O-Linked Oligosaccharides in Plant Specialized Metabolites

Glycosylation is a widespread modification of plant specialized metabolites (PSMs), yet O-linked oligosaccharide chain formation remains poorly explored. Beyond mono-glycosylation, a subset of PSMs occurs as di-, tri-, or higher oligosaccharides conjugates in which multiple sugar units are sequentially attached at a single glycosylation site. Such chain-based architectures have been reported across diverse plant taxa and chemical classes, but remain sparsely documented. Here, we synthesize evidence for O-linked polysaccharides in PSMs, with emphasis on their chemical architectures and biosynthetic principles. Finally, we discuss emerging examples in which O-linked oligosaccharide chains modulate metabolite stability, reversibility, or chemical behaviour, positioning poly-glycosylation as an underappreciated dimension of plant chemical diversity.