Potential for introducing cold tolerance into papaya by transformation with C-repeat binding factor (CBF) genes

Papaya (Carica papaya L.) production is affected by low temperatures that occur periodically in the subtropics. The C-repeat binding factor (CBF) gene family is known to induce the cold acclimation pathway in Arabidopsis thaliana. Embryogenic papaya cultures were induced from hypocotyls of “Sunrise Solo” zygotic embryos on semisolid induction medium. The CBF 1/CBF 3 genes along with the neomycin phosphotransferase (NPT II) gene were placed under the control of the CaMV 35 S promoter and introduced into a binary vector pGA 643. Embryogenic cultures were transformed with Agrobacterium strain GV 3101 harboring pGA 643. After selection of transformed embryogenic cultures for resistance to 300 mg l⁻¹ kanamycin, somatic embryo development was initiated and transgenic plants were regenerated. The presence of the CBF transgenes in regenerated plants was confirmed by Southern blot hybridization. The papaya and the related cold-tolerant Vasconcella genomes were probed for the presence of cold inducible sequences using polymerase chain reaction (PCR). Possible cold inducible sequences were present in the Vasconcella genome but were absent in the Carica genome.