RESUMO
Oil palm, like all other crops, is susceptible to attack from several insect pests causing significant reduction in productivity. In the past, cry genes from Bacillus thuringiensis have been reported to be effective in conferring resistance towards insect pests in crops such as corn and rice. One of the advantages of these toxin proteins is their specificity towards certain harmful insects. A rapid and efficient method was developed for the transformation and evaluation of CryIA(b) expression in oil palm. A recombinant vector was introduced into immature embryos (IEs) of oil palm via the biolistic method. More than 700 putative transformed IEs from independent transformation events were generated. Transient transformation efficiency of 81-100 percent was achieved. We found that pre-treatment of target tissues with phytohormones is essential for increasing the transformation efficiency. This finding could enable higher transformation rate in oil palm that was previously difficult to transform. PCR analysis further confirmed the presence of the CryIA(b) in the transformed tissues. Expression of CryIA(b) from PCR-positive samples was further confirmed using a rapid gene expression detection system. This novel and rapid detection system could serve as a good opportunity to analyze the impact of transgenes upon transfer to the new environment, especially for crops with long generation cycle, such as oil palm.
RESUMO
Oil palm (Elaeis guineensis Jacq.) is the highest yielding oil-bearing crop. However, being a perennial crop, genetic improvement of oil palm is extremely slow. Indeed, compared to other annual oil crops such as soybean and rapeseed, genetic manipulations remained less important. Therefore, to remain competitive, oil palm growers and breeders need new and novel approaches. In this report, the potential of immature embryos (IE) as a useful tool for oil palm genetic transformation studies was evaluated. It was evident that IEs were amenable to both direct and Agrobacterium-mediated gene transfer. Due to the abundant supply of IE, optimization of biolistic and Agrobacterium-mediated gene transfer into IEs were easily carried out. Transient transformation frequencies were comparable to other plant systems reported, with as high as 97.4 percent recorded for biolistic and 64.4 percent for Agrobacterium-mediated gene transfer. Like most moncots, oil palm tissues were less sensitive to kanamycin, geneticin and chloramphenicol. Instead, both hygromycin and phosphinotrycin were toxic 20 mg/l, making both suitable candidates for selecting putative transformants. IEs were also more responsive to in vitro manipulations as compared to other explants such as leaf and root tissues. Rapid in vitro response to callusing and embryogenesis or rapid and highly efficient direct germination resulted in a shorter culture period. This would minimize the production of abnormal clonal palms, which has been associated to chromosomal aberration due to prolonged time in culture. In addition, IEs also allows rapid and direct introduction of elite genes into breeding programs and in biclonal seed production.