Interference with plastome gene expression and Clp protease activity in Arabidopsis triggers a chloroplast unfolded protein response to restore protein homeostasis
Llamas, Ernesto (Centre de Recerca en Agrigenòmica)
Pulido, Pablo (Centre de Recerca en Agrigenòmica)
Rodríguez Concepción, Manuel (Centre de Recerca en Agrigenòmica)

Date:	2017
Abstract:	Disruption of protein homeostasis in chloroplasts impairs the correct functioning of essential metabolic pathways, including the methylerythritol 4-phosphate (MEP) pathway for the production of plastidial isoprenoids involved in photosynthesis and growth. We previously found that misfolded and aggregated forms of the first enzyme of the MEP pathway are degraded by the Clp protease with the involvement of Hsp70 and Hsp100/ClpC1 chaperones in Arabidopsis thaliana. By contrast, the combined unfolding and disaggregating actions of Hsp70 and Hsp100/ClpB3 chaperones allow solubilization and hence reactivation of the enzyme. The repair pathway is promoted when the levels of ClpB3 proteins increase upon reduction of Clp protease activity in mutants or wild-type plants treated with the chloroplast protein synthesis inhibitor lincomycin (LIN). Here we show that LIN treatment rapidly increases the levels of aggregated proteins in the chloroplast, unleashing a specific retrograde signaling pathway that up-regulates expression of ClpB3 and other nuclear genes encoding plastidial chaperones. As a consequence, folding capacity is increased to restore protein homeostasis. This sort of chloroplast unfolded protein response (cpUPR) mechanism appears to be mediated by the heat shock transcription factor HsfA2. Expression of HsfA2 and cpUPR-related target genes is independent of GUN1, a central integrator of retrograde signaling pathways. However, double mutants defective in both GUN1 and plastome gene expression (or Clp protease activity) are seedling lethal, confirming that the GUN1 protein is essential for protein homeostasis in chloroplasts.
Grants:	Ministerio de Economía y Competitividad BIO2015-71703-REDT Ministerio de Economía y Competitividad SEV-2015-0533 Ministerio de Economía y Competitividad BIO2014-59092-P Agència de Gestió d'Ajuts Universitaris i de Recerca 2014/SGR-1434
Rights:	Aquest document està subjecte a una llicència d'ús Creative Commons. Es permet la reproducció total o parcial, la distribució, la comunicació pública de l'obra i la creació d'obres derivades, fins i tot amb finalitats comercials, sempre i quan es reconegui l'autoria de l'obra original.
Language:	Anglès
Document:	Article ; recerca ; Versió publicada
Subject:	Chloroplasts ; Proteases ; Arabidopsis thaliana ; Gene expression ; Seedlings ; Transcription factors ; Heat shock response ; Chlorophyll
Published in:	PLoS Genetics, Vol. 13, issue 9 (set. 2017) , e1007022, ISSN 1553-7404

DOI: 10.1371/journal.pgen.1007022
PMID: 28937985

27 p, 5.9 MB

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Research literature > UAB research groups literature > Research Centres and Groups (research output) > Experimental sciences > CRAG (Centre for Research in Agricultural Genomics)
Articles > Research articles
Articles > Published articles