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Updated: Mar 31, 2026

Assaying Proteasomal Degradation in a Cell-free System in Plants
Published on: March 26, 2014
Ubiquitin facilitates a quality-control pathway that removes damaged chloroplasts
Jesse D Woodson1, Matthew S Joens2, Andrew B Sinson3
1Plant Biology Laboratory, The Salk Institute, La Jolla, CA.
None:
Energy production by chloroplasts and mitochondria causes constant oxidative damage. A functioning photosynthetic cell requires quality-control mechanisms to turn over and degrade chloroplasts damaged by reactive oxygen species (ROS). Here, we generated a conditionally lethal Arabidopsis mutant that accumulated excess protoporphyrin IX in the chloroplast and produced singlet oxygen. Damaged chloroplasts were subsequently ubiquitinated and selectively degraded. A genetic screen identified the plant U-box 4 (PUB4) E3 ubiquitin ligase as being necessary for this process. pub4-6 mutants had defects in stress adaptation and longevity. Thus, we have identified a signal that leads to the targeted removal of ROS-overproducing chloroplasts.
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