Abstract
Theanine (thea) is a unique non-protein amino acid in tea plant (Camellia sinensis) and one of the most important small molecular compounds for tea quality and health effects. The molecular mechanism that maintains thea biosynthesis is not clear but may be reflected in complicated biological networks as other secondary metabolites in plants. We performed an integrative transcriptomic analysis of tea seedlings bud and leave over the time-course of ethylamine (EA) treatment that activated thea pathway. We identified 54 consistent differentially expressed genes (cDEGs, 25 upregulated and 29 downregulated) during thea activation. Gene Ontology (GO) functional enrichment analysis of upregulated genes and downregulated genes showed that they may function as a cascade of biological events during their cooperative contribution to thea biosynthesis. Among the total cDEGs, a diversity of functional genes (e.g., enzymes, transcription factors, transport and binding proteins) were identified, indicating a hierarchy of gene control network underlying thea biosynthesis. A gene network associated with thea biosynthesis was modeled and three interconnected gene functional modules were identified. Among the gene modules, several topologically important genes (e.g., CsBCS-1, CsRP, CsABC2) were experimentally validated using a combined thea content and gene expression analysis. Collectively, we presented here for the first time a comprehensive landscape of the biosynthetic mechanism of thea controlled by a underling gene network, which might provide a theoretical basis for the identification of key genes that contribute to thea biosynthesis.
Highlights
Theanine is a non-protein amino acid that was first discovered in the leaves of tea plant (Camellia sinensis) [1]
We found a number of transcription factors (TFs) genes (e.g., NAC, bZIP) that may act as regulatory switches in thea biosynthesis
Our results indicated that the majority of these consistent differentially expressed genes (cDEGs) were significantly enriched in different enzyme activities and metabolic processes despite of minor differences between upregulated genes and downregulated genes, e.g., upregulated genes tend to have the biological function as hydrolase and transferase, and downregulated genes instead tend to have the biological function as transporter and symporter, indicating that upregulated genes and downregulated genes may behave as a cascade of biological events during their cooperative contribution to thea biosynthesis
Summary
Theanine (thea) is a non-protein amino acid that was first discovered in the leaves of tea plant (Camellia sinensis) [1]. In 2018, the genomic dissection of tea plant combined with targeted gene functional analysis revealed a TS candidate (named CsTSI) that had an evidence of thea synthetase activity [17]. We designed a time-series transcriptome sequencing of tea seedlings bud and leave, and identified 54 consistent differentially expressed genes (cDEGs) over the time-course of ethylamine (EA) treatment, which has been demonstrated to promote thea accumulation as its biosynthetic precursor in vivo tea plant [17]. Among the total 54 cDEGs, different types of functional genes, including enzymes, TFs, transport and binding proteins, were distributed, suggesting a complicated gene control network involved in thea pathway. Our results highlighted the underlying genes and their interaction patterns involved in thea pathway, providing a valuable platform for the further exploration of molecular mechanisms that drive thea biosynthesis
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