How transactivation works

Transactivation operates from a transcriptional "enhancer" (actually, this could be involved in up-regulation or down-regulation in different contexts) and at least two cassettes containing the following component sequences: in one, a transcription activator (transactivator), and in the other(s), an upstream activation sequence (UAS), a minimal promoter that normally drives no transcription, and at least one gene whose expression is of interest, which can be a reporter gene or trait gene.

Transactivation vectors are inserted into the plant of interest via any method, such as TransBacter™. When the activator is expressed, it releases a DNA-binding molecule. The UAS serves as a binding site for the binding molecule released by the transactivator cassette, and may induce or suppress the expression of the adjacent gene.

The UAS and minimal promoter may be linked to any one gene or more than one gene. If there are multiple genes in the genome that are linked to UAS::minimal promoter cassettes, the act of binding to the UAS induces or represses them in parallel. When a reporter gene is linked to the minimal promoter and UAS, its expression can be used to monitor the expression of the transactivation sequence (1). However, the transcription factor molecule binds to any copy in the genome of the UAS (2), with no requirement that it be linked to the UAS.

Thus the expression by the reporter gene is initially useful to allow a researcher to determine the locations and developmental stages of transcription factor expression within the plant, and when work on a pathway is done, as an internal standard to measure the expression of other such genes with less readily detectable phenotypes.

The transactivation sequence can be introduced into the plant at the same time and on the same construct as a UAS/minimal promoter sequence (as shown above), but most effectively for pathway manipulation the two cassettes can be inserted into the genome separately. One method of doing this is described in our patent application WO 01/21781. For more detail, see the related page Using Transactivation Lines.

Choices about the method will depend on what genes or characteristics the researcher is trying to express. For example, we are currently interested in improving the system for work with bioindicators (sentinel plants).

All constructs are available under a Plant Enabling Technologies BiOS License and the associated BiOS Technology Support Agreement or a BiOS compliant MTA (contact us for more information).

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