Abstract
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.
Highlights
Bitter tea is a kind of unique plant which mainly distributed in Yunnan, Hunan, Guizhou, Fujian and some other provinces of China [1]
As caffeine could convert to theacrine by oxidation at C8 and methylation at N9 in certain tea germplasm resource [5], theacrine is regarded as a downstream metabolite of caffeine
For the total amount of purine alkaloids, Jiaocheng kucha flowers (JC) was higher than Fuding Dabaicha flowers (FD) in all three stages
Summary
Bitter tea is a kind of unique plant which mainly distributed in Yunnan, Hunan, Guizhou, Fujian and some other provinces of China [1]. It is quite different from existing tea resources due to its ultra-bitter taste. There are several known reasons that could be attributed to such bitterness, such as abundance in purine alkaloids, flavonoids, anthocyanins, or saponins [2]. Theacrine (1,3,7,9-tetramethyluric acid) is an alkaloid compound accompany with bioactive functions such as anti-depression, sedation, hypnosis, lipid metabolism regulation, etc. It is the second richest purine alkaloid in bitter tea [4]. 9-N-methyltransferase (CKTCS) was identified as being involved in synthesis process of theacrine by transcriptome sequencing of N-methyltransferase in Pu’er (Camellia sinensis var. assamica) and kucha [13]
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