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Progress in Research on Silencing Mechanism of Transgenic Tobacco


Progress in Research on Silencing Mechanism of Transgenic Tobacco Inquiry

The transgenic technology plays an important role in modern agricultural breeding. The silencing of transgenic genes is not conducive to the application of this technology. Therefore, this phenomenon is an important issue that transgenic workers need to consider. Among the tobacco materials obtained by researchers from the South China Botanical Garden of the Chinese Academy of Sciences, one-third of them have transgene silencing and cannot be used normally (Hou et al., 2014 Molecular Plant 7: 1756-1765). If the target gene can be re-expressed in these materials, the efficiency of this technology will be improved.

 

Previous studies have shown that many factors are related to gene silencing, such as the insertion position of the transgene in the genome, the number of copies of the transgene, the repetitive sequence, the homozygous heterozygous state of the transgene, and DNA methylation. Among the materials previously obtained by the research group, there is a tobacco strain that has successfully carried out two rounds of gene superposition but the transgene is silent (23.C.7). This strain has two copies of the transgene, one for site-directed integration (S) and the other for random insertion (R). Regardless of whether the S copy is homozygous or heterozygous, the target transgene is silent. DNA methylation analysis showed that the target transgene promoter was hypermethylated. Is it possible to activate the expression of the silent transgene by removing one of the copies?

 

 

To answer this question, researchers backcrossed the genetically modified material with wild-type tobacco and analyzed the gene expression of the offspring. Studies have found that gene silencing still exists in the offspring of some plants backcrossed, while in the offspring of some plants backcrossed, the expression of the transgene in the site-specific integration copy has been activated to varying degrees. Surprisingly, this activation phenomenon not only exists in plants with single-copy (S) but also in plants with the double-copy (RS).

 

Contrary to expectations, the activation of silent transgenes is not closely related to changes in copy number. DNA methylation data show that there is a significant difference in the degree of transgene methylation between the control strain with good gene expression and the gene silenced strain 23.C.7. Researchers try to find the answer from the perspective of DNA methylation. The results showed that there was no significant difference in the level and pattern of DNA hypermethylation among plants with different gene activation levels. Although DNA methylation is involved in gene silencing, DNA hypermethylation itself cannot “lock” the silent state.

 

In summary, this study shows that the gene silence state of transgenic plants can be activated to a certain extent through backcrossing, but the appearance of this phenomenon does not depend on the changes in transgene copy number and DNA hypermethylation. The activation mechanism needs to be further explored.

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