Stability of transgene expression in poplar: A model forest tree species

Abstract

-We evaluated the stability of trangene expression in a hybrid poplar (Populus tremula ´ P. alba) clone transformed with constructs carrying a reporter gene (uidA) under the control of either a constitutive (35S) or a vascular-specific promoter. Analyses of transgene expression by GUS fluorometry and histochemistry was performed on several hundreds of trees, originating from 44 different transgenic lines, grown under in vitro, greenhouse and field conditions. While important variations in expression levels occurred, the transgene appeared to be stably expressed throughout a 6-year period. Only one silenced transgenic line was detected under in vitro conditions: molecular analyses indicated that this line contained an elevated number of transgene copies and was probably silenced from the beginning, at the post-transcriptional level. Overall, these results suggest that transgene expression in perennial species such as trees remains stable over an extended period.

Transformation as a Tool for Genetic Analysis in Populus

“…In a study of 40 independent transgenic hybrid cottonwood (P. trichocarpa × P. deltoides) plants that expressed herbicide resistance and GUS reporter genes and were monitored for four years under field conditions, only one showed instability of the transgene expression (Meilan et al, 2002). Similar results were obtained in a study of 20 transgenic events that expressed the GUS reporter gene under 35S and xylem-specific promoters (Hawkins et al, 2003). In the same study stable transgene expression was found under in vitro, greenhouse and field conditions and the expression was not affected by stress treatments.…”

The stability of transgene expression and effect of DNA methylation on post transcriptional gene silencing (PTGS) in birch

“…However, analysis of the instable/stable transgene expression in tree is more problematic than in crop plants (kumer, 2000a). Several studies have been conducted in perennial plants, including poplar trees, over multiple seasons and after vegetative propagation (GalloMeagher and Irvine, 1996;Bettany et al, 1998;Cervera et al, 2000;Kumar and Fladung, 2001;Meilan et al, 2002;Hawkins et al, 2003;Leibbrandt and Snyman, 2003) but these studies have given conflicting result (Li, et al, 2008).…”

“…However, some studies did demonstrate that long term culture of transgenic plants in field affected the expression of the transgene (Kumar and Fladung, 2001;Hawkins et al, 2003). This is important in the application of transgenic tree species.…”

Wood production, wood technology, and biotechnological impacts

“…These are genomic regions, often located near the centromer of a chromosome, which are not expressed. However, field experiments with trees transformed with marker genes showed that, when the transgene is inserted as single copy in euchromatin regions, silencing was a rare event in the investigated poplars (Hawkins et al 2003, Fladung et al 2004). …”