Abstract
In this paper, we selected transgenic birch (Betula platyphylla Suk) plants, which included non-silencing plants, transcriptional silence plants including TP96, TP74, TP73 and the post-transcriptional silence ones (TP67 and TP72). The transcription of the bgt gene in different tissues and organs were significantly different. The transcriptional level of bgt gene in the different tissues and organs was in the following order: leaf > female flower and male flower > branch bark > phloem > root.The transgenic lines were monitored for foreign gene expression for a long-term period of 8 years during their continuous growth under field conditions. GUS protein expression was not reactivated in the transgene silencing lines TP72 and TP67 when cultured in field conditions for long-term period. Meanwhile, no cases of gene silencing were observed again during the study period in the field conditions. Our results suggest that transgene expression in transgenic birch plants appears to be stable under field conditions. The frequencies of methylated cytosines in the code regions of gus gene was studied. Relation of transgene expression and DNA methylation was analysed. The data of restriction enzyme digestion (HpaII andMspI) indicated that DNA methylation resulted in post transcriptional gene silencing (PTGS) in transgenic birch. Key words: Transgenic birch, DNA methylation, gene silencing.
Highlights
Genetic transformation of woody plants is a promising tool for their genetic improvement, since their breeding has limitations imposed in general by their high heterozygosity, long juvenile periods and auto incompatibility (Tang et al, 2007)
The transcriptional level of bgt gene in the different tissues and organs was in the following order: leaf > female flower and male flower > branch bark > phloem > root
Our results suggest that transgene expression in transgenic birch plants appears to be stable under field conditions
Summary
Genetic transformation of woody plants is a promising tool for their genetic improvement, since their breeding has limitations imposed in general by their high heterozygosity, long juvenile periods and auto incompatibility (Tang et al, 2007). In recent years, inserting foreign DNA into plants expressing insect resistance is a new way to accelerate woody plant breeding. The development of transgenic insect-resistant plants provides a quick and safe approach to pest management. Stable expression of foreign gene is important for commercial use of genetic transformation in long-lived tree species as well as for ecological risk-assessment studies. 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)
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