Yun Sun

Tea aroma is a key indicator for evaluating tea quality. Although notable success in tea aroma improvement has been achieved with heterosis breeding technology, the molecular basis underlying heterosis remains largely unexplored. Thus, the present report studies the tea plant volatile heterosis using a high-throughput next-generation RNA-seq strategy and gas chromatography-mass spectrometry. Phenotypically, we found higher terpenoid volatile and green leaf volatile contents by gas chromatography-mass spectrometry in the F1 hybrids than in their parental lines. Volatile heterosis was obvious in both F1 hybrids. At the molecular level, the comparative transcriptomics analysis revealed that approximately 41% (9027 of 21,995) of the genes showed non-additive expression, whereas only 7.83% (1723 of 21,995) showed additive expression. Among the non-additive genes, 42.1% showed high parental dominance and 17.6% showed over-dominance. Among different expression genes with high parental dominance and over-dominance expression patterns, KEGG and GO analyses found that plant hormone signal transduction, tea plant physiological process related pathways and most pathways associated with tea tree volatiles were enriched. In addition, we identified multiple genes (CsDXS, CsAATC2, CsSPLA2, etc.) and transcription factors (CsMYB1, CsbHLH79, CsWRKY40, etc.) that played important roles in tea volatile heterosis. Based on transcriptome and metabolite profiling, we conclude that non-additive action plays a major role in tea volatile heterosis. Genes and transcription factors involved in tea volatiles showing over-dominance expression patterns can be considered candidate genes and provide novel clues for breeding high-volatile tea varieties.

Finished oolong tea products with distinctly characteristic cultivar aromas generally have higher economic value. To advance our understanding of the aromatic differences between Camellia sinensis cv. Tieguanyin (TGY) and Jinguanyin (JGY) cultivars and their underlying formation mechanism, volatile metabolomics analysis, electronic nose (EN) analysis, sensory evaluation, and RNA sequencing were performed during this study. The EN and sensorial analysis showed a significant difference in odour characteristics between the two cultivars, which featured sweet floral and fruity aromas and green floral aromas, respectively. A metabolomics analysis of tea products showed that linalool (floral, OAV = 50.6) and geraniol (rose-like and sweet, OAV = 1.9) may contribute to the characteristic aroma. The volatile determination at each stage during the oolong tea manufacturing process emphasized that the significant difference in linalool and geraniol contents in fresh leaves from the two cultivars and the increase rate were potential reasons for their characteristic aroma and suggested that the “Tanqing” treatment clarified and intensified the characteristic cultivar aroma. A linalool synthase CsLIN with the expected catalytic activity was identified by coexpression network analyses. Collectively, our work pinpoints two key aroma substances within two cultivars and elaborates on the potential cause of characteristic cultivar aroma formation.