Cell walls of the Arabidopsis mutant mur2 contain less than 2% of the wild-type amount of fucosylated xyloglucan because of a point mutation in the fucosyltransferase AtFUT1. The mur2 mutation eliminates xyloglucan fucosylation in all major plant organs, indicating that Arabidopsis thaliana fucosyltransferase 1 (AtFUT1) accounts for all of the xyloglucan fucosyltransferase activity in Arabidopsis. Despite this alteration in structure, mur2 plants show a normal growth habit and wall strength. In contrast, Arabidopsis mur1 mutants that are defective in the de novo synthesis of l-fucose exhibit a dwarfed growth habit and decreased wall strength [Reiter, W. D., Chapple, C. & Somerville, C. R. (1993) Science 261, 1032-1035]. Because the mur1 mutation affects several cell wall polysaccharides, whereas the mur2 mutation is specific to xyloglucan, the phenotypes of mur1 plants appear to be caused by structural changes in fucosylated pectic components such as rhamnogalacturonan-II. The normal growth habit and wall strength of mur2 plants casts doubt on hypotheses regarding roles of xyloglucan fucosylation in facilitating xyloglucan-cellulose interactions or in modulating growth regulator activity.