Submitted to: Plant and Animal Genome Conference Proceedings
Publication Type: Abstract Only
Publication Acceptance Date: 10/5/2005
Publication Date: 1/12/2006
Citation: Ostroff, R.L., Yu, Q., Srinivasan, R., Manshardt, R., Moore, P.H., Ming, R. 2006. The Expression Of The Gene For Lycopene B-Cyclase Is Elevated In Leaves And Flowers And Down-Regulated In Both Yellow- And Red- Fleshed Papaya Fruits. Plant and Animal Genome XIV International Conference Proceedings. P479, Pg. 221.
Technical Abstract: Carotene pigments in flowers and fruits are distinct features related to fitness advantages such as attracting insects for pollination and birds for seeds disposal. In papaya, the flesh color of fruit is considered a quality trait that varies in nutritional values and is linked to shelf life of the fruit. To elucidate the carotenoid biosynthesis pathway in papaya, we took a candidate gene approach to clone the lycopene '-cyclase genes, LCY-B and CYC-B. Degenerate primers were designed from conserved regions of these two genes from multiple species to amplify the target gene using papaya genomic DNA as a template. The 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 identify 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 three different maturing stages of fruits for both yellow and red-fleshed genotypes. Further expression analyses of cpLCY-B showed that its expression levels were 16 and 13 folds higher in leaves and flowers than in fruits, suggesting that cpLCY-B is down-regulated during the fruit ripening process. Degenerate primers from CYC-B yielded no product, suggesting there is no CYC-B ortholog in papaya. The yellow flesh of papaya fruit is likely caused by a novel lycopene '-cyclase that completely converts lycopene to '-carotene.