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Summary A network of peptidases governs proteostasis in plant chloroplasts and mitochondria. This study reveals strong genetic and functional interactions in Arabidopsis between the chloroplast stromal CLP chaperone‐protease system and the PREP1,2 peptidases, which are dually localized to chloroplast stroma and the mitochondrial matrix.Higher order mutants defective in CLP or PREP proteins were generated and analyzed by quantitative proteomics and N‐terminal proteomics (terminal amine isotopic labeling of substrates (TAILS)).Strong synergistic interactions were observed between the CLP protease system (clpr1‐2,clpr2‐1,clpc1‐1,clpt1,clpt2)and both PREP homologs (prep1,prep2) resulting in embryo lethality or growth and developmental phenotypes. Synergistic interactions were observed even when only one of the PREP proteins was lacking, suggesting that PREP1 and PREP2 have divergent substrates. Proteome phenotypes were driven by the loss of CLP protease capacity, with little impact from the PREP peptidases. Chloroplast N‐terminal proteomesshowed that many nuclear encoded chloroplast proteins have alternatively processed N‐termini inprep1prep2,clpt1clpt2andprep1prep2clpt1clpt2.Loss of chloroplast protease capacity interferes with stromal processing peptidase (SPP) activity due to folding stress and low levels of accumulated cleaved cTP fragments. PREP1,2 proteolysis of cleaved cTPs is complemented by unknown proteases. A model for CLP and PREP activity within a hierarchical chloroplast proteolysis network is proposed.
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Intra-chloroplast proteases: A holistic network view of chloroplast proteolysis
Abstract Different proteases and peptidases are present within chloroplasts and nonphotosynthetic plastids to process precursor proteins and to degrade cleaved chloroplast transit peptides and damaged, misfolded, or otherwise unwanted proteins. Collectively, these proteases and peptidases form a proteolysis network, with complementary activities and hierarchies, and build-in redundancies. Furthermore, this network is distributed across the different intra-chloroplast compartments (lumen, thylakoid, stroma, envelope). The challenge is to determine the contributions of each peptidase (system) to this network in chloroplasts and nonphotosynthetic plastids. This will require an understanding of substrate recognition mechanisms, degrons, substrate, and product size limitations, as well as the capacity and degradation kinetics of each protease. Multiple extra-plastidial degradation pathways complement these intra-chloroplast proteases. This review summarizes our current understanding of these intra-chloroplast proteases in Arabidopsis and crop plants with an emphasis on considerations for building a qualitative and quantitative network view.
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- Award ID(s):
- 2322813
- PAR ID:
- 10539849
- Publisher / Repository:
- Oxford University Press
- Date Published:
- Journal Name:
- The Plant Cell
- Volume:
- 36
- Issue:
- 9
- ISSN:
- 1040-4651
- Format(s):
- Medium: X Size: p. 3116-3130
- Size(s):
- p. 3116-3130
- Sponsoring Org:
- National Science Foundation
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