Dynamic change of the carotenoid metabolic pathway profile during oolong tea processing with supplementary LED light.

Carotenoid-derived volatiles are important contributors to tea aroma quality. However, the profile of the carotenoid pathway and carotenoid-derived volatiles (CDVs) artificial regulation in oolong tea processing has yet to be investigated. In the present work, the content and varieties of carotenoid-derived volatiles, the genome-wide identification of carotenoid cleavage dioxygenase (CsCCD) gene family, the expression level of CsCCD and other key genes in the carotenoid pathway, and the profile of carotenoid substances were analyzed by multi-omics and bioinformatics methods with innovative postharvest supplementary LED light during oolong tea processing. The results showed that during oolong tea processing, a total of 17 CDVs were identified. The content of ß-ionone increased up to 26.07 times that of fresh leaves and its formation was significantly promoted with supplementary LED light from 0.54 µg/g to 0.83 µg/g in the third turning over treatment. A total of 11 CsCCD gene family members were identified and 119 light response cis-acting regulatory elements of CsCCD were found. However, the expression level of most genes in the carotenoid pathway including CsCCD were reduced due to mechanical stress. 'Huangdan' fresh tea leaves had a total of 1 430.46 µg/g 22 varieties of carotenoids, which mainly composed of lutein(78.10%), ß-carotene(8.24%) and zeaxanthin(8.18%). With supplementary LED light, the content of antherxanthin and zeaxanthin in xanthophyll cycle was regulated and CDVs such as α-ionone, ß-ionone, pseudoionone, damascenone, 6,10-dimethyl-5,9-undecadien-2-one, citral, geranyl acetate and α-farnesene were promoted significantly in different phases during oolong tea processing. Our results revealed the profile of the carotenoid metabolism pathway in oolong tea processing from the perspective of precursors, gene expression and products, and put forward an innovative way to improve CDVs by postharvest supplementary LED light.

Effects of turning over intensity on fatty acid metabolites in postharvest leaves of Tieguanyin oolong tea (Camellia sinensis).

Fatty acid derived volatiles (FADVs) are major contributors to the aroma quality of oolong tea (Camellia sinensis). Most of the processing time for oolong tea is taken up by turning over treatments, but the full profile of fatty acid metabolic changes during this process remains unclear. In this study, we detected fatty acids, their derived volatiles, and related genes of Tieguanyin oolong tea using biochemical and molecular biology methods. The results showed that with an increase in turning over intensities, the content of total unsaturated fatty acids continuously dropped and the content of characteristic FADVs, such as hexanoic acid (Z)-3-Hexenly ester and 2-exenal, continued to increase. Lipoxygenase (LOX), a key gene family in the fatty acid metabolic pathway, showed different patterns, and CsLOX1 (TEA025499.1) was considered to be a key gene during the turning over processes. We found that fruit-like aroma (Z)-3-Hexen-1-ol acetate had a strong correlation with the expression levels of eight Camelia sinensis LOX family genes. Tieguanyin had relatively rich pleasant volatile compounds with moderate turning over intensity (five times turning over treatments). This study provides an overall view of how fatty acid metabolites change and affect the quality of oolong tea with different turning over intensities during processing.

[Genome-wide identification of CsCCD gene family in tea plant (Camellia sinensis) and expression analysis of the oolong tea processing with supplementary LED light].

Carotenoid cleavage dioxygenase (CCD) family is important for production of volatile aromatic compounds and synthesis of plant hormones. To explore the biological functions and gene expression patterns of CsCCD gene family in tea plant, genome-wide identification of CsCCD gene family was performed. The gene structures, conserved motifs, chromosome locations, protein physicochemical properties, evolutionary characteristics, interaction network and cis-acting regulatory elements were predicted and analyzed. Real time-quantitative reverse transcription PCR (RT-qPCR) was used to detect the relative expression level of CsCCD gene family members under different leaf positions and light treatments during processing. A total of 11 CsCCD gene family members, each containing exons ranging from 1 to 11 and introns ranging from 0 to 10, were identified. The average number of amino acids and molecular weight were 519 aa and 57 643.35 Da, respectively. Phylogenetic analysis showed the CsCCD gene family was clustered into 5 major groups (CCD1, CCD4, CCD7, CCD8 and NCED). The CsCCD gene family mainly contained stress response elements, hormone response elements, light response elements and multi-factor response elements, and light response elements was the most abundant (142 elements). Expression analysis showed that the expression levels of CsCCD1 and CsCCD4 in elder leaves were higher than those in younger leaves and stems. With the increase of turning over times, the expression levels of CsCCD1 and CsCCD4 decreased, while supplementary LED light strongly promoted their expression levels in the early stage. The expression level of NCED in younger leaves was higher than that in elder leaves and stems on average, and the expression trend varied in the process of turning over. NCED3 first increased and then decreased, with an expression level 15 times higher than that in fresh leaves. In the late stage of turning over, supplementary LED light significantly promoted its gene expression. In conclusion, CsCCD gene family member expressions were regulated by mechanical force and light. These understandings may help to optimize tea processing techniques and improve tea quality.