XVI International Botanical Congess

Plant cell walls play a crucial role in plant development, signal transduction, and desease resistance. Although much is known about the structure of various cell wall components, their biosynthesis is largely unknown. Hemicellulose is a heterogeneous group of branched matrix polysaccharides that bind noncovalently to the surface of the cellulose microfibrils and, therefore, shape the cell wall. Xyloglucan, the principal hemicellulose of higher plants, has a terminal fucosyl residue that is postulated to be important in establishing conformation of the polysaccharide that enhances binding to cellulose. The fucosyltransferase that adds the terminal fucosyl residue was purified from pea epicotyls. Linkage analysis of xyloglucan fucosylated using the purified enzyme showed that fucose was added to carbon 2 of galactose, the same linkage found in vivo. An amino acid sequence of peptides derived from the 60-kDa protein closely matched the predicted translation product of an Arabidopsis EST clone. A 1768-nucleotide cDNA clone encoding the entire 63.7-kDa open reading frame of the Arabidopsis clone was isolated and sequenced. Antibodies were raised against a fusion protein encoding Arabidopsis protein that detected a 62-kDa protein in Arabidopsis membrane fraction, and immunoprecipitated fucosyltransferase enzyme activity from solubilized Arabidopsis membrane proteins. Over a hundred transferases are responsible for numerous modifications that occur on plant hemicellose. Availability of this sequence offers an opportunity to identify several other putative transferases from information available from plant sequencing projects, a task that was not possible before.