Researchers have characterized genes and proteins that are involved in the splicing process in the mitochondria of plants and are essential for cellular respiration and growth
Mitochondria is an intracellular organelle that produces a significant part of the chemical energy (ATP) in cells and is required for their function and maintenance. One of the things that distinguish the mitochondria in plants compared to that of animals, is its genetic load. Unlike most organelles in the cell, mitochondria have independent DNA. The presumed origin of this DNA is in an ancient single-celled creature that developed a symbiosis (mutual relationship) with a cell of archaic origin (which may have already had a nucleus and organelles).
What is the question? How does the genetic system work and is controlled in the mitochondria of plants, which is essential for their development?
"Mitochondria in a plant have a complex genome system that serves as an important model for understanding control mechanisms of gene expression, also in other organisms, including humans. The expression of the mitochondrial genome in plants is very complex, especially at the RNA level (a molecule that transmits the genetic information needed to build proteins that are essential for cell function). In our research, we are trying to understand how and when the genes in plant mitochondria are expressed and under what circumstances expressions are controlled," explains Prof. Oren Osterzerzer-Biran from the Institute of Life Sciences at the Hebrew University of Jerusalem.
One of the essential processes for the expression of the mitochondrial genome in a plant (similar to the nuclear genome) is called splicing; In this process, RNA molecules coded directly from the DNA undergo processing where they are cut, so that certain segments (called introns) are removed from them. Thus, the remaining segments are joined together to form mature RNA molecules that encode the information needed to build proteins. If this process is damaged, the RNA molecules cannot fulfill their role.
Prof. Osterzerzer-Byrne says: "Through the characterization of mitochondrial splicing in plants, we learn about how it is done at the molecular level (information that is also relevant to very complex splicing systems that exist in the cell nuclei of plants, animals and humans), and about the evolution of this process in nature. In other words, the mitochondria in plants serves as a unique model for us to understand the control of genome expression. For, genes that include introns cannot function.
"In addition, if we deeply understand the mechanisms of splicing and the control of genome expression in plant mitochondria, we may be able to harness this information to develop genetic and biological tools for the benefit of man, in industry, agriculture and the environment. For example, we can optimally direct germination, growth and development of plants. Alternatively, we may be able to delay the development of harmful plants, for example those that compete with food crops in agricultural fields or algae that secrete toxins into drinking water."
In one of their latest studies, Prof. Osterzerzer-Byrne and his team sought to characterize genes and proteins that control mitochondrial splicing and determine their mechanism of action. "As mentioned, the mitochondria is a complex and well-controlled genetic system, but we still do not know how the control of genetic expression works in it at the molecular level. That's why we wanted to understand the mechanism by which genes work in the mitochondria - what is their exact role and how they perform it in splicing (removing the excess segments). In addition, we wanted to understand if they are essential for other processes in plants, such as control of the respiratory system. Mitochondria are also responsible for this process due to the production of cellular energy and it is of course essential for the development of plants. As with all organisms and in humans, if the breathing process is damaged, damage to many physiological systems is expected. Hence, it is very important to understand how the factors responsible for it work," explains Prof. Osterzerzer-Byrne.
As part of the research, which won a grant from the National Science Foundation, the researchers examined model plants such as white sedum, tobacco and tomato using molecular, genetic (DNA and RNA sequencing) and biochemical methods (reviewing the proteins and respiratory centers in the mitochondria). They grew the plants in controlled growth cells and followed their development - germination, growth, flowering and fruit formation. That is, the genes and proteins were monitored from the level of their expression to the level of the organelle and the effect on the physiology of the plant.
To characterize genes and proteins involved in mitochondrial splicing and determine their role, the researchers damaged them and then videotaped the splicing process going awry. This is how they discovered that the role of one of the proteins is expressed in its binding to a specific region in the RNA molecules. In this way, enzymes are recruited that remove the excess segments from the RNA and enable the formation of mature RNA molecules, which, as mentioned, encode the information needed to build proteins.
"We found a gene from which the protein formed binds to the end of the RNA molecules and thus determines the point where the transcription ends for the continuation of the splicing process. In the absence of this protein, the RNA molecule is completely digested by a cutting enzyme (exonuclease). That is, we were able to understand the mechanism by which the protein works and controls the stability of the RNA molecule and its further processing into a mature RNA molecule. In addition, we have characterized many other genes and proteins that are necessary in splicing, but we still do not know what exact role they play and continue to investigate this. But the very discoveries are of great importance in understanding the process and its significance in controlling genetic expression in plants, their respiration and development," explains Prof. Osterzerzer-Byrne.
In many cases, when the researchers damaged the expression of the protein in the mitochondria, they discovered that an excess of primary RA molecules was formed, and thus the translation of the genes into proteins was damaged and the assembly of the protein complexes in the mitochondrial membrane, which is essential for the production of cellular respiration, was damaged.
In many cases, when the researchers damaged the expression of the protein in the mitochondria, they discovered that an excess of primary RNA molecules (which are not processed correctly) was created, and thus the translation of the genes into proteins was damaged and the assembly of the protein complexes in the mitochondrial membrane, which is essential for the production of cellular respiration, was damaged. This is how the respiration process in plants was damaged - absorption of oxygen and emission of carbon dioxide - which led to the collapse of cells and damage to the development of the plants.
"It can be said that the research, which focuses on the characterization of splicing in plant mitochondria, contributes to the understanding of the control of gene expression in mitochondria, which also affects the construction of the respiratory system and development. We believe that these findings are valid for plants and all organisms", Prof. Osterzerzer-Byrne concludes.
Life itself:
Prof. Oren Osterzer-Byrne, 57, married + two children (25, 20), lives in Shoham. His two children were recruited in the "Iron Swords" war. He was also recruited into a regional alert team due to his military past. On good days he likes to build and repair mountain bikes and ride them.
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