Structurally diverse acylsugars on wild tomatillo fruit surfaces

Plants have evolved a structurally diverse chemical repertoire to mediate various environmental interactions. Yet, little is known about the chemical complexity and metabolic pathways across many plant genera. Acylsugars are a class of specialized metabolite widely distributed across the Solanaceae that play a role in deterring herbivores, insects, and fungal pathogens. Although acylsugars have been extensively characterized from leaf glandular trichomes, they have also been detected in other organs. Nevertheless, the biosynthesis, structures, and function of acylsugars outside of leaf trichomes remain unknown. Here, we performed organ-specific metabolomics across 28 Physalis species, an emerging model and crop genus closely related to important Solanum crops. Automated feature extraction revealed thousands of mass spectral features across the different species and organs. Acylsugar mass spectral features were manually annotated from surface extracts, revealing at least 323 unique acylsugars, substantially expanding the known acylsugar diversity in the Physalis genus. Some, but not all, species in the Physalis genus accumulated acylsugars on the trichome-less fruit surface, and acylsugars were as abundant or sometimes more abundant in fruits than in leaves or calyces. Hierarchical clustering and phylogenetic tests indicated that species with similar acylsugar profiles did not cluster taxonomically. To determine the biochemical mechanism underlying acylsugar structural diversity, we characterized the first step of acylsugar biosynthesis, catalyzed by an acylsugar acyltransferase (ASAT). Three Physalis ASAT1 homologs displayed broad substrate preferences, which may partially explain the differences in acylsugar profiles. The diverse fruit-localized acylsugars across the Physalis genus can inform engineering strategies for increased crop resilience.