Adventitious bud regeneration and Agrobacterium tumefaciens-mediated genetic transformation of Eucalyptus urophylla × E. tereticornis interspecific hybrid.

A high-efficiency regeneration and genetic transformation system is indispensable for generating desirable traits in important trees such as Eucalyptus. However, lower regeneration efficiency is common for most varieties because of the recalcitrance of this genus. Here, a stable and highly efficient in vitro organogenesis protocol and Agrobacterium-mediated genetic transformation system of Eucalyptus were developed, and transgenic plants were obtained. In this protocol, the preferred explants were the top and middle stem internodes from in vitro micro-shoots of the E. urophylla × E. tereticornis hybrid. Modified Woody Plant Medium (mWPM) containing 0.025 mg·L-1 thidiazuron (TDZ) and 0.10 mg·L-1 indole-3-butyric acid (IBA) was used to induce multiple adventitious buds that allowed 85.6% shoot formation. The binary vector pBI121 carrying the neomycin phosphotransferase II (nptII) and β-glucuronidase (uidA) genes was applied for transformation. The preferred internodes were precultured for 0 to 3 d and infected with A. tumefaciens strain GV3101 grown to a bacterial density of 0.5 (OD600). Then, they were transferred to a co-culture medium supplemented with 50 μM acetosyringone (AS) and co-cultured for 2 d in the dark. The transgenic adventitious buds formed in regeneration medium, which was replaced by the same medium with a 2-wk subculture interval through kanamycin selection. Using the aforementioned method, transgenic plantlets can be obtained within 3 mo with a transformation frequency of 3.8%, which was verified by polymerase chain reaction amplification (PCR) and histochemical analysis of GUS activity. The constructed genetic transformation system will lay a foundation for mining gene functions and further molecular breeding of Eucalyptus. [ABSTRACT FROM AUTHOR]