Ripening in papaya fruit is altered by ACC oxidase cosuppression.

Papaya (Carica papaya) is a very important crop in many tropical countries but it is highly susceptible to parasitic diseases, physiological disorders, mechanical damage and fruit overripening. Here we report a study on ACC oxidase cosuppression and its effects on papaya fruit ripening. Papaya ACC oxidase was isolated using PCR and embriogenic cells transformed by biolistic using the CaMV 35S promoter to drive the expression of the PCR fragment in sense orientation. Fifty transgenic lines were recovered and 20 of those were grown under field conditions. Southern analysis showed incorporation of the transgene in different copy numbers in the papaya genome. Fruits were evaluated in terms of texture (firmness), colour development, respiration and ethylene production. A sharp reduction in ethylene and CO2 production was detected, whereas softening and colour development of the peel were also altered. Overall, transgenic fruits showed a delay in ripening rate. A reduction in mRNA level for ACC oxidase in transgenic fruit was clearly detectable by northern blot. More studies are necessary before this technology can be used to extend the shelf life of papaya fruit.

Expression of a single-chain human interleukin-12 gene in transgenic tobacco plants and functional studies.

Interleukin 12 (IL-12) is a key heterodimeric cytokine produced by a variety of antigen-presenting cells, including dendritic cells, macrophages, and B cells. It displays a potent array of biological activities affecting natural killer (NK) and T cells. These activities include promotion of cell-mediated or type 1 T helper cell responses (Th1). Due to that property, IL-12 has been employed in cancer immunotherapy, in mouse models of infectious diseases and in airway inflammation, and it may also have utility as a vaccine adjuvant. Transgenic plants are being used in many laboratories around the world for the production of therapeutically valuable proteins and as vehicles for oral vaccines. Here we present the expression of a single-chain human interleukin-12 in transgenic tobacco plants. The biological activity of plant-produced IL-12 was determined by interferon gamma (IFN-gamma) production by natural killer (NK) cells, and the level of production was comparable to that obtained with commercially available recombinant IL-12. The potential use of this recombinant protein is discussed.