auxin, involves ERULUS and cell wall metabolism and results in normal root hairs. We identified 3 objectives that concentrate on different levels: i) Unravelling the control of ERU expression by auxin ii) Characterization of ERU protein functionality iii) Elucidation of ERU-mediated control of root hair growth through specific cell wall enzymes The data gathered during these 3 work packages will allow me to interconnect pathways up- and downstream of the identified ERULUS kinase and it will probe auxin regulation throughout the root hair expansion network.

Researcher(s)

• Promoter: Vissenberg Kris
• Fellow: Claeijs Naomi

Research team(s)

• Integrated Molecular Plant Physiology Research (IMPRES)

Project type(s)

• Research Project

Abstract

Metal contamination is a major environmental concern in many industrialized and developing countries since metals enrich in the food chain, creating threats for human and animal health. Metal-risk assessments in soil are mostly based on the effects of single metals, while contaminated soils are frequently characterized by multi-metal contaminations. Even though metals may cause no or very limited observable effects when applied individually, the combination of different chemicals can produce significant toxic effects. There is thus an increased need to understand how metals act together in mixtures and how these should be handled in regulatory risk assessment. Plant toxicity tests mainly use 1 metal and assess general endpoints and often do not provide any insight into the effect on the underlying biological processes that lead to the observed effects, making comparison of the effects of different metals, supplied as singles or mixtures, difficult. We will use Arabidopsis as model plant to perform analysis of the effects of Cd, Cu and Zn at the transcriptome, proteome, metabolome and cellular physiology level using state of the art technology. This systems biology approach will allow us to integrate the data obtained at the different organisation levels of the root and to create a series of events in order to explain the observed effect of metal addition on Arabidopsis root growth. This formation of an 'adverse outcome pathway', used for animal systems, is novel for plants.

Researcher(s)

• Promoter: Vissenberg Kris
• Co-promoter: Blust Ronny
• Fellow: Kranchev Mario

Research team(s)

• Integrated Molecular Plant Physiology Research (IMPRES)

Project type(s)

• Research Project

Abstract

The application concerns an innovative microscopy platform for visualizing cells, tissue specimen and living small model organisms in three dimensions at unprecedented speed and with excellent resolution and contrast. As a unique feature, the platform is equipped with a light-sheet module, which is based on an orthogonal configuration of laser-generated, micrometer-thin plane illumination and sensitive one-shot detection. Seamless integration with confocal modalities enables imaging the same sample from the micro- to the mesoscale. The device has a broad application radius in the neurosciences domain inter alia for studying neurodegeneration and -regeneration (e.g. whole brain imaging, optogenetics); but it also has direct utility in various other fields such as cardiovascular research (e.g. plaque formation and stability), plant developmental research (e.g. protein localization during plant growth) and ecotoxicology (e.g. teratogenicity and developmental defects in zebrafish). Furthermore, its modular construction will enable adaptation and targeted expansion for future imaging needs.

Researcher(s)

• Promoter: Timmermans Jean-Pierre
• Co-promoter: Adriaensen Dirk
• Co-promoter: De Meyer Guido
• Co-promoter: De Vos Winnok
• Co-promoter: D'Haese Patrick
• Co-promoter: Giugliano Michele
• Co-promoter: Jordanova Albena
• Co-promoter: Keliris Georgios A.
• Co-promoter: Knapen Dries
• Co-promoter: Maudsley Stuart
• Co-promoter: Ponsaerts Peter
• Co-promoter: Timmerman Vincent
• Co-promoter: Vissenberg Kris

Research team(s)

• Laboratory of cell biology and histology

Project type(s)

