Transcription plays a key role in cells by copying and amplifying the information carried by the genetic material (DNA), in the form of messenger RNA (mRNA). Its study is crucial to understand the functioning of living organisms. Indeed, in both animals and plants, 5 to 6% of genes are involved in the regulation of this phenomenon, clearly illustrating its biological importance.
Discovered in 1961, mRNA transcription was until now mainly observed on isolated and fixed animal cells, thanks to advanced techniques developed for many years by a team from the Montpellier Human Gene Institute (CNRS-University of Montpellier). The absence of movement in plants has finally made it possible to move to a new scale of complexity for all the cells of a living organism. Indeed, a team from the Institute of Biosciences and Biotechnologies of Aix-Marseille (BIAM CEA-CNRS-AMU) ^[1] has succeeded in observing and filming in real time the transcription of mRNA in all the cells of a plant.
This work now facilitates the deciphering of the mechanisms of numerous phenomena controlling the development and adaptation of plants in response to the constraints of their environment.
For example, conventional techniques previously showed that plants responded in less than 20 minutes to phosphate inputs (one of their main nutrients). The use of these new approaches has shown that it actually takes only 3 to 5 minutes for the plant to respond to variations in its nutrient environment.
In addition, these analyses also revealed significant transcriptional heterogeneity between cells that are supposed to perform identical functions: a reality that scientists were far from suspecting!

How does that work?
In order to visualize mRNA molecules (i.e. objects from 10 to 500 nm), the scientists exploited the expression of a viral protein fused to a fluorescent marker. This protein recognizes a specific RNA sequence introduced in the targeted gene of the plant in the gene they wish to study. When the latter is transcribed into RNA, it aggregates 256 fluorescent proteins on the mRNA produced. This system allows to directly observe the DNA transcription areas within the cell nucleus.

A technical exploit
Plants prove to be an excellent experimental material for the study of cells: unlike animal organisms, they are easily immobilized.
Recent technologies such as microfluidics allow the fine control of plant nutrition, while being compatible with microscopic observations. To do this, a polymer is coated on a microscope slide. It integrates fine channels to allow the growth and the feeding of the roots while limiting their movement to the maximum.
The BIAM team combined this tool with high-resolution, high-speed imaging, allowing the acquisition of 200 images in a few seconds. This allowed them to access all the cellular layers of the root and to follow in real time the changes that occur when a plant is fed with phosphate.