Cloning Major Genes Controlling Fruit Flesh Color in Papaya
Ripe papaya fruit can be either red fleshed or yellow fleshed, which is largely determined by the concentrations of different carotenoid pigments. Higher lycopene content makes the fruit flesh red while higher β-carotene makes it yellow. Papaya flesh color has health implications in that it is indicative of levels of vitamin A and antioxidants. Yellow-fleshed papaya is a good source for vitamin A, while red fleshed has higher antioxidant properties. Papaya fruit flesh color segregates as a qualitative trait following Mendelian ratio with the yellow flesh being dominant over red, indicating that the trait is controlled by a single gene.
Cloning lycopene β-cyclase from red- and yellow-fleshed papaya revealed two copies of this gene acting independently in chloroplasts and chromoplasts. The CpLCY-B gene is expressed higher in chloroplast while CpCYC-b is expressed mainly in chromoplasts where it is responsible for β-carotene synthesis during fruit ripening. The CpLCY-B did not show any difference in expression in red- and yellow-fleshed varieties, discounting it having a role in fruit color development. The CpCYC-b is expressed higher in yellow-fleshed fruit than in red-fleshed fruit. Comparison of CpCYC-b sequences from red- and yellow-fruited varieties shows an insertion mutation in the red variety resulting in a truncated protein. This gene is located at a recombination hot spot near the telomere. Tightly linkage DNA markers were developed for marker-assisted selection of fruit flesh color in papaya.
KeywordsBacterial Artificial Chromosome Bacterial Artificial Chromosome Library Fruit Color Flesh Color Papaya Fruit
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