• Research Project

Abstract

This project aims to increase our knowledge on the regulation of plant cell elongation, as it shapes plant size and form and determines primary biomass production. Arabidopsis thaliana will serve as model plant and the hypocotyl will be used to identify key-players in the regulation of (cell) elongation. The hypocotyl's elongation is very prominent in the dark, but upon perception of light, elongation is rapidly inhibited. We have identified and phenotyped a unique mutant, apollo, that fails to inhibit elongation in the light, but that shows all other signs of de-etiolation. In order to identify genes and miRNAs with a crucial role in the light-regulation of cell elongation we will compare the transcriptome of 1) dark-grown wild-type with dark-grown apollo, 2) light-grown wild-type with light-grown apollo and 3) dark-grown wild-type but transfered to light with dark- grown apollo but also transfered to light using Next Generation Sequencing (NGS). In addition, the mutant results in the sustained up-regulation of a transcription factor (ORPHEUS) that in wild-type seedlings is down-regulated upon light preception, identifying it as a potential switch to regulate expansion and inhibition of expansion. Therefore, we will identify the target genes of this transcription factor using NGS on DNA that results from chromatin immunoprecipitation. A functional analysis with a reverse genetic approach will link the individual genes to their function and role in the expansion-regulation.

Researcher(s)

• Promoter: Vissenberg Kris

Research team(s)

• Integrated Molecular Plant Physiology Research (IMPRES)

Project type(s)

• Research Project

Abstract

This project aims to increase our knowledge on the regulation of plant cell elongation, as it shapes the size and form of plants and plays a key-role in the primary production of biomass. The elongation of the dark-grown Arabidopsis hypocotyl occurs only through cell elongation, making the hypocotyl an ideal model to study (regulation of) cell elongation. One of the prerequisites for this etiolated growth is the deposition of a thick cell wall during the slow growth phase, which becomes extensively remodelled and thinned during expansion. Furthermore, hypocotyl elongation is rapidly inhibited when light is perceived.

Researcher(s)

• Promoter: Vissenberg Kris

Research team(s)

• Integrated Molecular Plant Physiology Research (IMPRES)

Project type(s)

• Research Project

Abstract

Two kinases and one kinase-interacting protein were identified using 2 microarray datasets of root hair mutants coupled to a comprehensive reverse genetics approach. The project aims to reveal how they are regulated by auxin and how they regulate tip-growth in root hairs. This can be summaried by the following objectives: 1) The genes are auxin-regulated in an auxin response factor-dependent manner (ARF7/ARF19). Chromatin ImmunoPrecipitation (ChIP) followed by gene-specific PCRs will reveal whether they are direct or indirect targets of these ARFs (Dr. Hill, Nottingham Univ.) and qPCR will quantify their expression levels in several auxin-signaling mutants, further unraveling their auxin-regulation. 2) The involvement of the genes in NADPH oxidase-dependent, auxin-regulated ROS accumulation in root hairs will be monitored. This study involves molecular biological techniques and different forms of microscopy. 3) With the use of ion-specific vibrating probes and ion-sensitive dyes coupled to ratio-imaging, the effect of the gene knock-outs on extracellular ion-fluxes and intracellular ion-gradients at the growing tip root hairs - a conditio sine qua non for sustaining tip-growth - will be quantified (Prof. Feijó, Lisbon Univ.). 4) The interaction partners/targets of the proteins will be identified using tandem affinity purification (Dr. De Jaeger, Gent), followed by kinase assays. T-DNA insertion lines for the identified interaction partners will be screened for root hair (and pollen tube growth) phenotypes. Together, these objectives will clarify how auxin regulates these genes and how these genes, in turn, regulate tipgrowth in root hairs (and pollen tubes)/

Researcher(s)

• Promoter: Vissenberg Kris
• Fellow: Schoenaers Sébastjen

Research team(s)

• Integrated Molecular Plant Physiology Research (IMPRES)

Project type(s)

• Research Project

Abstract

Hormone action was until recently mainly viewed as an organ-specific process. Based on recent findings for auxins, gibberellins and brassinosteroids, we speculate that cell type specificity plays a general role in hormone action mechanisms. In this project, cell type specificity of ethylene action will be addressed by using cell type specific promoters driving EBF1 and EBF2 (EIN3 binding F-box 1 and 2), two regulators of the prevalence of the EIN3/EIL1 proteins, positive regulators of ethylene signaling.

Researcher(s)

• Promoter: Vissenberg Kris

Research team(s)

• Integrated Molecular Plant Physiology Research (IMPRES)

Project type(s)

• Research Project

Abstract

Based on the transcriptome data the project aims to generate a gene regulatory network leading to root bending and to unravel the role and function of several of the identified genes in the bending response. This will be achieved by in silico analysis of the available data and a detailed analysis of the expression pattern, of the effect of gene-overexpression, of the location of the gene product and possible interaction partners.

