Modifying Trees to Meet the Sustainability and Economic Challenges of Bioproducts Industry

Eucalyptus hybrids, especially the E. urophylla x E. grandis hybrid (E. urograndis), are grown widely in plantations due to their high productivity, lack of invasive characteristics, and excellent wood fiber quality and chemistry.  When E. urograndis is grown in tropical regions of Florida, it produces 8-15 dry tons per acre per year, depending on planting density and rotation age, and this productivity makes eucalyptus a very attractive lignocellulosic feedstock for the production of bioproducts.  Since this hybrid is sensitive to freezing temperatures, freeze tolerance was introduced by the insertion of the Arabidopsis C-Repeat Binding Factor (CBF2) gene by the Arabidopsis rd29a cold-inducible promoter.  In addition to the CBF2 gene, the freeze tolerant E. urograndis (AGEH427) contains a gene expression cassette (PrMC2-barnaseH102E) that prevents pollen development.    Pollen control addresses possible public concerns for transgene introgression into sexually compatible species via cross-pollination.  The PrMC2-barnaseH102E pollen control expression cassette was found to efficiently ablate pollen in tobacco, pine and eucalyptus and a complete pollen control phenotype was achieved in transgenic lines of eucalyptus and pine over multiple years, multiple test locations, and even when the PrMC2-barnaseH102E cassette was flanked by different genes.  The PrMC2-barnaseH102E transgenic pine and eucalyptus trees grew similarly to control trees in all observed attributes except the pollen-less phenotype.  The freeze tolerant AGEH427 line is currently being planted in small scale plantations in gulf coastal regions of the southeastern U.S. and is under review by the Biotechnology Regulatory Services of USDA/APHIS for deregulated status.