Research – Nielsen Lab


Nielsen Lab Research Focus

My lab’s current research is organized around three projects that each addresses one or more of our three aims.

The long-term aims of my research program are centered on the following three interrelated aims:

  1. Identify and characterize membrane trafficking pathways involved in polarized secretion in plant cells
  2. Determine the molecular machinery that sorts cargo for polarized secretion, especially those components involved in sorting of plant-specific polysaccharides and cell wall proteins (e.g. hemicelluloses and arabinogalactan proteins)
  3. Examine how polarization cues from neighboring cells and tissues are perceived and how they influence the subcellular orientation of plant secretory pathways

As a starting point to these investigations we are utilizing plant Rab GTPases in order to identify plant membrane compartments involved in polarized secretion. The characteristic of individual members of this family of regulatory GTPases to specifically localize to distinct subcellular membranes makes them particularly useful tools to identify plant secretory compartments that often lack well-characterized marker proteins. In addition, Rab GTPases regulate membrane trafficking steps through the specific recruitment of cytosolic “effector proteins,” which in turn are responsible for aspects of membrane trafficking such as cargo sorting, vesicle budding, and interaction with cytoskeletal elements.

My lab’s current research is organized around three projects that each addresses one or more of our three main aims. The first project involves characterization of the plant Rab GTPase, RabA4b, which localizes to membranes that are selectively recruited to the tips of actively expanding root hair cells. Identification of this compartment is important because the positioning of Rab4b-labeled membranes in the tips of actively growing root hairs implicates an involvement in the polarized delivery of cell wall components to sites of new cell wall deposition.

The second project, which has emerged from our studies of RabA4b-interacting proteins, involves examination of the role of phosphoinositides in membrane trafficking in plants. My current interest lies in examining to what extent the formation of phosphoinositide species through specific PI-kinase activities plays during sorting and budding of cell wall cargo molecules in the plant membrane trafficking system.

The third project involves understanding the role of RabA4d, a close relative of RabA4b that is exclusively expressed in pollen. We are currently interested in how the tip-localization of RabA4d-labeled membranes is controlled during the guided elongation of pollen tubes through the flower, whether it shares elements with tip-localization of RabA4b in root hairs, and how this dynamic positioning is influenced by maternal guidance cues.

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