Discovery of 'master switch' for the communication process between chloroplast and nuclei of plants
Scientists have been questioning for years how plants transmit stress signals due to water shortage or salinity from the chloroplast to the nucleus. They know that chloroplasts - the cellular organelles that give plants their green colour - have at least three different signals that can indicate that a plant is under stress.
Given the challenges the environment will face in the coming decades due to global warming, this piece of the puzzle has become more pressing for phyto-scientists, who hope that understanding plant stress reactions will ultimately lead to new generations of plants that are, among other things, more resistant to drought and stress.
That's why a study published this week in the internationally renowned journal Science is considered an important step in understanding how chloroplasts communicate with the nucleus of a cell when stresses such as drought, heat, salinity or light become too important for the body.
A research team composed of Shai Koussevitzky, an associate researcher at the University of Nevada, Reno College of Agriculture, Biotechnology and Natural Resources, and Ron Mittler, an associate professor of biochemistry and molecular biology, determined that multiple plant distress signals converge on a single pathway, which then channels information to the nucleus. The study is part of a collaboration led by Joanne Chory, Professor and Director of the Plant Biology Laboratory at the Salk Institute for Biological Studies in La Jolla, California, and a researcher at Howard Hughes Medical Institute.
Koussevitzky, looking at the end of the signalling pathway, found the corresponding binding factor known as ABI4, a known plant transcription factor. It prevents light-induced regulatory factors from activating gene expression. Further work in the project has established that the GUN1 protein, located in a chloroplast and nuclear coded, is required to integrate multiple stress derived signals into the chloroplast. This work was carried out by the first co-author of the article, Ajit Nott, who was a research associate in Dr. Chory's laboratory.
Many of the nuclear genes that encode chloroplast proteins are regulated by a "main switch" in response to environmental conditions. This "main switch", like a binary computer, can activate or deactivate certain gene sets depending on the stress signaling processes.
One of our suggestions in the paper is that ABI4 seems to be a prime candidate to be the "main switch," Koussevitzky said. "ABI4 binds to a newly identified sequence pattern and, in doing so, prevents light-induced regulatory factors from activating gene expression. It has a role in so many signalling processes in the plant, it may be the "main switch" that researchers are looking for."
These discoveries are crucial to future research efforts in the design of new generations of plants, Mittler said.
"Many things that happen in chloroplast are important for production, growth and environmental response," he says. "It is therefore a very basic communication mechanism between the chloroplast and the nucleus. It had already been suggested that the elements of this process should take multiple paths. This work shows that the elements do indeed pass through this particular path.
"Today, we are in a much better position to resolve the issue of producing plants that can use marginal water or marginal soil in a way that will not completely suppress the plant's normal metabolism and activate all its stress metabolism when it is under severe stress. If you want to generate a more tolerant plant, you have to take care of both of these things."
Added Koussevitzky: "We are trying to place the signalling lanes in the context of the plant's stress response. A little more adjustment will be needed, but knowing at least that it is going through a particular route will allow researchers to design what the targets should be downstream of those routes. The work carried out under this project was supported by a grant from the Ministry of Energy, the Howard Hughes Medical Institute, the long-term EMBO and the Howard Hughes Medical Institute scholarships.
Source: University of Nevada, Reno
