The polysaccharide-rich plant cell wall surrounding the protoplast is a complex, diverse, and dynamic entity of fundamental importance in plant growth and development (1). Walls are also of immense economic value, contributing to many agro-industrial processes, and are the major renewable energy resource (biomass) on our planet. The description of the biosynthetic processes involved in the assembly of the noncellulosic polysaccharides of the wall has, until the 21st century, been slow to unfold. This is especially true of the triad of pectic polysaccharides, which are widely distributed in primary walls (Fig. 1 A ; ≈10–35%) throughout the plant kingdom. The most abundant is the pectic homogalacturonan (HG), ≈70% of pectin, a homopolymer of (1–4)-α-d-galacturonic acid (GalA) residues that may be methylesterified and acetylated (2). Rhamnogalacturonan I (RG-I), ≈35% of pectin, belongs to a family of polysaccharides with a repeating backbone of (1–2)-α-l-Rha-(1–4)-α-d-GalA, with Rha residues further substituted with other oligo/polysaccharides. RG-II, ≈10% of pectin, has an HG backbone substituted with several structurally different oligosaccharide side chains (2) (Fig. 1 B ). This structural complexity imparts diverse physical and biochemical properties on pectins that are associated with important biological and industrial functions (2, 3). Thus, there are major efforts devoted to manipulating the quality and quantity of pectin and other wall polysaccharides through genetic manipulation and conventional breeding. This process would be greatly accelerated if we understood the mechanisms and control of the biosynthetic steps during their assembly and deposition into the wall, processes whose elucidation has been hampered by difficulties in identifying the biosynthetic genes and by the pleiotropic effects of many wall mutants. More than 50 glycosyltransferases (GTs) are predicted to be required for pectin synthesis (2), but until now, genes for only … E-mail: abacic{at}unimelb.edu.au