Sébastjen Schoenaers senior researcher

Research Sébastjen Schoenaers

Research team

Expertise

I study the fundamental mechanisms that control plant growth with emphasis on the auxin-driven signaling pathways that control cell wall rheology and cell wall sensing during cell elongation. Using tip-growing cells (pollen tubes, root hairs) as a model, I study receptor-like kinase signaling at the plasma membrane/cell wall interface. My work relies on a diverse set of techniques, including high resolution live-cell imaging of protein, ion- and cell wall dynamics, the study of protein-protein interaction, -omic analysis and cell wall characterization.

Integrating the processes that control cell wall biomechanics during cell growth, using CrRLK1L-regulated root hair growth as a model. 01/10/2019 - 30/09/2023

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)

Research team(s)

Project type(s)

  • Research Project

Identification of cell wall ligands for the root hair growth regulator ERULUS. 01/04/2019 - 30/03/2020

Abstract

Plant cell growth ultimately relies on controlled loosening/strengthening of the cell wall, yielding a matrix that is not too stiff, yet not too loose. Plants have evolved specific mechanisms to sense and control cell wall composition and rigidity, in the form of cell wall binding receptor proteins. In this regard, the Catharanthus roseus Receptor-like Kinase 1-like (CrRLK1L) family of plant proteins has gained major attention during recent years. Several CrRLK1L proteins control cell growth through sensing of the cell wall status during expansion. Nevertheless, the mechanisms that lie at the basis of CrRLK1L-mediated signaling remain poorly understood. In an effort to further characterize CrRLK1L-functioning we identified ERULUS (ERU), a key regulator of root hair cell expansion, and a putative sensor of cell wall rigidity. ERU loss-of-function root hairs are short an stunted, and exhibit drastic defects in cell wall composition, pectin (a cell wall polysaccharide) modification and dynamics. The degree of pectin methylesterification directly relates to the degree of cell wall rigidity. Hence, pectin modification needs to be sensed and adjusted continuously to facilitate maintained cell growth. The ERU extracellular domain is highly similar to that of the CrRLK1Ls BUDDHAS PAPER SEAL 1/2 (BUPS1/2), which directly bind pectin in vitro. More so, ERU control of root hair growth involves the CrRLK1L FERONIA (FER), which also directly binds pectin. Together, these data provide a strong case for a direct ERU-cell wall interaction. Here, we propose to use a broad-spectrum carbohydrate array to screen for ERU-specific cell wall ligands. This method has previously been used to identify/characterize antibody specificity, carbohydrate binding modules and cell wall modifying enzymes. The procedure involves cloning and heterologous expression of a His6- and GST-tagged ERU extracellular protein domain, and subsequent array analysis using a bacterial lysate containing the soluble recombinant protein. The protocol is low-risk, simple and affordable (no protein upscaling and purification). Moreover, the tagged protein construct can be used for several downstream applications aimed at identifying protein-protein and protein-cell wall interactions. This experiment will be performed during a 2 months research stay, and will bring new expertise to the IMPRES group. Moreover, the outcome of this experiment is pivotal to our ongoing research and crucial to the understanding of cell wall sensing during plant cell growth.

Researcher(s)

Research team(s)

Project type(s)

  • Research Project

Characterization of the ARF7/ARF19 mediated signal cascade regulating root hair growth. 01/10/2013 - 30/09/2017

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)

Research team(s)

Project type(s)

  • Research Project