Poster: Cell walls

Abs # 604: A Proteomic Investigation of Alfalfa Cell Wall Proteins

Presenter:	Watson, Bonnie S., bowatson@noble.org
Authors	Watson, Bonnie S. (A)   Lei, Zhentian  (A)   Dixon, Richard A. (A)   Sumner, Lloyd W. (A)
Affiliations:	(A): The Samuel Roberts Noble Foundation

Although plant cell walls consist primarily of carbohydrates, proteins compose approximately 10% of the cell wall mass. These proteins are important in structure, growth and development, defense, and signaling. In general, there is little definitive data about the proteins that populate cell walls. This is, at least in part, due to several problems inherent in isolating and identifying cell wall proteins (CWPs). First, separating CWPs from soluble and membrane-associated proteins is challenging. Second, CWPs are known to be glycosylated and are often very basic, which frequently results in problematic isoelectric focusing and PAGE. Third, during the extraction of proteins from the walls of mature plant tissues, other materials such as polysaccharides and polyphenolics are coextracted. These materials can result in streaking and background staining on 2-DE gels, making analyses of the proteins separated by 2-DE difficult or impossible. Using alfalfa stems as a model, we have developed an extraction method for CWPs that appears to be free of contaminating proteins and exhibits only slight background staining on 2-DE gels. By combining 2-DE with LC/MS/MS and bioinformatics, we have identified a large number of proteins that provides a more comprehensive view of the proteins composing plant cell walls. Proteomic comparisons of young alfalfa stems containing only primary walls to older stems containing secondary walls and lignified tissue will be utilized to evaluate developmental differences in the population of CWPs. Transgenic alfalfa lines containing unique ratios of monolignol subunits are also being examined for differences in cell wall protein populations which could be associated with varying lignin content.