Submitted to: Transgenic Research
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 1/19/2008
Publication Date: 2/7/2008
Citation: Flores, T., Karpova, O., Su, X., Zeng, P., Bilyeu, K.D., Sleper, D.A., Nguyen, H.T., Zhang, Z.J. 2008. Silencing of Gm FAD3 gene by siRNA leads to low a-linolenic acids (18:3) of fad3 -mutant phenotype in soybean [(Glycine max (Merr.)]. Transgenic Research. Available: http://springerlink.com/content/432379137526k10x/?p=ae33e422efb94387b5899d4f6e577a23&pi=29. Interpretive Summary: Biotechnology offers a variety of tools to manipulate expression of genes and activities of enzymes in plants to provide the means to produce more nutritious foods and feeds. More research is required to fully understand the mechanisms by which the activity of plant genes can be reduced to achieve a desired trait. One way to do this is to use the natural regulatory pathway in plants that uses small double stranded RNA molecules to reduce the activity of a gene; the RNA interference machinery. The objective of this work was to utilize RNA interference in soybeans to down-regulate a fatty acid desaturase gene family to effect a reduction in linolenic acid in the seed oil. This research will not only provide us with the desired trait for soybean improvement but it is also designed to provide information that will allow us to better understand how to manipulate the plant RNA interference system. We demonstrated that down-regulation of the desaturase gene family appeared to involve a mechanism that was distinct from the RNA interference system that had previously been described for mammals. The impact of these results is the knowledge that unique mechanisms may operate in plants that affect the way the tools of biotechnology can be used to achieve value added traits in soybeans and plants in general.
Technical Abstract: RNA interference (RNAi) has been recently employed as a powerful experimental tool for both basic and applied biological studies in various organisms including plants. RNAi deploys small RNAs, either small interfering RNAs (siRNAs) or microRNAs (miRNAs), to mediate the degradation or translational repression of mRNA, two important processes for regulating gene expression. Of these two regulatory controls, only miRNA- but not siRNA-directed translational repression has been reported in plants. Here we show that silencing of the omega-3 fatty acid desaturase gene family by a siRNA-generating transgene might involve the translational repression of target transcripts in the homozygous transgenic soybean (Glycine max). Such putative repression was manifested by the GmFAD3 null-like phenotype in the presence of normal or even higher levels of target mRNA. We propose that the pathway of siRNA-mediated translational repression exists in plants and that such repression may involve a mechanism distinct from imperfect base-pairing, in contrast to mammalian model. Our results imply that the assessment of gene silencing based either on mRNA degradation or on phenotype analysis alone may overlook the potent down-regulation of target genes through siRNA-mediated translational repression.