Transcriptome Insight Into the Identification of Novel Luteolin 7-O-Glucosyltransferase From Lonicerae Japonicae Flos Under Salt Stress.

Abstract

Introduction: Salt stress represents a critical abiotic constraint affecting the growth of medicinal plants and secondary metabolite biosynthesis. While glycosylation plays an established role in plant stress adaptation mechanisms, the specific functional contributions of uridine diphosphate glycosyltransferases (UGTs) to salt stress responses remain insufficiently characterized. Cynaroside (luteolin 7-O-glucoside) is a pharmaceutically valuable flavone glycoside demonstrating enhanced accumulation under saline conditions, and the coordinated upregulation of UGTs in salt-stressed Lonicerae Japonicae Flos (LJF) prompted an investigation into specific glycosyltransferases mediating this stress-induced metabolic response.

Objective: This study aims to identify and functionally characterize the UGTs involved in the biosynthesis of cynaroside in LJF under salt stress.

Methods: The transcriptomes and metabolomes of LJF under salt stress were comprehensively analyzed to identify candidate UGTs. Then, heterologous expression in Escherichia coli, protein purification technology, enzyme catalysis experiments, and molecular docking were conducted to further verify its catalytic activity.

Results: A novel glycosyltransferase was identified from LJF. Functional characterization demonstrated the recombinant enzyme's capacity to catalyze luteolin glycosylation, producing cynaroside through regioselective glucose conjugation. Molecular docking simulations revealed stable binding of luteolin to Lj7OGT3's conserved PSPG motif (plant secondary product glycosyltransferase signature domain), providing structural insights into its catalytic mechanism.

Conclusion: This study identified the role of Lj7OGT3 in enhancing cynaroside production under salt stress, which further deepened our understanding of stress-responsive secondary metabolism. Simultaneously, expanding the database of plant functional glycosyltransferases. These findings provide a biochemical foundation for engineering stress-resilient medicinal plants and developing biotechnological platforms for optimized production of bioactive glycosides.