Processing Pathway: The Waste Management Of Plant Mitochondria

Mitochondria are tiny bodies inside the cells of animals, plants, and fungi that were derived from an endosymbiotic process involving bacterial and archaeal cells. Despite their tiny size, mitochondria are essential for energy production, stress response, and other important biochemical pathways. These processes make them look like busy factories, but, just like any other factories, with bigger productions come bigger waste.

To do their regular activities, mitochondria mostly do not produce their own proteins. Most of them are synthesized outside the organelle and have to be imported inside with the help of a sorting signal that usually resides in the N-terminal targeting peptide. After precursor proteins are imported, a targeting peptide is cleaved by the processing peptidase and released into the mitochondrial matrix as by-products. As with any other waste, a free-targeting peptide could be dangerous if not handled properly.


In humans, the accumulation of free peptides has been associated with many diseases. An infamous example is the accumulation of amyloid beta-peptide, which causes Alzheimer’s disease. In plants, peptide accumulation was associated with disrupted organellar stability, as they can strongly interact and disrupt the lipid membrane. Free peptides can also disturb the protein import process, as they may bind to processing peptidases and trigger a premature stress response.

Mitochondria have evolved ways to manage this waste problem. One of the mechanisms that has been elucidated in great detail is the processing pathway, which was first fully characterized in plants.

Contrary to the proteasomal degradation in the cytosol, which is a straightforward degradation of ubiquitinated proteins or peptides by the proteasome, processing pathways require a stepwise degradation by multiple different peptidases. Long free targeting peptides are fragmented into oligopeptides by preprotein peptidase (PreP). Oligopeptides are then further degraded by organellar oligopeptidase (OOP) into short peptides. Finally, single amino acids are released from short peptides by aminopeptidases.

Figure. The processing pathway of protein import in plant mitochondria. Figure courtesy Abi Sofyan Ghifari.

Interestingly, this peptide-degrading mechanism is shared between mitochondria and another endosymbiotic organelle in plants, the chloroplast. Most of the peptidases involved in the processing pathway, such as PreP, OOP, and aminopeptidases, are dually-targeted, meaning that these peptidases are targeted and localized to both mitochondria and chloroplasts. Inactivation of these peptidases altered organellar stability and activity, which overall affects plant growth, development, and stress response.


As plants have hundreds of different proteases and peptidases, it is possible that other proteins may be involved in the process, which is essential for plant growth and response to environmental conditions.

Experimental findings and contributions on this area of research was highlighted in the article “The peptidases involved in plant mitochondrial protein import,” recently published in the Journal of Experimental Botany. This work was conducted by Abi S. Ghifari, Shaobai Huang, and Monika W. Murcha from the ARC Centre of Excellence in Plant Energy Biology, The University of Western Australia.



CCl4 Lewis Structure

A CCL4 Lewis structure is a diagram that represents the electron configuration of covalently bonded compounds. Lewis structures are meant to provide a […]

Are Ruby-Throated Hummingbirds Flying Across The Gulf Of Mexico?

Many people find it hard to believe that the small, backyard birds encountered during particular seasons travel thousands of kilometers […]

Malaria Risk May Increase In Tropical Regions Due To Climate Change

With wrong attitudes toward treatment in the face of inadequate/inaccessible preventive measures against malaria in the most highly-plagued countries, coupled […]

The Importance Of Physiology On Insect Geographical Distribution: The Role Of Desiccation Resistance For The Geographical Distribution Of Chagas Disease Vectors

Why do we not find polar bears in the tropics? Why are fewer insect species at higher latitudes (e.g., closer […]

Complex Polysaccharides In Immune Regulation

Published by Barbara Mulloy and Chris Rider Imperial College London, Department of Medicine and the National Institute for Biological Standards and […]

How Large Meteorite Impacts Affect Planetary Mantle Convection

Every now and then, car- or house-sized bodies entering Earth’s atmosphere from outer space meet a fiery end in a […]

“Where Did We Come From?” Using The Fossil Record To Find The True Ancestor Of The Homo Genus

One question that unites all members of the human race is, “Where did we come from?” Historically, we as a […]

Science Trends is a popular source of science news and education around the world. We cover everything from solar power cell technology to climate change to cancer research. We help hundreds of thousands of people every month learn about the world we live in and the latest scientific breakthroughs. Want to know more?