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Title: TISSUE DIFFERENTIAL EXPRESSION OF LYCOPENE BETA-CYCLASE GENE IN PAPAYA

Author
item SKELTON, RACHEL - HARC
item YU, QUINGYI - HARC
item SCRINIVASAN, RAJESWARI - UNIV HAWAII
item MANSHARDT, RICHARD - UNIV HAWAII
item Moore, Paul
item MING, RAY - U ILLINOIS/ HARC

Submitted to: Cell Research
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 2/15/2006
Publication Date: 8/1/2006
Citation: Skelton, R.L., Yu, Q., Scrinivasan, R., Manshardt, R., Moore, P.H., Ming, R. 2006. Tissue differential expression of lycopene beta-cyclase gene in papaya. Cell Research. p.731-739.

Interpretive Summary: Non-green pigments in flowers and fruits are distinct features primarily related to light absorption and protection of the green photosynthetic pigment chlorophyll against damage due to high intensity light. Non-green pigments may also result in variously colored flowers and fruit where the specific color pattern may provide fitness advantages such as attracting insects for pollination and birds for seed dispersal. Papaya fruit is generally the yellow color of carotenoids but it may also be the red color of lycopene. Since carotenoids are the source of human vitamin A, and lycopenes are antioxidants that help prevent cancers, there are nutritional and health implications tied to the color of papaya fruit flesh. Collaborative research in Hawaii among the U.S. Pacific Basin Agricultural Research Center, the Hawaii Agricultural Research Center, the University of Hawaii, and the University of Illinois isolated and characterized a key gene regulating the carotenoid biosynthetic pathway. This work has potential to improve the nutritional quality of papaya and will be used for understanding the genetic linkage between fruit color and fruit flesh firmness.

Technical Abstract: To elucidate the carotenoid biosynthesis pathway in papaya, we took a candidate gene approach to clone the lycopene beta-cyclase genes, LCY-B. A papaya LCY-B ortholog, cpLCY-B, was successfully identified from both cDNA and bacterial artificial chromosome (BAC) libraries and complete genomic sequence was obtained from the positive BAC including the promoter region. This cpLCY-B shared 80% amino acid identity with citrus LCY-B. However, full genomic sequences from both yellow- and red-fleshed papaya were identical. Quantitative real time PCR (qPCR) revealed similar levels of expression at six different maturing stages of fruits for both yellow and red-fleshed genotypes. Further expression analyses of cpLCY-B showed that its expression levels were 7 and 3 fold higher in leaves and flowers than in fruits, suggesting that cpLCY-B is down-regulated during the fruit ripening process.