Methods for altering the N-glycosylation pattern of proteins in higher
plants are provided. The methods comprise introducing into the plant a
recombinant construct that provides for the inhibition of expression of
.alpha.1,3-fucosyltransferase (FucT) and .beta.1,2-xylosyltransferase
(XylT) in a plant. Use of these constructs to inhibit or suppress
expression of both of these enzymes, and isoforms thereof, advantageously
provides for the production of endogenous and heterologous proteins
having a "humanized" N-glycosylation pattern without impacting plant
growth and development. Stably transformed higher plants having this
protein N-glycosylation pattern are provided. Glycoprotein compositions,
including monoclonal antibody compositions, having substantially
homogeneous glycosylation profiles, and which are substantially
homogeneous for the G0 glycoform, are also provided.