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Cytokinesis and Cell Expansion

Image of cytokinesisTwo of the most fundamental processes in plant development are cytokinesis, by which new cells are formed, and cell expansion, by which new cells grow into the proper shape.  Both processes involve many of the same steps, including membrane trafficking along cytoskeletal elements to the site of growth, localized membrane fusion, cell wall deposition, and membrane recycling via clathrin-mediated endocytosis.  (Reviewed in Backues et al. 2007)

Our lab is interested in the fundamental mechanisms governing cytokinesis and cell expansion, and their relationship to overall plant development.  In particular, most of our work focuses on better understanding the role of membrane trafficking in plant growth.

Plant Dynamin-Related Proteins (DRP)

An essential element of both cytokinesis and cell expansion is clathrin-mediated endocytosis.  Besides its role in membrane recycling during growth, endocytosis is involved in the perception of the plant hormone brassinolide, the maintenence of auxin gradients via polar localization of the PIN proteins, and pathogen responses mediated by the flagellin receptor FLS2.  However, we know much less about the mechanisms of endocytosis in plants than in yeast and animals.

One protein involved in endocytosis in animals is the large, polymerizing GTPase dynamin.  Dynamin forms rings and spirals that wrap around the neck of the the endocytic bud and promotes membrane scission.  Dynamin is a member of a larger superfamily of polymerizing GTPases that play a number of membrane-remodeling roles in many different organisms.

Image of endocytosis

Plants are unique among organisms in the involvement of two distinct families of dynamins in clathrin-mediated endocytosis: a family of "classical" dynamins (DRP2) as well as a family of non-classical dynamin-related proteins (DRP1). 

DRP1 and DRP2 -fluorescent protein fusions label endocytic sites (left), as can be visualized in living cells by Variable Angle Epifluorescent Microscopy (VAEM).  One area of research in our lab is investigating the mechanisms of clathrin-mediated endocytosis by imaging the dynamics of endocytic sites under various conditions. 

drp1 null mutants have deficiencies in endocytosis that lead to defects in plasma membrane and cell wall structure (right).  Another area of research is the developmental roles of endocytosis, as illuminated by the phenotypes of drp1 and drp2 mutants.

In addition to its endocytic role, the DRP1 family also plays a distinct role early in the process of cell plate formation. (Click here for an overview of cell plate formation). DRP1-containing rings and spirals are seen wrapped around membrane tubules in the forming cell plate by electron tomography.  The role of these structures is not known, but they are clearly important because drp1-family mutants show cytokinetic defects (right).  This cytokinesis-specific role of the DRP1 family is of particular interest to our lab. 

Recent papers (pdfs) on the DRP1 family:
DRP1A in vitro charaterization
DRP1A and DRP1C functional redundancy
DRP1C in endocytosis
DRP1C in pollen development
DRP1 family in cytokinesis and cell expansion
DRP1A in plant development

Stomatal Cytokinesis Defective (SCD) 

This part of the website is still under construction: please see Sebastian's Faculty Page for more information on our research

CDC48: A Hexameric ATPase for Cytokinesis

Biomass Improvement for Biofuels Production