Chloroplast Proteolysis and Protein Quality Control in Plants

Chloroplasts maintain photosynthetic efficiency and stress resilience through tightly regulated proteolysis and protein quality control networks. Central to these systems are ATP‐dependent metalloproteases and molecular chaperones that recognise, refold or degrade misfolded and photodamaged proteins. Proteases such as FtsH and Deg family members collaborate in the photosystem II repair cycle by removing damaged D1 reaction‐centre proteins, while stromal Clp proteases and associated chaperone partners mediate broader turnover of stromal clients. Chaperones of the Hsp70 and Hsp100 families guide unstable proteins towards refolding or hand them over to proteases for degradation. Emerging evidence highlights interplay between proteolytic activity and retrograde signalling to the nucleus, ensuring coordinated biogenesis of chloroplast machineries. This balance of synthesis, repair and removal of proteins underpins chloroplast development, thylakoid membrane biogenesis and plant responses to environmental stress, with direct implications for crop improvement and sustainable agriculture.

Research from Nature Portfolio

A key study has defined a plastidial metalloprotease as a regulator of a small heat shock protein essential for thermomemory in Arabidopsis. In this work, loss of the metalloprotease led to sustained accumulation of the small heat shock protein after heat stress, enhancing acquired tolerance upon subsequent exposures. This discovery reveals a protease–chaperone control module that links targeted proteolysis to the maintenance of stress‐protective proteins, shedding light on how chloroplasts encode a molecular memory of thermal stress.

Chloroplast Proteolysis and Protein Quality Control in Plants publication trend

The graph below shows the total number of articles in chloroplast proteolysis and protein quality control in plants across all publications each year (not limited to Nature Index journals).

Technical terms

Proteolysis: The enzymatic cleavage of peptide bonds in proteins, leading to their degradation or processing.

Protease: An enzyme that catalyses proteolysis, often requiring ATP and metal ions for substrate recognition and turnover.

Chaperone: A protein that assists folding or refolding of nascent or stress‐damaged polypeptides, preventing aggregation.

Thylakoid membrane: Internal chloroplast membranes housing photosynthetic complexes and proteolytic machinery.

Photosystem II repair cycle: A quality control process in which damaged D1 proteins are selectively removed and replaced to restore photosynthetic activity.

Retrograde signalling: Communication from the chloroplast to the nucleus that adjusts nuclear gene expression in response to organelle status.

References

1. TurboID reveals the proxiomes of Chlamydomonas proteins involved in thylakoid biogenesis and stress response. Plant Physiology (2023).
2. FtsH Protease in the Thylakoid Membrane: Physiological Functions and the Regulation of Protease Activity. Frontiers in Plant Science (2018).
3. The plastid metalloprotease FtsH6 and small heat shock protein HSP21 jointly regulate thermomemory in Arabidopsis. Nature Communications (2016).
4. Specific Hsp100 Chaperones Determine the Fate of the First Enzyme of the Plastidial Isoprenoid Pathway for Either Refolding or Degradation by the Stromal Clp Protease in Arabidopsis. PLOS Genetics (2016).
5. Cooperative D1 Degradation in the Photosystem II Repair Mediated by Chloroplastic Proteases in Arabidopsis. Plant Physiology (2012).