For comprehensive evaluation of the taste quality of Pu’an black tea, the taste characteristics of black teas made from Camellia tetracocca Zhang (SQ) and Yunnan large-leaf cultivars (YD) in Pu’an county, Guizhou province were evaluated by sensory evaluation, quantitative taste assessment and chemical composition analysis combined with taste activity value (TAV) analysis and multivariate statistics, and taste contributors and differential taste compounds among different types of Pu’an black tea were identified. The results showed that Pu’an black tea had a sweet, mellow and strong taste. SQ had stronger sweetness and mellowness, while YD presented a more intense taste. SQ showed significantly lower contents of caffeine, theaflavins, thearubigins, and theabrownin but significantly higher soluble sugar contents compared with YD. The TAV of theanine and glutamic acid, two amino acids that contributed the most to the taste, were much greater than 1. Correlation analysis showed that cysteine was the major sweet amino acid. Tea polyphenols, caffeine, theaflavins, and histidine were the major sources of bitterness and astringency in tea soup. Orthogonal partial least squares-discriminant analysis (OPLS-DA) identified 11 differential taste components between SQ and YD, including leucine, serine, caffeine, threonine, isoleucine, lysine, arginine, valine, cysteine, glutamic acid and thearubigins. Principal component analysis (PCA) based on 26 taste components revealed that the mean value of comprehensive scores for taste quality of different types of Pu’an black tea decreased in the following order: SQ2 (1.15) > YD0 (0.23) > YD1 (−0.44) > YD2 (−0.83). It was found that Pu’an black tea produced from one bud and two tender leaves of C. tetracocca Zhang exhibited the best taste quality. This finding provides a reference for the development of Pu’an’s black tea industry.

Caffeine (CAF), a primary flavor component in tea, is one of the main reasons for the popularity of tea beverages. As an important secondary metabolite in tea plants, the CAF content varied greatly among different tea accessions. However, the genetic mechanisms underlying the CAF biosynthesis were still unclear. In this study, we performed a genome-wide association study (GWAS) on 359 tea accessions in the Guizhou Plateau to identify genetic variation associated with CAF content. A total of 19 significant single nucleotide polymorphisms (SNPs) and key gene (CsAK) involved in CAF biosynthesis were identified. Subcellular localization revealed that the CsAK-GFP fusion protein was located on the cell membrane. Antisense oligodeoxynucleotide (AsODN) targeting the CsAK gene to the buds and leaves revealed that the expression levels of the CsAK gene were significantly reduced, and the corresponding CAF content was also decreased in AsODN-treated tea plants. Overexpression of the CsAK gene in eukaryotic cells resulted in the accumulation of key intermediate product (L-methionine) during CAF biosynthesis process. These findings offered a theoretical foundation for future tea breeding programs aimed at cultivating excellent germplasm with high or low levels of CAF.