Transcriptome and Phytochemical Analysis Reveals the Alteration of Plant Hormones, Characteristic Metabolites, and Related Gene Expression in Tea (Camellia sinensis L.) Leaves During Withering.

Xu Xu,Jin Jin,Cheng Cheng,Su Su,Wang Wang,Yin Yin,Lai Lai,Zhao Zhao

doi:10.3390/plants9020204

Abstract

Plant hormones play an important role in the chemical metabolism of postharvest plants. However, alterations in plant hormones of postharvest tea and their potential modulation of quality-related metabolites are unknown. In this study, the dynamic alterations of abscisic acid (ABA), salicylic acid (SA), jasmonic acid (JA), and critical metabolites, such as catechins, theanine, and caffeine, in tea leaves were analyzed during withering from 0 to 24 h. It was found that the ABA content increased from 0 to 9 h but decreased thereafter, JA continuously increased, and the SA content showed no significant change. With the exception of gallocatechin (GC) and epicatechin (EC), the amounts of other critical components were significantly reduced at 24 h. Transcriptome analysis showed that compared with 0 h, 2256, 3654, and 1275 differentially expressed genes (DEGs) were identified at 9, 15, and 24 h, respectively. For all comparisons, DEGs corresponding to the pathways of “phenylalanine, tyrosine, and tryptophan biosynthesis” and “phenylalanine metabolism”, involved in the biosynthesis of catechins, were significantly enriched. Weighted correlation network analysis (WGCNA) of co-expression genes indicated that many of the modules were only correlated with a specific trait during the withering process; the dark olive-green module, however, was correlated with two traits, ABA and theanine. Our study indicates that withering induced dramatic alterations in gene transcription as well as levels of hormones (ABA, JA, and SA) and important components, and that ABA regulated theanine metabolism during this process.

Highlights

Tea, manufactured from the leaves of Camellia sinensis, is the second most widely consumed beverage in the world, after water [1]
There was only a slight change in salicylic acid (SA) concentration during the withering process (Figure 1c). These findings indicate that abscisic acid (ABA) and jasmonic acid (JA) may be involved in withering, while SA may not play an important role in withering
These results indicate that the amount of these critical components in tea were affected, to varying degrees, during the withering process, which is consistent with the results of previous studies [22,23,24]

Summary

Introduction

Tea, manufactured from the leaves of Camellia sinensis, is the second most widely consumed beverage in the world, after water [1]. The worldwide popularity of tea is attributable to its distinct and pleasant flavors, and to its health-promoting potential, both of which are due to the abundant metabolites that it contains, such as polyphenols, theanine, and caffeine [2]. While teas are traditionally classified as green tea, oolong tea, black tea, and pu-erh tea (or dark tea), the main manufacturing procedures are similar, which includes picking (plucking), withering (spreading), fixing (only for green tea), macerating, rolling, fermenting (oxidizing, not for green tea), and drying [3]. The dehydration stress during withering can promote the special flavors of various teas by inducing significant changes in the gene transcription and amounts of tea flavor compounds [5]

Methods

Results

Conclusion