Transgene Containment in Forest Trees, 1997 Biological Sciences Symposium Proceedings

Key to commercial deployment of genetically engineered trees is the issue of transgene containment. Using poplars, our laboratory is addressing this issue from two perspectives. One approach is to develop methods to genetically engineer reproductive sterility. The second approach is to develop a risk assessment model to predict the rates and consequences of transgene escape from plantations. We have focused on floral homeotic genes as tools for genetic engineering of sterility. Four cDNAs and genomic clones homologous to genes that control floral development in model herbaceous species have been isolated from Populs trichocarpa: FLORICAULA /LEAFY (poplar homolog is PTFL), DEFICIENS/APETALA3 PTD), and AGAMOUS/PLENA (PTAG1 & 2). Based on the expression patterns of the poplar genes and the function of homologs, we are generating constructs for engineering reproductive sterility. These constructs employ either an altered floral homeotic cDNA to inhibit the activity of the endogenous gene or a floral homeotic promoter to drive expression of a cytotoxin, thereby ablating floral tissues. We are also investigating ways to produce early-flowering poplars via genetic and physiological methods to expedite analysis of sterility constructs. To inform risk assessments of transgene release, we are developing a spatial simulation model and measuring gene flow from wild and planted poplar stands. This model should allow predictions of the level of sterility required for transgene containment, and identify genes and environments where containment is most likely to be important.