Plant cell biology

Professor Chris Hawes, Dr David Evans, Dr John Runions 

The plant cell biology laboratories incorporate the microscopy and bioimaging facilities (TEM, SEM, fluorescence, Zeiss LSM 510 Meta confocals) of the Research School and include a fully equipped molecular/biochemistry laboratory and plant cell culture facilities. The main research theme of the group is the study of the flow of membrane, and the transport of proteins within the endomembrane system in plant cells from the nuclear envelope through to the plasma membrane, and organelle biogenesis. Major strengths of the group are in the application and development of fluorescent protein technology for the in vivo imaging of plant cells by confocal microscopy, immunocytochemistry and electron microscopy. The annual Cell Imaging course of the Royal Microscopical Society is run by members of the Group.

The cortical endoplasmic reticulum (ER) in plant cells is a highly structured dynamic network of tubules and small cisternae over which, in some tissues such as leaf epidermis, the Golgi bodies move. We have recently shown that both tubules can grow out from the network and that the surface of the ER membrane itself is moving in an actin-dependent manner. We are currently investigating the role of a number of plant specific myosins and a family of ER membrane proteins, the reticulons, in the establishment of the cortical ER during cell plate development and the maintenance of the cortical network in interphase cells. This work has been supported by the BBSRC and now by a Leverhulme Trust grant.

Plant Golgi dynamics and biogenesis:

We have previously shown that in many plant cell types the Golgi bodies are dynamic travelling over the ER network as distinct secretory units. Live cell imaging utilising fluorescence recovery after photobleaching technology has demonstrated cargo transport between the ER and Golgi. Several interlinked projects are currently being undertaken on the plant Golgi. The distribution of transferases and other enzymes within the Golgi stack are being investigated by live cell imaging and immuno-electron microscopy and the differential fate of Golgi membranes and proteins upon Golgi destruction and biogenesis is being established. In a BBSRC funded project a number of peripheral Golgi “matrix” proteins have been identified and their role in maintenance of Golgi structure and in Golgi biogenesis is being investigated. Interactions between the Golgi matrix proteins and between matrix proteins and regulatory GTPases (Rabs) are being investigated using live cell imaging and fluorescence resonance energy transfer (FRET) techniques.

The BBSRC funds a high-pressure freezing unit within the group. A BAL-TEC HPM 010 High Pressure Freezer permits the cryo-preservation of relatively large samples of biological material by subjecting specimens to 2100 bar during the freezing procedure, thus preventing the nucleation of ice crystals and specimen damage. A postdoctoral research assistant Dr Eric Hummel an expert in plant electron microscopy runs the facility with Barry Martin, the Cell Biology Laboratory Manager who has many years of experience in cryo-microscopy techniques. This facility supports the group’s endomembrane research and is also available to outside users.

The plant nuclear envelope is a surprisingly poorly understood system and the research of the group is concentrated on identifying native plant nuclear envelope proteins and studying their properties. The nuclear envelope is a dynamic system that undergoes massive changes in the cell cycle and is closely interlinked with the nucleoskeleton and cytoskeleton. While a few nuclear envelope proteins are conserved between animals, plants and yeast, many are not and there are significant differences that require exploration.

We are using fluorescent protein technology to study the location, role and traffic of newly described proteins at the nuclear envelope, especially during the cell cycle and have developed a family of fluorescent nuclear envelope probes, including the lamin B receptor. This work is in collaboration with Professor Iris Meier at Ohio State University.

Mechanisms for the targeting and retention of inner nuclear envelope proteins:

Using chimaeric fluorescent constructs of the human lamin B receptor we have undertaken studies of the mechanisms, conserved between kingdoms, that permit its faithful targeting to the plant nuclear envelope. Using data obtained from mutants in which key targeting and binding domains have been deleted, we have propose a model for inner nuclear envelope location of proteins in plants and are continuing this work with native plant proteins.

Localisation and function of novel nuclear envelope proteins in plants:

We have used bioinformatics (homology searching) to identify putative homologues of animal and yeast nuclear envelope proteins and then generated fluorescent protein constructs to study their cellular localisation. Two of the proteins identified contain domains suggesting that they are components of the a complex known as the LINC (Linker of Nucleoplasm and Cytoplasm) complex and we are investigating these proteins further, especially with respect to binding partners and to their dynamic behaviour in plants. This work is funded by the Leverhulme Trust.

As an extension of the work with photoactivatable GFP, I have recently turned my attention to other membrane systems within the cell, i.e. the plasma membrane and the tonoplast, in an attempt to compare the movement of proteins in different membrane types and to study interactions of membrane-resident proteins with the actin cytoskeleton.

A new project in the lab examines the fate of endomembranes during cytokinesis in a developmental context. We use long-term confocal imaging to observe membrane protein localisation during key stages of mitosis in intact plant tissues. In particular, we are interested in the origin of proteins that make up the reforming cell and nuclear envelope.

People

• Professor Chris Hawes - Research Group Leader
• Dr David Evans - Reader in Plant Science
• Dr John Runions - Senior Lecturer in Cell and Molecular Biology
• Dr Alex Martiniere - Postdoctoral Researcher
• Dr Imogen Sparkes - Postdoctoral Researcher
• Dr Katja Graumann - Postdoctoral Researcher
• Dr Anne Osterrieder - Postdoctoral Researcher
  
• Maria Svedunova - PhD Student
• Peng Wang - PhD Student
• Rahul Yadav - PhD Student
• Jolanta Tolkacz - PhD Student
• Jibin He - PhD Student
  

• Dr B. Satiat-Jeunemaitre, CNRS, Institut des Sciences Végétales, Gif-sur-Yvette
• Dr P. Moreau, CNRS, University of Bordeaux
• Dr I. Moore, Dept. Plant Sciences, University of Oxford
• Dr L. Frigerio, Dept. Biology, University of Warwick
• Dr J. Denecke, Dept. Biology, Leeds University
• Dr H. Steinkellner & R. Strasser, BOKU, University of Vienna
• Professor I. Meier, Ohio State University
• Dr H. McWatters, Oxford University

• Dr S. Botchway, Rutherford Appleton laboratories, Central Laser Facility

Publications:

Professor Chris Hawes

Dr David Evans

Dr John Runions