Researcher(s)

• Promoter: Vissenberg Kris

Research team(s)

• Integrated Molecular Plant Physiology Research (IMPRES)

Project type(s)

• Research Project

Abstract

Developmental processes involve a complex network of interactions between multiple regulatory processes that traditionally are studied separately. We propose a systems biology approach, whereby experimental biologists closely interact with mathematical modellers, to unravel the functional relationships between auxin signalling, cell division and expansion and whole leaf morphogenesis.

Researcher(s)

• Promoter: Beemster Gerrit
• Co-promoter: Broeckhove Jan
• Co-promoter: Prinsen Els
• Co-promoter: Vanroose Wim
• Co-promoter: Vissenberg Kris

Research team(s)

• Integrated Molecular Plant Physiology Research (IMPRES)

Project type(s)

• Research Project

Abstract

Based on at least 5 separate micro-array studies many genes differentially expressed between a control and a mutant/ treated organ/different time point were identified. In a first step available T-DNA knock-out or knockdown lines were analysed and those with a growth phenotype were selected for further detailed study. This involves a) spatiotemporal gene expression analysis, b) monitoring the effect of elevated and decreased gene expression levels on growth, c) identifying the location of the gene product and d) revealing interference with known developmental pathways. Especially a) and b) require detailed knowledge on gene expression levels and the time course of changes in these levels by several treatments.

Researcher(s)

• Promoter: Vissenberg Kris

Research team(s)

• Integrated Molecular Plant Physiology Research (IMPRES)

Project type(s)

• Research Project

Abstract

This project will produce mathematical models of root development in Arabidopsis thaliana integrating the molecular regulation of cell division activity, cell elongation and transport of hormones with growth and architectural and mechanical characteristics of roots.

Researcher(s)

• Promoter: Vissenberg Kris
• Fellow: De Vos Dirk

Research team(s)

• Integrated Molecular Plant Physiology Research (IMPRES)

Project type(s)

• Research Project

Abstract

This project represents a formal research agreement between UA and on the other hand the Flemish Public Service. UA provides the Flemish Public Service research results mentioned in the title of the project under the conditions as stipulated in this contract.

Researcher(s)

• Promoter: Adriaensen Dirk
• Co-promoter: Bogers John-Paul
• Co-promoter: Timmerman Vincent
• Co-promoter: Vissenberg Kris

Research team(s)

• Laboratory of cell biology and histology

Project type(s)

• Research Project

Abstract

The Arabidopsis hypocotyl has two growth phases. During the first phase, all cells grow slowly and synchronous and they are 'prepared' to start the second phase. During the fast asynchronous growth, cells elongate dramatically. Based on micro-array results specific differentially expressed genes that allow cells to start and proceed through the second growth phase are studied.

Researcher(s)

• Promoter: Vissenberg Kris

Research team(s)

• Integrated Molecular Plant Physiology Research (IMPRES)

Project type(s)

• Research Project

Abstract

The project aims to study the role of genes in the development of Arabidopsis roothairs. 151 genes were identified, many having a role in cell wall metabolism. The phenotype of knock-out plants will be investigated, as well as cell wall composition, expression patterns, the effect of overexpression on the phenotype and the localisation of the geneproducts of interesting genes. If necessary, interesting lines will be crossed into mutant backgrounds or in plants with fluorescent markers.

Researcher(s)

• Promoter: Vissenberg Kris

Research team(s)

• Integrated Molecular Plant Physiology Research (IMPRES)

Project type(s)

• Research Project

Abstract

The size and form of plants largely depend on the process of expansion that follows cell formation in the meristems. Using data from several available micro-array experiments the project aims to study genes with a function in the elongation of the Arabidopsis root. A reverse genetics approach coupled to an in depth analysis of the genes will reveal their precise role in the elongation process.

Researcher(s)

• Promoter: Vissenberg Kris

Research team(s)

• Integrated Molecular Plant Physiology Research (IMPRES)

Project type(s)

• Research Project

Abstract

The size and form of plants largely depend on the process of expansion that follows cell formation in the meristems. The project aims to study the elongation zone-specific genes of the Arabidopsis root, which were identified by micro-arrays performed on dissected elongation zones. A reverse genetics approach coupled to an in depth analysis of the genes will reveal their precise role in the elongation process.

