Plants have molecules called “Tipp-Ex proteins” that can make corrective modifications to gene copies in chloroplasts and mitochondria. A study by the University of Bonn has revealed that these proteins are only allowed to work in these organelles to avoid fatal consequences for the cell. Chloroplasts and mitochondria have their own genes that provide instructions for key molecules needed for their functions. Defective genes in these organelles require correction to ensure the proteins assembled based on their instructions work properly. Tipp-Ex proteins, specifically pentatricopeptide repeat (PPR) proteins, are responsible for correcting these defects.
Plants have multiple PPR proteins, each specializing in correcting specific defects in gene copies. Even though these molecules are manufactured outside of the organelles, they only perform corrections within chloroplasts and mitochondria, not in the cytosol where gene copies from the cell nucleus are stored. Researchers investigated why these proteins are restricted to organelles and found that flooding the cytosol with excessive PPR proteins caused them to modify correct gene copies. This highlights the risk of interfering with protein functions through incorrect corrections, emphasizing the importance of tightly regulating PPR protein production.
The transportation mechanism of PPR proteins from the cytosol into organelles is controlled to prevent incorrect corrections. By limiting the quantity of PPR proteins produced and ensuring they are promptly transported into the organelles, plants can prevent unnecessary modifications in the cytosol. PPR proteins also recognize off-target sequences that resemble defective sequences but are actually correct. With numerous gene copies in the cytosol, the risk of incorrectly correcting these sequences is high, underscoring the necessity of strict regulation to avoid detrimental effects on protein function.
The findings of this study enhance understanding of how corrective proteins target gene copies in chloroplasts and mitochondria. By identifying the mechanisms that regulate PPR protein action, future research may leverage these insights to make targeted modifications to specific gene copies within organelles. This could have significant implications for exploring the impact of such modifications on plant energy metabolism given the crucial roles of chloroplasts and mitochondria. The study was funded by the German Research Foundation (DFG), supporting advancements in plant biology research and potential practical applications of the findings.
