The transcription of DNA, during which the genetic information carried by the DNA is copied and amplified in the form of messenger RNA (mRNA), is an essential cellular mechanism – its regulation alone involves no less than 5 to 6% of the genes!
Previously, this process was primarily observed in isolated and fixed animal cells using state-of-the-art techniques. The Biam researchers have now succeeded in imaging transcription, and in any cell of a plant. This will greatly facilitate the study of the adaptation mechanisms of plants in response to changes in their environment!
For example, whereas previously used conventional techniques, such as quantitative PCR, suggested that plants could respond within 20 minutes to phosphate nutrient input, the results from Biam show that the plant actually responds in only 3 to 5 minutes.
The results also reveal something totally unexpected: transcriptional heterogeneity within populations of cells with apparently identical functions.
How do the scientists manage to visualize molecules that are only 10 to 500 nm in size? By using a technique developed by one of the co-authors (from the CNRS's Institute of Human Genetics in Montpellier), which involves a viral protein fused to a fluorescent marker. This protein recognizes a specific RNA sequence that was introduced into the targeted gene. When the DNA of this gene is transcribed into mRNA, no less than 256 fluorescent proteins aggregate almost instantaneously with the produced mRNA, allowing the "live" observation of the DNA transcription zones in the nucleus of the cells.
In addition, recent microfluidic techniques make it possible to finely control the nutrient supply to the plant without disturbing the microscopy observations. The microscope slide is covered with a polymeric layer comprising small channels that are optimized for root feeding and growth, while limiting their movement as much as possible.
Finally, high-resolution, high-speed imaging was used to acquire 200 images in a few seconds. This gave the researchers access to all the cellular layers of the root and allowed them to follow in real time the changes that occur when a plant receives phosphate.
This work was performed in collaboration with the CNRS, the CEA-Irig, the Universities of Perpignan and Montpellier, the Pasteur Institute, La Trobe University (Australia), and the company TIMAC AGRO (St-Malo).
Visualizing transcription with unprecedented resolution:
The transcription "movies" can be seen by clicking on the link to the scientific publication.