A protein – dubbed GAME15 – is the missing link in the pathway that Solanum plants like potatoes use to make molecules for chemical defense: steroidal glycoalkaloids (SGAs). The findings pave the way for engineering this biosynthetic pathway into other plants, enabling innovative applications in agriculture and biotechnology. "The discovery … provides a key to engineering SGAs for food, cosmetics, and pharmaceuticals," write the authors. Plants produce a wide variety of secondary metabolites that are crucial for their growth and interactions with the environment. These compounds, characterized by their structural diversity, can have both beneficial and harmful effects on humans and the organisms that produce them. For instance, SGAs serve as potent plant defense chemicals but can reduce nutritional value for humans and pose toxicity risks to the plants themselves at high levels. Among plant families, Solanaceae stands out for producing diverse bioactive and toxic compounds, including SGAs, which are key to defense in Solanum species like potatoes, tomatoes and eggplants. Although much progress has been made in understanding SGA synthesis and function, the complete biosynthetic pathway has remained elusive, making engineering the production of SGAs into other species a challenge. Adam Jozwiak and colleagues identify GLYCOALKALOID METABOLISM15 (GAME15) as a crucial missing link in SGA biosynthesis. By conducting a phylogenetic analysis of cellulose synthase-like enzymes across various species, including Arabidopsis, Solanaceae plants, and related proteins, Jozwiak et al. found that GAME15 evolved from cell wall machinery into an endoplasmic reticulum glucuronosyltransferase that attaches glucuronic acid to cholesterol and acts as a scaffold protein for other enzymes in the SGA biosynthetic pathway. Silencing GAME15 eliminated the production of SGAs, rendering plants more vulnerable to pests.
For reporters interested in trends, a related study , published in October 2024 by Boccia et al. reports the identification of a key cellulose synthase-like protein in Solanum nigrum that directs the biosynthesis of steroidal glycoalkaloids and saponins.
