Sticky business: the intricacies of acylsugar biosynthesis in the Solanaceae

Plants display tremendous chemical diversity. Like all organisms, they possess a core set of metabolites for growth and development. However, plants are notorious for their specialized chemical repertoire. Biologically active specialized metabolites enable plants to interact with their environment and provide humans with diverse medicines. Specialized metabolites are derived from core metabolites, often using enzymes that evolved from core pathways in a lineage-specific manner. Biochemical understanding of plant specialized metabolic pathways provides insight into the evolutionary origins of chemical diversity and tools for engineering the production of biologically active metabolites. Acylsugars are a class of specialized metabolites occurring widely in the Solanaceae and other plant families where they contribute to fitness. Although assembled from simple core metabolic precursors, sugars and acyl chains, tremendous acylsugar structural diversity is observed across the Solanaceae family. Enzymes that catalyze the esterification of acyl chains to sugar cores have been well characterized from phylogenetically diverse species, and their biochemical diversity contributes to acylsugar structural variation. The upstream metabolic pathways that provide the acyl chain precursors also contribute to acylsugar structural variation. Yet, biochemical and genetic understanding of these upstream biosynthetic pathways is less well known. Here, we focus on recent advances in acyl chain biosynthesis and elongation pathways, the subcellular distribution of acylsugar biosynthesis, and how biochemical innovations in acylsugar biosynthesis contribute to structural diversity specifically focusing on Solanaceae-type acylsugars.