Biochemical and molecular characterization of transgenic papaya (Carica papaya L. cv. Philippine solo) with delayed ripening trait

Papaya is a climacteric fruit and like other climacteric fruits in the tropics, one of its main problems is the significant post-harvest loss due uncontrolled ripening. One molecular strategy to control ripening is to down-regulate ethylene biosysnthesis through antisense expression of the ripening-related ACC synthase gene. This study reports the success of the first genetically modified crop-transgenic solo papaya with delayed ripening trait-developed in the country. Fifty-four putative transgenic lines were PCR-screened and confirmed for the presence of transgenes, the Kanamycin resistance marker and the antisense ACC synthase 2 gene using specific primers. The transgenes were also detected in the leaves, fruits and peduncles of the transgenic papaya trees, indicating the non-chimeric character of the transformed plants. On the basis of molecular analyses and desirable phenotypic traits, including delayed ripening trait, seven confirmed transgenic papaya plants from six unique lines were selected for subsequent relevant biochemical and proximate analysis. Southern blot analysis revealed a single insertion site and single copy of the ACC synthase 2 transgene in the genome of the selected transgenic papaya lines. In general, the selected transgenic papaya exhibited 1 to 2 days longer time to attain full yellow from color break to attain full yello from clor break and 6 to 7 days delayed tissue softening compared to control or nontransgenic papayas. Other than these, the proximate composition, TSS values, beta-carotene, ascorbic acid and benzyl isothiocyanate (BITC) content of the transgenic lines were comparable and substantially equivalent to nontransgenic solo papaya lines and proximate values reported for papaya cultivars. At 100% yellow stage, the proximate analysis of the fruits of the different lines and control papayas showed: 88.15-89.23% moisture, 0.602-0.709% protein, 0.797-0.880% crude fiber, 0.119-0.131% fat, 0.512-0.566% ash, and 9.653-10.57% carbohydrate. Beta carotene ranged from 500-769 micro g/100g while ascorbic acid ranged from 41.6-80.35 mg/100g. Free BITC ranged from 0.7-1.7 ppm. TSS or total sugars ranged from 10.1-14.2 deg B.