Dear Editor,Plant cells are encased by cell walls-rigid yet highly dynamic composite structures,which consist of cellulose,hemicelluloses,pectic polysaccharides,glycoproteins,and the polyphenol lignin (Somerville et al.,2004).Biosynthesis of the wall polysaccharides is facilitated by donor-and acceptorsubstrate-specific glycosyltransferases catalyzing the transfer of the sugar moiety from a nucleotide sugar to form a specific glycosidic linkage.Glycosyltransferases have been grouped into families based on primary structure,one of which is family GT77 (www.cazy.org/GT77_all.html).Members of GT77 have been implicated in the biosynthesis of the structural wall protein extensin,hydroxyproline-rich structural glycoproteins containing arabinosyl and galactosyl side chains (Supplemental Figure 1;Lamport and Miller,1971).