Research led by University of Pennsylvania biologists has identified small DNA sequences in plant that act as signposts for shutting off gene activity, directing the placement of proteins that silence gene expression. Manipulation of these short DNA fragments promises plants with enhanced activation of certain traits.

Doris Wagner, senior author on the study and a professor in Penn's Department of Biology in the School of Arts & Sciences said that in plants, the part of the genome that is not needed, or that might be providing exactly the wrong information, needs to be shut off reliably, and this information is passed on to daughter cells. The short sequences could then be manipulated using gene-editing techniques to alter gene expression.

The study focused on Polycomb repression, a form of gene regulation. Polycomb protein complexes were first discovered in fruit flies, and in plants and mammals later. These protein complexes play important roles in determining cell identity, and helping plant cells remember, for example, that they are leaf cells or flower cells. Professor Wagner's team examined the Polycomb complex called PRC2. The team identified 170 segments of DNA in the plant species Arabidopsis thaliana that were likely to be Polycomb response elements (PREs). Then they identified 55 transcription factors, and verified that 30 of them physically interacted with PRC2.

The researchers went back to the 170 PRE candidates and identified short DNA sequences called cis motifs, which are what transcription factors recognize when they scan the genome for their target genes. They found two cis motifs that matched up with two of the previously identified transcription factors. Putting the cis motifs in to a plant cell genome revealed they were sufficient for recruiting Polycomb, making them essentially a synthetic PRE.

For more details, read the article in PennNews

Figure: Researchers have identified small DNA "signposts" that direct the silencing of genetic activity, allowing plants to move through different stages of development. Left image of plants: Compared to normal Arabidopsis plants, plants with mutations in the Polycomb complex (two plants on right) have leaves that curl upward and flower early. The same is true for mutants in the 2 transcription factor families (TFs) that recruit Polycomb. Right image: Two transcription factors, BPC and ZnF, bind to the genetic motifs shown to recruit the Polycomb protein complex, which silences genes.