Researcher(s)

• Promoter: Vissenberg Kris

Research team(s)

• Integrated Molecular Plant Physiology Research (IMPRES)

Project type(s)

• Research Project

Abstract

Being sessile organisms, (higher) plants need to be able to quickly respond to a broad and diverse range of biotic and abiotic stimuli. Many signal transduction-pathways therefore continuously change the plant's development and metabolism in optimal accordance with the ever-changing environment. In many circumstances the direction and extent of growth is modified. To know how these different pathways modulate growth, we need to understand the growth process itself together with its control mechanisms.

Researcher(s)

• Promoter: Vissenberg Kris

Research team(s)

• Integrated Molecular Plant Physiology Research (IMPRES)

Project type(s)

• Research Project

Abstract

Being sessile organisms, (higher) plants need to be able to quickly respond to a broad and diverse range of biotic and abiotic stimuli. Many signal transduction-pathways therefore continuously change the plant's development and metabolism in optimal accordance with the ever-changing environment. In many circumstances the direction and extent of growth is modified. To know how these different pathways modulate growth, we need to understand the growth process itself together with its control mechanisms.

Researcher(s)

• Promoter: Verbelen Jean-Pierre
• Fellow: Vissenberg Kris

Research team(s)

• Integrated Molecular Plant Physiology Research (IMPRES)

Project type(s)

• Research Project

Abstract

The root and hypocotyl of Arabidopsis serve as model systems to better understand the process of cell elongation. Using different micro-arrays, genes were identified that could play a major role in this process. Transgenic plants bearing promotor-GUS and -GFP constructs will be generated to study the expression pattern of these genes. Plants with altered levels of gene expression will serve to identify the phenotypic effects of these gene changes. All these experiments will shed more light on the precise role of the identified genes in the cell elongation process.

Researcher(s)

• Promoter: Vissenberg Kris

Research team(s)

• Integrated Molecular Plant Physiology Research (IMPRES)

Project type(s)

• Research Project

Abstract

Aim: Our research is devoted to the mechanisms that control cell elongation in seed plants and especially in roots. Given the role of roots in exploration of soil substrate, anchorage and uptake of nutrients, the expansion of root cells is necessary to develop a functional root system. The identification of certain actors in the process of cell elongation and its control is the aim of the present research proposal. It fits in the research themes of the lab that focus on different aspects of the cytoskeleton and the cell wall in relation to cell elongation (De Cnodder et aI., 2005; Kerstens en Verbelen, 2003; Le et aI., 2004; Verbelen et aI., 2005). Promotor and co-promotor have gained substantial experience in microscopy, root development and molecular biological techniques to supervise this research proposal.The body of higher plants consists of cells that are formed in meristems. Outside the meristems, these newly formed cells generally expand considerably before reaching a stage of differentiation and maturation. The development of the Arabidopsis thaliana root epidermis is well described at the meristem level, including the quiescent center and the founder cells that give rise to the epidermal cell files in the root (Benfey and Scheres, 2000; Dolan et aI., 1993; van den Berg et aI., 1998). The Arabidopsis root is useful for the study of cell elongation. It is small, exhibits a highly predictable developmental pattern and can be easily visualized (with a normal microscope). The cells that are formed in the meristem can be easily traced when they pass through the elongation zone to reach the differentiation zone. Fast elongation of these cells occurs in the zone 400-9001lm away from the root tip. In each trichoblast cell file of the epidermis a new cell enters the elongation zone every 30 min and elongates from 35 to 150llm in about 3 hours (Le et aI., 2001). Such a fast growth needs accurate control mechanisms of the cell's physiology. The cell wall needs to be loosened to permit the anisotropic growth, e.g. by the action of xyloglucan endotransglucosylase/hydrolases (XTHs, Vissenberg et aI., 2000, 2003, 2005a, 2005b) but at the same time, needs to remain strong enough to prevent lysis of the cell. Obiectives: We will identify regulatory genes that are activated at the start, the middle or the end of cell elongation depending on the transgenic line.

