Abstract: Carotene, participating in photosynthesis and protecting photosynthetic system, is one of the important pigments of tea leaves. Two key genes [lycopene β-cyclase gene (CsLCYb) and lycopene ε-cyclase gene (CsLCYe)] of carotene biosynthesis in tea plant were cloned from transcriptome. They are 1 515 bp and 1 524 bp in length, and encode 504 and 507 amino acid residues, respectively. Based on sequences alignment, CsLCYb and CsLCYe are highly conserved as compared with the homologous genes from other plants. Multiple-gene tandem expression indicated that CsLCYb can cyclize lycopene to β-carotene while CsLCYe was inactive. The enzymatic activities of the two genes were further confirmed by ELISA method in E. coli. It showed that CsLCYb was able to generate a large amount of carotene, which was significantly different from the negative control. However, no carotene was detected in the colonies with the expression plasmid of pAC-LYC-CsLCYe. The type and content of carotene in tea foliage were consistent with previous reports, which proved that carotene was mainly produced by the LCYb pathway in tea plant. The qRT-PCR analysis revealed that the expression level of CsLCYb in buds and different leaves of Zhonghuang 2 was positively correlated with the degree of chlorisis and the content of carotene. Furthermore, its relative expression in normal cultivar Longjing 43 and chlorisis cultivar Zhonghuang 2 also showed similar pattern. These findings confirmed that CsLCYb plays a key role in the carotene biosynthesis and leaf color changing in tea plant, which also provided an important genetic basis for uncovering the molecular mechanism of chlorisis in tea cultivars.

Key words: tea plant, lycopene cyclase, carotene, gene expression, chlorisis cultivars