Poster: Proteomics

Abs # 968: A proteomic investigation of alfalfa cell wall proteins in relation to lignification

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

The plant cell wall is a dynamic structure composed of an intricate matrix of polysaccharides, proteins, and phenolic compounds. Lignin, a complex phenylpropanoid polymer, is a major component of secondary cell walls that is deposited during maturation of vascular plants. The monolignol subunits are synthesized in the cytoplasm, transported to the cell wall and polymerized there by oxidative coupling. Both peroxidases and laccases have been proposed as the enzymes catalyzing lignin polymerization, and other cell wall proteins are suspected to be initiation sites for lignification. Unfortunately, there is little definitive data on the involvement of cell wall proteins in lignin biosynthesis, especially in non-woody herbaceous plants such as alfalfa. We are utilizing a proteomics approach and a COMT (caffeic acid 3-O-methyltransferase) down-regulated alfalfa line to investigate the population of proteins in the cell walls of lignifying stems. This transgenic alfalfa line displays decreased lignin content and a unique ratio of monolignol subunits, and thus may help shed light on the proteins involved in lignin biosynthesis. Several extraction and fractionation protocols for cell wall proteins will be presented. Proteins isolated from the cell wall fraction of alfalfa stems have been separated by two-dimensional electrophoresis and identified using LC/MS/MS. The identified proteins include glucosidases, peroxidases, malate dehydrogenase, proline rich protein, an extensin homolog and acid phosphatase. Possible roles for these proteins in the cell wall and in lignin biosynthesis will be discussed.