Researcher(s)

• Promoter: Verbelen Jean-Pierre
• Co-promoter: Vissenberg Kris

Research team(s)

• Integrated Molecular Plant Physiology Research (IMPRES)

Project type(s)

• Research Project

Abstract

From a huge collection of enhancer-trap plants with GFP expression under a plant-own promoter/enhancer, only these plants with expression in the root elongation zone will be studied. The trapped genes will be identified using TAIL-PCR, knock-out plants will be phenotypically characterized and the gene products will be localized. This research will identify genes/proteins that initiate and terminate cell elongation.

Researcher(s)

• Promoter: Vissenberg Kris

Research team(s)

• Integrated Molecular Plant Physiology Research (IMPRES)

Project type(s)

• Research Project

Abstract

Researcher(s)

• Promoter: Prinsen Els
• Promoter: Van Onckelen Harry
• Promoter: Vissenberg Kris

Research team(s)

• Integrated Molecular Plant Physiology Research (IMPRES)

Project type(s)

• Research Project

Abstract

The project aims to express cellwall enzymes in specific cell types of the Arabidopsis root. We use an inducible system in parallel with a system based on Gal4-VP16 transformed plants. The effect of this expression will be monitored to study cell growth and its control.

Researcher(s)

• Promoter: Vissenberg Kris

Research team(s)

Project type(s)

• Research Project

Abstract

Researcher(s)

• Promoter: Verbelen Jean-Pierre
• Fellow: Vissenberg Kris

Research team(s)

Project type(s)

• Research Project

Abstract

The cell wall consists of a load-bearing network of cellulose microfibrils that are tethered by interconnecting xyloglucans. The projects aim is the heterologous expression in the yeast Pichia of enzymes that modify these cross-linking xyloglucans, xyloglucan endotransglucosylase/hydrolase (XTH). Arabidopsis contains 33 genes for these enzymes of which some have a root-specific expression pattern. The enzymatic characteristics of these root-specific XTHs will be determined as well as the effect of their exogenous application to growing tissues. This will give insight into the role of XTH during cell growth.

Researcher(s)

• Promoter: Verbelen Jean-Pierre
• Co-promoter: Vissenberg Kris

Research team(s)

Project type(s)

• Research Project

Abstract

The plant cell wall, consisting of cellulose microfibrils embedded in a matrix of pectins, hemicelluloses and structural proteins, is a very rigid structure that contains the protoplast. To allow growth of this `box', tension-bearing structures (especially xyloglucans that tether microfibrils) need to be modified. Many enzymes such as expansins, xyloglucan endotransglycosylase (XET) and endo-glucanases perform important functions in this aspect. We developed a fluorescent technique that enabled us to specifically visualize XET action in elongating cells and during the onset of root hair initiation. Using this technique, we will screen a large collection of mutants impaired in elongation. The cell walls of selected mutants will be further characterized using different techniques. An expression analysis of the different XET genes in Arabidopsis will reveal the gene(s) that is (are) specifically expressed in the elongation zone of the root. Mutants overexpressing these genes and knock-out mutants will be generated and morphologically and biochemically characterized. The aim of the study is to elucidate XET's role in the expanding cell wall and to characterize XET's relation to the other enzymes mentioned above.

Researcher(s)

• Promoter: Verbelen Jean-Pierre
• Fellow: Vissenberg Kris

Research team(s)

Project type(s)

• Research Project

Abstract

The initiation of polar growth will be analysed on the level of redistribution of ions in the cytoplasm, the organisation of the cytoskeleton and the localization of growth. For this purpose we will use the tobacco single cells culture system. Afterwards the distribution and activity of plasmam membrane proton pumps will be studied.

Researcher(s)

• Promoter: Verbelen Jean-Pierre
• Fellow: Vissenberg Kris

Research team(s)

Project type(s)

• Research Project

Abstract

The initiation of polar growth will be analysed on the level of redistribution of ions in the cytoplasm, the organisation of the cytoskeleton and the localization of growth. For this purpose we will use the tobacco single cells culture system. Afterwards the distribution and activity of plasmam membrane proton pumps will be studied.

Researcher(s)

• Promoter: Verbelen Jean-Pierre
• Fellow: Vissenberg Kris

Research team(s)

Project type(s)

• Research Project