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Vesicle tethering complex exocyst is one of the key regulators of the cell polarity and morphogenesis in eukaryotes. The complex interacts with the secretory vesicle, as well as plasma membrane, and facilitates formation of cis SNARE complex leading into fusion of the vesicle with target destination. Two of the eight exocyst subunits, the SEC3 and EXO70 are known to bind plasma membrane via protein and lipid interactors in Opisthokont model organisms. Genomes of angiosperm plants encode a surprisingly wide repertoire of EXO70 isoforms with over 20 present in both Arabidopsis and diploid tobacco genome. It has been proposed that different EXO70 isoforms would form parts of functionally distinct subtypes of the plant exocyst complex driving membrane trafficking to various membrane domains. Specific interactions of peripheral membrane proteins with particular membrane phospholipids largely contribute to targeting of cellular components to subcellular compartments and membrane domains. This thesis focuses on role of protein-lipid interactions in regulation of plant cell polarity and contributes to functional analysis of the plant EXO70 family diversity. We introduce the topic with the theoretical reviews summarizing role of protein-lipid interactions in establishing plant cell membrane domains at...

Exocyst is a protein complex involved in tethering of secretory vesicles to cytoplasmic membrane before SNARE-mediated fusion event. Its presence and function in secretory pathway has been confirmed in yeasts, animals and plants. This thesis describes some properties of Sec5, one of the exocyst subunits, in plant model Arabidopsis thaliana. Microscopic methods, including VAEM/TIRF microscopy, were used to study subcellular localization and dynamics of Sec5-GFP fusion protein. Sec5 is cytoplasmic protein that also localizes to cytoplasmic membrane, particulary in cells with high secretory activity. It strongly localizes to maturating cell plates during late cytokinesis and its localization to cytoplasmic membrane partially depends on actin cytoskeleton. Generally, obtained results are in agreement with corresponding observations of behavior of other exocyst subunits in plant cells, suggesting, that Sec5 executes its function as part of the exocyst complex.

Cytoskeleton is known to participate in exocytosis of yeast and animal cells. The role of plant cytoskeleton during exocytosis has not been fully understood yet. However, both actin and microtubules evidently contributes to the secretion of specific cargo proteins or cell wall components. Plant cytoskeleton influences the dynamics of exocytosis through various functions. First, secretory vesicles are delivered near the plasma membrane. Second, microtubules were shown to mark the place of exocytosis. Third, cytoskeleton is able to prevent membrane fusion by simple separation of compartments. Fourth, cytoskeleton potentially mediates the interaction between molecules of secretory apparatus. Secretion of certain cargo molecules appears to be dependent on different cytoskeleton types and the exocytosis seems to be specifically regulated in each tissue. This thesis aims to describe interplay of cytoskeleton and secretory pathway on the example of tip growth and to predict future direction of research on secretory pathway based on cellulose synthase secretory data.

The cells are able to acquire variety of shapes, in which cytoskeleton plays an important role. Cytoskeleton influences deposition of cell wall materials, regulates vesicle movement in cell, participates in exocytosis and endocytosis. Cortical microtubules affect celulose accumulation in cell wall and determine direction of cell expansion, although the exact connection between microtubules and cellulose remains unclear. Actin promotes growth and contributes to its spatial regulation in both tip ang diffuse growing cells. Actin is important for secretion in expanding cells but its exact functions in cell growth regulation are not explained yet. Analysis of mutants, spectroscopic methods, cytoskeletal drugs, fluorescence proteins and other methods are used to better understand how actin and microtubule cytoskeleton are integrated during plant cell morphogenesis. Epidermal and trichome cells of Arabidopsis thaliana are a good model of research and they are used for most studies.

The origin of lateral roots is one of the determinants of the structure of the overall architecture of the root system of plants. Individual plant species differs in point of initiation of lateral roots in the longitudinal and transverse plane of the parent root. This paper briefly summarizes the findings relating to the establishment and development of lateral roots in the model of plant Arabidopsis thaliana and on the sample of several species of ferns and monocots and dicots of literature outlines the variability that manifests itself especially during initiation of lateral roots. The ferns initiation site located in the endodermis of the parent root, for other species to form the lateral root primordium of pericycle cells that are found in a certain position in relation to vascular elements in the central cylinder of the parent root. Another highly variable factor in the development of lateral root initiation site is the distance from the root apical meristem, which is related to the place of the auxin signal competent cells and also the rate of growth and progress of cells from the parent root apical meristem. Powered by TCPDF (www.tcpdf.org)