[The albino mechanism of a new theanine-rich tea cultivar 'Fuhuang 2'].

To explore the mechanism of tea albino variation and high theanine formation, 'Fuyun 6' and a new theanine-rich tea cultivar 'Fuhuang 2' were as materials in this study, pigment content, metabolome and transcriptome of the two cultivars were analyzed by ultramicroelectron microscopy, widely targeted metabolomics, targeted metabolomics and transcriptomics. The results showed that five catechins, theobromine, caffeine, and 20 free amino acids, including theanine, glutamine, arginine, etc., were identified by targeted metabolomics. The amino acid content of 'Fuhuang 2' was significantly higher than that of 'Fuyun 6', and the theanine content was as high as 57.37 mg/g in 'Fuhuang 2'. The ultrastructure of leaves showed that the chloroplast cell structure of 'Fuhuang 2' was fuzzy, most of the grana lamellae were arranged in disorder, with large gaps, and the thylakoids were filiform. The determination of pigments showed that compared with 'Fuyun 6', the contents of chlorophyll A and B, carotenoids, flavonoids and other pigments of 'Fuhuang 2' decreased significantly, some important pigment-related-genes, such as chlorophyllase (CLH), 9-cis-epoxycarotenoid dioxygenase (NCED), flavonoid 3ß-hydroxylase (F3H) and flavonoid 3', 5'-hydroxylase (F3'5'H) were significantly changed. Compared with 'Fuyun 6', 'Fuhuang 2' identified 138 significantly changed metabolites (SCMs) and 658 differentially expressed genes (DEGs). KEGG enrichment analysis showed that SCMs and DEGs were significantly enriched in amino acid biosynthesis, glutathione metabolism and TCA cycle. In general, the albino phenotype of 'Fuhuang 2' may be caused by a deficiency in photosynthetic proteins, chlorophyll metabolism genes and chlorophyll content. The accumulation of high theanine in 'Fuhuang 2' may be due to the low nitrogen consumption in yellowed leaves and the lack of carbon skeleton, amino and nitrogen resources are stored more effectively, resulting in the up regulation of metabolites and related gene expression in the amino acid synthesis pathway, theanine has become a significant accumulation of nitrogen-containing compounds in yellowed leaves.

Identification of Co-Expressed Genes Related to Theacrine Synthesis in Tea Flowers at Different Developmental Stages.

Jiaocheng kucha is the first reported tea germplasm resource which contains theacrine founded in Fujian Province. Currently, the anabolic mechanism of theacrine within tea leaves is clear, but there are few studies focused on its flowers. In order to further explore the mechanism of theacrine synthesis and related genes in flowers, current study applied Jiaocheng kucha flowers (JC) as test materials and Fuding Dabaicha flowers (FD) as control materials to make transcriptome sequencing, and determination of purine alkaloid content in three different developmental periods (flower bud stage, whitening stage and full opening stage). The results showed that the flower in all stages of JC contained theacrine. The theacrine in the flower bud stage was significantly higher than in the other stages. The differentially expressed genes (DEGs) at three different developmental stages were screened from the transcriptome data, and were in a total of 5642, 8640 and 8465. These DEGs related to the synthesis of theacrine were primarily annotated to the pathways of purine alkaloids. Among them, the number of DEGs in xanthine synthesis pathway was the largest and upregulated in JC, while it was the smallest in caffeine synthesis pathway and downregulated in JC. Further weighted gene co-expression network (WGCNA) indicated that ADSL (CsTGY03G0002327), ADSL (CsTGY09G0001824) and UAZ (CsTGY06G0002694) may be a hub gene for the regulation of theacrine metabolism in JC. Our results will contribute to the identification of candidate genes related to the synthesis of theacrine in tea flowers, and explore the molecular mechanism of theacrine synthesis in JC at different developmental stages.