Pseudoenzyme Role in Indole Biosynthesis Revealed in Flowering Plants

In a groundbreaking study published on June 26, 2025, in *Nature Chemical Biology*, researchers from the Max Planck Institute for Chemical Ecology have uncovered a novel mechanism by which flowering plants synthesize indole, a crucial compound in plant defense and communication. The study highlights the role of a pseudoenzyme known as TSB-like, which diverges from the traditional enzymatic pathways known in other plant species.

Indole is a nitrogen-containing aromatic compound that serves as a precursor in the biosynthesis of tryptophan, an essential amino acid, and plays a significant role in the production of various metabolites involved in plant defenses against herbivores and pathogens. According to Matilde Florean, the study's first author, the research reveals that while many plants utilize active enzymes for indole biosynthesis, core eudicot flowering plants employ a more efficient mechanism involving the pseudoenzyme TSB-like.

Traditional enzymatic pathways typically involve the active enzyme TSB (tryptophan synthase beta subunit), which facilitates the production of tryptophan from indole. However, in this newly identified pathway, TSB-like binds to another enzyme, TSA (tryptophan synthase alpha subunit), but does not catalyze the conversion to tryptophan. Instead, this interaction allows indole to be released as a volatile compound or utilized in the synthesis of specialized defense compounds. Tobias Köllner, the head of the research team, noted, "This surprising finding alters our understanding of how plants can divert enzymatic activity to enhance their resilience and attract beneficial organisms."

The implications of this discovery extend beyond academic interest. Understanding the regulatory mechanisms of pseudoenzymes like TSB-like could lead to advancements in agricultural practices, allowing for the targeted breeding of plants that are more resilient to pests while being attractive to pollinators. "Unraveling how core eudicots produce indole is vital for modern agriculture, as it could lead to crops that require fewer chemical inputs and are more sustainable," stated Sarah O'Connor, head of the Department of Natural Product Biosynthesis at the Max Planck Institute.

This research underscores the complexity of plant chemical signaling and defense mechanisms, suggesting that pseudoenzymes, which are often overlooked due to their lack of catalytic activity, may play crucial roles in plant metabolism. The findings open up new avenues for research into plant biochemistry and the potential applications in enhancing crop resilience against environmental stressors.

This study not only highlights the intricacies of plant biochemistry but also emphasizes the need for further exploration into the functions of pseudoenzymes, which can account for up to 10% of the plant proteome. The research team plans to investigate how these pseudoenzymes are regulated within plant systems and how their activity can be harnessed for agricultural innovations. As scientists continue to decode the complexities of plant metabolism, the potential for developing more resilient crop varieties becomes increasingly promising, paving the way for sustainable agricultural practices in the future.