Study on the formation mechanism of the key fresh aroma component (Z)-3-hexen-1-ol during the spreading process of lu’an Guapian green tea

Abstract

Introduction

The regulation of aroma quality during the postharvest processing of fresh tea leaves is a critical yet underexplored area. Green tea spreading, a key step that induces dehydration stress, significantly influences aroma formation but the underlying molecular mechanisms remain poorly understood.

Objectives

This study aimed to identify the optimal spreading degree for the fresh aroma quality of Lu’an Guapian (LAGP) green tea and to elucidate the key volatile compounds, biosynthetic genes, and regulatory transcription factors responsible for this process.

Methods

We utilized an integrated multi-omics approach, combining gas chromatography-mass spectrometry (GC–MS), gas chromatography–olfactometry-mass spectrometry (GC-O-MS), and odor activity value (OAV) analysis to profile aroma compounds. Transcriptomics was used to identify associated gene expression changes. Key findings were validated through subcellular localization, in vitro enzyme assays, transient overexpression in tea plants, promoter cloning, yeast one-hybrid (Y1H) assays, luciferase (LUC) reporter assays, electrophoretic mobility shift assays (EMSA), and exogenous ethephon treatment.

Results

An optimal moisture range of 68%–71% was found to maximize the fresh aroma quality. (Z)-3-hexen-1-ol was identified as a critical contributor, and its biosynthetic gene, CsADH1, was strongly upregulated. In vitro assays confirmed CsADH1′s cytoplasmic localization and its specific activity in converting (Z)-3-hexenal to (Z)-3-hexen-1-ol. Transient overexpression of CsADH1 in tea plants significantly increased (Z)-3-hexen-1-ol production. Furthermore, we discovered that the transcription factor CsERF105 directly binds to the CsADH1 promoter to activate its expression in response to dehydration stress and potential ethylene signal.

Conclusion

Our results demonstrate that dehydration stress and potential ethylene signal during spreading triggers CsERF105-mediated activation of CsADH1, which in turn enhances the biosynthesis of the key fresh aroma compound (Z)-3-hexen-1-ol. This study successfully links a specific spreading processing condition to a molecular regulatory module, providing crucial insights and novel targets for improving aroma quality in tea processing.