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Abstract The chloroplast chaperone CLPC1 aids to select, unfold, and deliver hundreds of proteins to the CLP protease for degradation. Through in vivo CLPC1, trapping we previously identified dozens of proteins that are (potential) substrate adaptors or substrates for the CLP chaperone–protease system. In this study, we show that two of these highly trapped proteins, DUF760-1 and DUF760-2, are substrates for the CLP protease in Arabidopsis (Arabidopsis thaliana). Loss-of-function mutants and transgenic plants were created for phenotyping, protein expression, and localization using immunoblotting and confocal microscopy. In planta BiFC, cycloheximide chase assays, and yeast 2-hybrid analyses were conducted to determine protein interactions and protein half-life. Both DUF760 proteins directly interacted with the N-domain of CLPC1 and both were highly enriched in clpc1-1 and clpr2-1 mutants. Accordingly, in vivo cycloheximide chase assays demonstrated that both DUF760 proteins are degraded by the CLP protease. The half-life of DUF760-1 was 4 to 6 h, whereas DUF760-2 was highly unstable and difficult to detect unless CLP proteolysis was inhibited. Null mutants for DUF760-1 and DUF760-2 showed weak but differential pigment phenotypes and differential sensitivity to protein translation inhibitors. This study demonstrates that DUF760-1 and DUF760-2 are substrates of the CLP chaperone–protease system and excellent candidates for the determination of CLP substrate degrons.
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The CLP and PREP protease systems coordinate maturation and degradation of the chloroplast proteome in Arabidopsis thaliana
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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- Award ID(s):
- 1940961
- PAR ID:
- 10392915
- Publisher / Repository:
- Wiley-Blackwell
- Date Published:
- Journal Name:
- New Phytologist
- Volume:
- 236
- Issue:
- 4
- ISSN:
- 0028-646X
- Page Range / eLocation ID:
- p. 1339-1357
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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