Researchers from the Department of Plant Sciences, University of Oxford, have discovered a new biochemical pathway in plants which they have named Chlorad. By manipulating the Chlorad pathway, the scientists can modify how plants respond to their environment. For example, the plant’s ability to tolerate stresses such as high salinity can be improved.
Oxford/UK — Chloroplasts are the organelles that define plants. Along with many other metabolic, developmental and signalling functions, chloroplasts are responsible for photosynthesis — the process whereby sunlight energy is harnessed to power the cellular activities of life. Consequently, chloroplasts are essential, not only for plants but also for the myriad ecosystems that depend on plants, and for agriculture.
Chloroplasts are composed of thousands of different proteins, most of which are made elsewhere in the cell and imported by the organelle. These proteins must all be very carefully regulated to ensure that the organelle keeps functioning properly. The Chlorad pathway works by removing and disposing of unnecessary or damaged chloroplast proteins; hence the name Chlorad, which stands for “chloroplast-associated protein degradation”.
Two decades on from the identification of the chloroplast protein import machinery — which delivers new proteins to chloroplasts — the discovery of the Chloard pathway reveals for the first time how individual, unwanted proteins are removed from chloroplasts. Previous studies showed that proteins in the chloroplast membranes are digested by a protein degradation system outside of chloroplasts. So, the key question was: How are chloroplast proteins extracted from the membrane to enable this to happen? The scientists discovery of the Chloard system answers this question, and they identified two novel proteins that act in the process.
Chloroplasts are eukaryotic organelles that originated more than a billion years ago from photosynthetic bacteria, by a process called endosymbiosis. The Chlorad system contains a mix of components of eukaryotic origin and bacterial origin. This provides an example of how eukaryotic host cells have evolved gradually, co-opting available tools in novel ways, to govern their endosymbiotic organelles.
The discovery of this biochemical pathway is a good example of how insights from fundamental plant biology research can reveal potential new strategies to develop crops that are more productive and resilient. This helps illustrate the value of basic science in contributing to addressing key global challenges including a rising global population, environmental stresses and an increased demand to deliver food security.
Developing stress-resistant crops that can have stable yields under stress conditions is an important strategy to ensure future food security. This need is particularly urgent considering the increased frequency of extreme weather conditions that accompany global climate change, which cause more severe environmental stresses, more frequent plant disease outbreaks, and reduced yield and harvest quality.