Regeneration and genetic engineering of a tropical tree, Azadirachta excelsa

Abstract

Azadirachta excelsa belongs to the family Meliaceae and is one of the most important silviculture trees in the tropics. In this study, we established a somatic embryogenesis system and succeeded in construction of transgenic lines expressing genes for Bar, GUS and GFP employing the Agrobacterium-mediated transformation technique. Somatic embryos were obtained after approximately two months of culture on Murashige-Skoog (MS) medium containing 5 μM 6-benzyladenine. Plantlets were then regenerated by transferring somatic embryos to modified 1/2 MS medium without phytohormones. We initially attempted genetic transformation using two different A. tumefaciens strains, and found only the strain LBA4404 to be active in infection to explants. The strain EHA101 was totally inactive, suggesting that a specific interaction between Agrobacterium sp. and host plant might be critical for gene transfer. The possibility is discussed of applying the methodology developed in this work to the practical propagation of tropical trees.