Alternative splicing regulates tea aroma quality formation during withering of fresh leaves

The flavor quality of tea, particularly its aroma, can be substantially enhanced by moderate withering of fresh leaves; however, this enhancement process cannot be attributed alone to the transcriptional regulation. Alternative splicing (AS) plays a key role as a post-transcriptional regulatory mechanism in regulating plant growth and development, stress response, and metabolism; however, it remains unclear whether AS is involved in tea aroma quality formation during the withering of fresh leaves. In this study, AS events of the expressed genes were systematically characterized based on the transcriptomic data from fresh leaves withered for different time intervals (0, 2, 4, 6, 8 and 10 h). A total of 88,976 AS events from 13,995 genes were identified. The highest number of differential alternative splicing (DAS) was found in samples after 4 h of withering and then gradually decreased; however, the number of DAS remained higher after 10 h of withering than after 2 h of withering. Furthermore, 25.1 % of the flavor-related genes and 40.1 % of the transcription factors underwent AS, and most of them were enriched in the hormone signaling pathway and the aroma volatile synthesis pathways. A total of 89 volatiles were identified from the withering samples. The relative contents of the volatiles increased with the increase in withering time and were significantly higher than those in the control sample after 4 h of withering. Compared to the expression of the normal transcripts, the expression of AS transcripts of most genes was more significantly correlated with the changes in the corresponding aroma content. These results suggest that AS was involved and played a key role in tea aroma quality formation during withering. Our results further revealed the complexity of tea flavor quality formation and provided new insights regarding its regulatory mechanisms.