The Ion Balance Influences The Efficiency Of Photosynthesis (Botany)

New role for ion transport proteins: As LMU biologist Hans-Henning Kunz shows, they are involved in gene regulation in chloroplasts.

Chloroplasts are the plants’ photosynthesis factories. They originally come from cyanobacteria that were “hijacked” by a host cell in the course of evolution and absorbed into the interior of the cell. Because of this history of origin, they are surrounded by a double envelope membrane and still have their own genome. Scientists led by Professor Hans-Henning Kunz from the LMU Biozentrum have now shown for the first time that ion transport proteins in the chloroplast membrane are involved in the regulation of these genes and thus play an important role in the control of photosynthesis.

An inner membrane in the chloroplast is the actual place of photosynthesis. However, it is surrounded by the inner envelope membrane, which, among other things, houses ion transport proteins that are responsible for regulating the ion balance in the so-called stroma. The stroma is the plasmatic basic substance inside the organelle, in which both the DNA of the chloroplast and its protein factories – the ribosomes – are located. For photosynthesis to proceed correctly, it is essential that the genes in the cell nucleus and in the chloroplasts work in a coordinated manner. “In the model plant Arabidopsis thaliana , we have now been able to demonstrate that the ion balance in the stroma influences this communication,” says Kunz.

The biologist had previously observed that chloroplast development is delayed and the plant takes care when the genes for two ion transport proteins are switched off. “Our experiments have now shown that helper proteins encoded in the cell nucleus without these ion transporters have difficulty binding their partner RNA in the chloroplast,” says Kunz. This prevents so-called RNA maturation, an important intermediate step in the transmission of the information contained in the chloroplast genes to the ribosomes. This defect was particularly pronounced in the RNA from which the ribosomes of the chloroplast are built. “Correspondingly, there are fewer functioning ribosomes, which severely impaired protein synthesis in the mutants,” says Kunz.

According to the scientists, their new findings can help protect photosynthesis more efficiently in difficult environmental conditions and thus better adapt crops to climate change. “Ion transporters could be an important tool here,” says Kunz. “Photosynthesis is very dependent on the biochemical environment in the stroma, and these transporters have a major influence on it. Only if we understand their complex functionality and structure in detail do we have the opportunity to manipulate them and make them usable. ”
The Plant Cell 2021

Featured image: Prof. Hans-Henning Kunz in the greenhouse. | © LMU

Reference: Rachael Ann DeTar, Rouhollah Barahimipour, Nikolay Manavski, Serena Schwenkert, Ricarda Höhner, Bettina Bölter, Takehito Inaba, Jörg Meurer, Reimo Zoschke, Hans-Henning Kunz, Loss of inner-envelope K+/H+ exchangers impairs plastid rRNA maturation and gene expression, The Plant Cell, 2021;, koab123,

Provided by LMU Munchen

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