Susanne Hoffmann-Benning
Research Assistant Professor
- M.S. 1988, Albert-Ludwigs Universitaet, Freiburg, Germany
- Ph.D. 1993, Michigan State University
- Postdoctoral Researcher, 1993-97, Institut fuer Genbiologische Forschung Berlin GmbH, Berlin, Germany
- Visiting Research Associate, 1998-2002 Michigan State University
- Co-Manager, 2002-2004, MSU-Mass Spectrometry Facility
hoffma16@msu.edu
120 Biochemistry Building
Michigan State University
East Lansing, MI 48824-1319
Office: 517-355-9644
Lab: 517-432-9281
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Susanne Hoffmann-Benning Research Interests
While we are generally interested in the characterization of compounds, which are important for plant growth and development, our main research focuses on two aspects of plants:
- I) The mechanism of phloem transport and its role during long-distance signaling, and
- II) The changes in the plant cell wall and cuticle during rapid tissue expansion
I) The plant phloem plays a crucial role in assimilate and nutrient transport, pathogen response, and in plant growth and development. It contains a multitude of compounds: small molecules, peptides and proteins, nucleic acids, and lipids. Yet, few species have yielded pure phloem exudates, and if proteins need to be analyzed, those species tend not to have sequenced genomes, making identification difficult. We are using proteomics and other mass spectrometry tools to characterize the proteins, metabolites and lipids present in the phloem exudate of Perilla ocymoides and Arabidopsis thaliana. We are now starting to analyze the expression and distribution of proteins, mRNAs and lipids that could possibly involved in the long-distance signaling in plants.
We were able to obtain pure phloem exudate from Arabidopsis thaliana in amounts large enough to allow for simultaneous metabolite and protein analysis. Using our method, we will now be able to isolate and unambiguously identify proteins present in the Arabidopsis phloem sap and study their function. This combined approach, while more elaborate and time-consuming, can yield new and important aspects of phloem transport and lead to a better understanding of previously undescribed proteins found during large-scale proteomics analyses. We were able to detect several regulatory systems, some of which had not been described before in sieve elements: (I) A phospho-myo-inositol-dependent system possibly involved in the regulation of phosphate homeostasis, (II) a lipid-binding/transport system and (III) the presence of mRNA as well as several RNA-binding proteins as an explanation for stable mRNA transport in the sieve elements. We are now in the process of analyzing several of the proteins as well as the mRNA population found in the phloem.
II) Plant cells are surrounded by the cell wall and, where the tissue meets the environment, are covered by the cuticle. While the cell wall is largely composed of interconnected carbohydrates and proteins, the structural component of the cuticle is cutin, a polyester compound composed mainly of C16- and C18- hydroxy and epoxy fatty acids. The cell wall plays a role in regulating the degree of cell- and organ expansion; it gives the plant stability/structure, and it is a barrier against pathogen infection. The cuticle is essential for proper organ formation, a barrier to water loss and pathogen entry, and - as we have shown - also plays a role in regulating plant growth. We are using proteomics to identify proteins that are enriched in the outer epidermal cells of rapidly growing corn coleoptile and will be testing their expression and role during plant growth. The changes in the plant cell wall and cuticle during rapid tissue expansion.
Rapidly growing corn coleoptiles display a phenomenon called “tissue tension”. When they are cut longitudinally, they curve outwards with the epidermis on the concave side of the section. Tissue tension has been interpreted as the manifestation of two conflicting forces: the epidermis is under tension because it is growth limiting, while the inner tissue does not limit growth and is under compression. During examination of the cell ultrastructure of rapidly growing plants, osmiophilic particles (OPs) had been observed in several plant species. These particles are 80-300nm in diameter. Electron microscopy and labeling experiments had shown that they are closely associated with the outer epidermis of growing tissues, are going through the secretory pathway, and are, at least in part, proteinaceous. From their location and time of appearance we can assume that they are related to either cell-wall or cuticle biosynthesis. As precursors of the plant cuticle, they would be essential in multiple ways: in addition to playing a role in plant growth, they may be important in the defense against pathogens and in the prevention of water loss. We used a proteomics approach to try to identify novel proteins involved in regulating plant growth via cell wall or cuticle biosynthesis by comparing the protein profile of slow versus rapidly growing coleoptile and coleoptile epidermis.
We were able to identify over 80 proteins that appear to be induced in rapidly growing coleoptile epidermis. Half of those are related to protein synthesis/maintenance and 11% are potentially associated with the cell wall, cuticle, or lipid metabolism. We are now analyzing the expression and distribution of the latter proteins plus an additional three hypothetical proteins with unknown function.