The Laboratory of Cell Biology explores selected molecular regulatory modules of plant cell polarity and morphogenesis operating mostly at the plasma membrane, at the interface of secretory pathway, membrane lipids and cytoskeleton. Plant morphogenesis is based essentially on two processes - oriented cell division and differential cell growth. As model plants we use angiosperm Arabidopsis and tobacco along with moss Physcomitrella patens. We focus on intracellular molecular mechanisms driving cellular morphogenesis such as exocytosis. Proteins participating in these mechanisms are, despite major differences in cell structure and behaviour, often very similar to those found in the fungal and animal kingdoms. The laboratory is centered around the detailed characterization and regulation of the plant vesicle tethering complex exocyst in various cell types across plant species, including plant-pathogen interactions. A significant aspect of the research is understanding of minor membrane lipids in the maintenance and establishment of cell polarity.
The Exocyst Complex
Exocyst is a hetero-octameric protein tethering complex that provides the first contact between a vesicle and a destination membrane. The complex assembles from subunits SEC3, SEC5, SEC6, SEC8, SEC10, SEC15, EXO84 and EXO70 and works as an effector of small GTPases. In plants as in model organism which went over several genome duplication events are the subunits present in more copies. Our team has the special aim of understanding of exocyst mechanism and diversification in plants as well as its evolution. Therefore we study its behavior and functions in Bryophytes Physcomitrella patens and liverwort Marchantia polymorpha. Together with a diversification of plant body in the evolution of land plants Embryophytes have diversified peripheral subunit EXO70. The EXO70 family counts for example 23 paralogs in Arabidopsis thaliana, 15 in Vitis vinifera and even 47 in Oryza sativa. We use mostly model plant Arabidopsis thaliana to answer unresolved questions about the complex diversification, dynamics, interaction partners and lipids binding in the context of plant development and morphogenesis. We focus as well on its role in unconventional secretion pathways.
Small GTPases form a family of monomeric proteins that control many polarized processes within the plant cell. We focus on the RAB GTPase subfamily connected with membranes via double geranylgeranyl anchors.
RAB GTPases are currently extensively studied as important regulators of the intracellular vesicular transport. Using biochemical, molecular biological and genetic approaches, we study RAB GTPases involved in terminal steps of exocytosis – especially those regulating the exocyst complex. We attempt to identify interactors of such RABs as a tool to determine a particular role of different RABs in the plant cell.
Furthermore, we study RAB GDP dissociation inhibitors (RAB GDI) that belong to basic regulators of small GTPases with redundant functions and play an essential role in the plant cell.
Anionic Phospholipids in Cell Polarity
Membrane phosphoinositides and phosphatidic acid, along with lipases, kinases, and phosphatases, are known controllers of cell polarity and vesicular trafficking in yeast and animal cells. Phospholipids function in eukaryotic cells both as classical "second messengers" and as localization cues, enabling the recruitment of phospholipid-binding proteins to specific membranes or membrane domains. We use a growing pollen tube model to address the relationship between these two aspects of membrane lipid function, especially as related to substrates and products of phospholipase D in plant cell polarization (Potocký et al. 2003). We described the reciprocal character of regulation of phospholipase D activity and actin dynamics restricted to PIP2-dependent PLDβ, and suggest that this PLD–actin interaction is important for general tip growth of plant cells (Pleskot et al. 2010). We are currently studying the involvement of other PLD isoforms in pollen tube growth and trying to describe the complex dynamics of various signaling lipids during the establishment and maintenance of polar cell expansion.