The aim of this study was to analyze metabolic and transcriptional mechanism of etiolated variation in tea plant, and to explore the albino mutation of a new homotheanine tea cultivar Fuhuang 1 and its formation mechanism of homotheanine.

The experimental materials were Fuan Dabaicha and Fuhuang 1. The combined analysis of ultramicroelectron microscopy, widely targeted metabolism, targeted metabolomics and transcriptomics was used to clarify the pigments, metabolism and transcriptome data related to the albino tea.

The results of ultrastructure showed that the chloroplast thylakoids of Fuhuang 1 was filamentous, with irregular arrangement of basal granule lamellae and many abnormal vesicles. Chlorophyll a and chlorophyll b content, chlorophyll a/b ratio, SGR gene expression and light-harvesting chlorophyll a/b protein (LHC) expression were significantly reduced in yellow leaves. Although the total content of carotenoids did not change significantly, the content of each component changed significantly. Zeaxanthin was the only component with significant increase, and the expression of its regulatory gene VDE was significantly up-regulated, and the content of other components decreased. Compared with Fuan Dabaicha, 680 differentially expressed genes (DEGs) and 57 significantly changed metabolites (SCMs) were identified in Fuhuang 1. KEGG enrichment analysis showed that SCMs and DEGs were significantly enriched in pathways related to amino acid biosynthesis, glutathione metabolism and TCA cycle. In addition, the pathways related to carbon and nitrogen metabolism were also activated. A total of 19 free amino acids were identified by targeted determination. The free amino acid content of Fuhuang 1 was 97.13 mg∙g^-1, which was significantly higher than that of Fuan Dabaicha. Theanine content was 66.90 mg∙g^-1, accounting for 68.89% of amino acids, while the content of arginine was 8.46 mg∙g^-1, which was 56.4 times as more as that of Fuan Dabaicha. The expression levels of GOGAT and GLU, which regulated amino acid synthesis, were up-regulated in Fuhuang 1 by 1.17 and 3.17 times higher than that in Fuan Dabaicha.

The leaf color of Fuhuang 1 was mainly influenced by chlorophyll, carotenoids and flavonoids. The combined action of SGR and the four LHCs might also affect chloroplast biogenesis to regulate leaf color. The content of theanine in Fuhuang 1 was significantly higher than that in Fuan Dabaicha. The main reason was that the up-regulation of ubiquitination-related protein hydrolase activity and the enhanced protein degradation ability. The biosynthesis of chlorophyll and other nitrogen-containing molecules was reduced, the carbon skeleton in yellow leaves was lacking, amino and nitrogen resources were stored more effectively. The activation of nitrogen metabolism associated with amino acid synthesis led to the accumulation of glutamate, one of the precursors of theanine synthesis. Theanine accumulated significantly in yellow leaves.