Biological complexity: plant cell regulators (Introduction)

by David Turell , Monday, June 21, 2021, 20:49 (1034 days ago) @ David Turell

Newly defined:

https://phys.org/news/2021-06-universal-mechanism-cells.html

"All plant cells obtain their energy mainly from two organelles they contain—chloroplasts (responsible for photosynthesis) and mitochondria (responsible for the biochemical cycle of respiration that converts sugars into energy). However, a large number of a plant cell's genes in its mitochondria and chloroplasts can develop defects, jeopardizing their function. Nevertheless, plant cells evolved an amazing tool called the RNA editosome (a large protein complex) to repair these kinds of errors. It can modify defective messenger RNA that result from defective DNA by transforming (deamination) of certain mRNA nucleotides.

"Automatic error correction in plants was discovered about 30 years ago by a team headed by plant physiologist Axel Brennicke and two other groups simultaneously. This mechanism converts certain cytidine nucleotides in the messenger RNA into uridine in order to correct errors in the chloroplast DNA or mitochondrial DNA. RNA editing is therefore essential to processes such as photosynthesis and cellular respiration in plants. Years later, further studies showed that a group of proteins referred to as PPR proteins with DYW domains play a central role in plant RNA editing. These PPR proteins with DYW domains are transcribed in the cell nucleus and migrate through the cells to chloroplasts and mitochondria. However, they are inactive on their way to these organelles. Only once they are within the organelles do they become active and execute their function at a specific mRNA site. How this activation works, however, has been a mystery until now.

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"This three-dimensional architecture has actually provided the crucial clue to the mechanism of DYW domain activation that applies to all plants. It is due to a zinc atom located in the center of the DYW domain that can accelerate the deamination of cytidine to uridine like a catalyst. For this to happen, however, the zinc must be optimally positioned. The activation switch is provided by a very unusual gating domain in the immediate vicinity of the catalytic center—the structural analysis shows that this gating domain can assume two different positions, thereby switching the enzyme on or off. "The movement of the gating domain regulates the extent to which the zinc ion is available for the catalytic reaction," Weber explains.

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"Now it has become clear why getting DYW-type PPR proteins to react with RNA in the test tube has been difficult until now: These PPR proteins are nominally inactive and require activation. In the plant cells, they are first produced in the cell nucleus and then very likely migrate in an inactivated state to the organelles, where they become activated. "This is ideal, because otherwise these molecules would be active along the way, altering various RNA molecules in an uncontrolled fashion harmful to the cell," says Weber.

"This work is a breakthrough for plant molecular biology because it describes an additional level of sophisticated regulation in chloroplasts and mitochondria."

Comment: We have previously discussed God's error correction mechanisms. What is obvious is that they must be present when the plant is initially evolved. Chance evolution by chance mutation won't do that.