Transcription factors CsWRKY53 and CsWRKY40 synergistically regulate l-theanine hydrolysis via the abscisic acid signaling pathway during tea withering.

Abstract

l-Theanine hydrolysis in tea (Camellia sinensis) leaves not only reduces the quality of tea products but also decreases their health benefits. Postharvest dehydration-induced abscisic acid (ABA) contributes to l-theanine hydrolysis, but the specific underlying mechanism has not been explored. Based on transcriptome analysis and gene silencing experiments, CsNCED3a was shown to be a key gene for ABA synthesis in harvested tea leaves, and CsABF7 up-regulated the expression of CsWRKY40, which encodes a transcription factor that directly regulates a l-theanine hydrolysis gene, resulting in the loss of l-theanine. CsWRKY53 and CsWRKY40 activated the expression of CsNCED3a. The CsWRKY53-CsWRKY40 complex exhibited a stronger regulatory effect than the individual transcription factors. These findings reveal an ABA-mediated regulatory pathway for l-theanine hydrolysis, and highlight the pivotal role of ABA in the postharvest metabolism of critical flavor-contributing metabolites in tea leaves.