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Biological Chemistry

Stressed Plants Destroy Damaged Chloroplasts

Plant Biology: A ubiquitin ligase prompts cells to destroy organelles that govern photosynthesis

by Judith Lavelle
October 26, 2015 | A version of this story appeared in Volume 93, Issue 42

Credit: Salk Institute
This TEM image reveals a damaged chloroplast (white arrow) with its contents leaking out.
A damaged chloroplast is degraded in a micrograph of Arabidopsis thaliana cells.
Credit: Salk Institute
This TEM image reveals a damaged chloroplast (white arrow) with its contents leaking out.

In stressful conditions such as drought and high temperature, a plant cell’s chloroplasts can become damaged and produce harmful reactive oxygen species (ROS). Researchers at the Salk Institute have uncovered that plants produce an enzyme to signal cells to degrade ROS-producing chloroplasts before they do too much damage (Science 2015, DOI: 10.1126/science.aac7444). The team led by Jesse D. Woodson and Joanne Chory first created a strain of Arabidopsis thaliana sensitive to photooxidative stress. With transmission electron microscopy the researchers observed cells degrading damaged chloroplasts, which leak out their contents. With these green organelles destroyed, young plants never became green. The researchers then bred a second mutant plant that also underwent photooxidative stress but did turn green, indicating that chloroplasts were damaged but not destroyed. A genetic screen of these plants revealed a mutation disabling an enzyme called plant U-box 4 E3 ubiquitin ligase, suggesting that chloroplast degradation depends on that enzyme acting as a stress signal. Understanding this mechanism may help scientists create better drought- or temperature-resistant plants.


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