For decades, research on plant chemical defenses has focused on glandular trichomes—the tiny hair‑like structures on leaves and stems that produce and secrete protective compounds. Acyl sugars, a class of specialized metabolites widespread in the nightshade family (Solanaceae), are known to deter insects and fungal pathogens when produced in leaf trichomes.

However, the biosynthesis, structures, and biological roles of acyl sugars outside of leaves have remained largely unexplored. Given these gaps, the researchers set out to investigate whether acyl sugars are produced on fruit surfaces and, if so, how their diversity and biosynthesis compare to leaf‑produced counterparts.

Now, a collaborative team from the University of Missouri, the University of Colorado Boulder, and the University of Helsinki has mapped this chemical landscape across 28 wild tomatillo species, uncovering over 300 distinct acyl sugars on fruit surfaces. Their findings, published (DOI: 10.1093/hr/uhag177) in 2026 in Horticulture Research, show that these sticky compounds are often more abundant on fruits than on leaves—a surprising twist that challenges long‑held assumptions about where and how plants deploy chemical defenses.

Acyl sugars

The researchers performed organ‑specific metabolomics on leaf, calyx (the inflated husk surrounding the fruit), and fruit surface extracts from 28 Physalis species—the genus that includes tomatillo, goldenberry, and groundcherries. Manual annotation of mass spectrometry data identified at least 323 unique acyl sugar types across the genus, dramatically expanding the known acyl sugar diversity.

Strikingly, acyl sugars were detected on the fruit surfaces of 22 species, and in many cases they were as abundant—or even more abundant—on fruits than on leaves or calyces. This is particularly notable because most Physalis species lack glandular trichomes on their fruit surfaces, suggesting that fruit‑surface acyl sugars are synthesized and deposited through mechanisms distinct from the well‑studied trichome‑based pathway in leaves.

The study also revealed that most acyl sugar compounds are species‑specific: approximately 72% of the 323 annotated structures were found in only one species, with only 39 shared across three or more species. Phylogenetic analyses found no significant correlation between chemical profiles and evolutionary relationships, indicating that acyl sugar production has evolved independently multiple times.

Enormous diversity

The authors said, “We were surprised to find such an enormous diversity of acyl sugars on fruit surfaces, especially since most of these species lack the glandular trichomes where these compounds are normally made. It suggests that plants have evolved completely different ways of deploying chemical defenses on fruits versus leaves.”

They added, “The fact that acyl sugar profiles don’t follow the evolutionary tree tells us that this trait is highly labile—species are constantly inventing new chemical combinations, which may help them stay one step ahead of herbivores and pathogens.”

The findings have direct implications for agricultural resilience. Since acyl sugars deter insect herbivores and fungal pathogens, engineering fruit‑surface acyl sugar production into other berry crops—such as tomatoes, which are closely related to Physalis—could provide a built‑in defense layer without relying on synthetic pesticides.

First step in biosynthesis

The study also characterized three Physalis acyl sugar acyltransferase (ASAT) enzymes, the first step in acyl sugar biosynthesis, and found they have broad substrate preferences—a biochemical flexibility that may explain the vast chemical diversity observed.

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Understanding how these enzymes work could allow researchers to engineer specific acyl sugar profiles tailored to different pest pressures or environmental conditions.

Moreover, the finding that fruit and calyx acyl sugar accumulation are not correlated suggests they are under independent genetic control, opening the door to tissue‑specific engineering strategies.

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