Papaya genetically modified for random resistance to PRSV virus

Papaya (Carica papaya L.) originates from South America, and varieties are grown all over the world (Africa, Asia, Australia, Central America) where the climate is suitable. Papaya is best grown at temperatures from 20°C up to 30°C. Temperatures lower than 15°C will damage the development of the plant. Papaya can form fruits in its first year of life and the fruit can be picked and cooked as a vegetable before it is ripe as well as later when the fruit has become ripe. One of the most serious plant pests of papaya plants is a virus that is carried and infected by aphids that infect papaya plants. GMO papayas have been developed that are resistant to this virus. GMO papayas such as CUH-CP551-8, CUH-CP631-7, and UFL-X17CP-6 have introduced resistance to the plant virus PRSV (Papaya ringspot virus).

Papaya is often visited by thrips, moths, flies and mosquitoes which can contribute to pollination. Papaya is also visited by aphids (Aphis gossypii, A. craccivora and A maidis) which can carry infectious viruses that are harmful to papaya. Papaya ringspot virus (PRSV) is the plant pathogen that can cause the most damage to papaya. PRSV infection forms mosaic circles on the fruit and leads to reduced growth and fruit development. Entire orchards of papaya can become totally infected with PRSV within three to four months. Virus transmission occurs via aphids that have previously eaten on virus-infected plants. These pests extract nutrition with their proboscis (stinging beaks) from the sieve tubes in the leaves. The suction beak sticks into leaf veins, and will also be able to carry the virus (PRSV) with it in the phloem, which carries nutrition in water. These Aphis insects can thereby carry infection to other plants through feeding.

The genetic modification has been developed using a biolistic/particle gun on bacterial cultures. Then Agrobacterium tumefaciens with the developed genetic structure (plasmid pGA482GG/cpPRSV-4) with composite genes for Neomycin Phosphotransferase II (neo), Papaya Ringspot Virus Coat Protein (PRSV CP), Beta-Glucuronidase (uidA) is used to transfer the gene modification into in papaya germ cells. PRSV CP Coat protein (shell protein of virus) will bind together to form a shell for the virus which will complete their development in virus infected cells. This further development is prevented in genetically modified papaya with an inserted gene sequence for the protein PRSV CP, which produces RNA that will prevent successful virus development. It may be that this genetically modified RNA binds in whole or in part to the RNA in the virus shell from the virus and thereby prevents further development of the virus in the infected cells.

The fruit is eaten unripe as a vegetable in salad and prepared dishes. Treated unripe fruit is stored in cans with sugar syrup. Industry uses papaya to isolate papain. Papain is a protease enzyme found in high amounts in the green skin (latex) of unripe papaya. Ripe papaya fruit is used as fresh fruit sale to be eaten like melon. Fresh fruit is best kept in cold storage between 10 and 12°C. Ripening is promoted in papaya by storage temperatures between 18 and 25 °C and treatment with ethylene gas for 24 hours. It can also be stored in sugar as jam, jelly and marmalade. Papaya is also processed to be stored as puree, nectar, drink, powder, and baby food. Fresh fruit is also used by industry to make cosmetics. Papaya seeds can be pressed for oil. Producers can prevent the spread of genetically modified seeds by making oil from it. PSRV has been turned from a threat to the benefit of the papaya industry. The genetically modified papaya development will probably be a threat to small farmers.


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