Canonical signal recognition particle components can be bypassed for posttranslational protein targeting in chloroplasts.
The chloroplast signal recognition particle (cpSRP) and its receptor (cpFtsY) target proteins both cotranslationally and posttranslationally to the thylakoids. This dual function enables cpSRP to utilize its posttranslational activities for targeting a family of nucleus-encoded light-harvesting chlorophyll binding proteins (LHCPs), the most abundant membrane proteins in plants. Previous in vitro experiments indicated an absolute requirement for all cpSRP pathway soluble components. In agreement, a cpFtsY mutant in Arabidopsis thaliana exhibits a severe chlorotic phenotype resulting from a massive loss of LHCPs. Surprisingly, a double mutant, cpftsy cpsrp54, recovers to a great extent from the chlorotic cpftsy phenotype. This establishes that in plants, a new alternative pathway exists that can bypass cpSRP posttranslational targeting activities. Using a mutant form of cpSRP43 that is unable to assemble with cpSRP54, we complemented the cpSRP43-deficient mutant and found that this subunit is required for the alternative pathway. Along with the ability of cpSRP43 alone to bind the ALBINO3 translocase required for LHCP integration, our results indicate that cpSRP43 has developed features to function independently of cpSRP54/cpFtsY in targeting LHCPs to the thylakoid membranes.
Tzvetkova-Chevolleau
Tzvetelina
T
Direction des Sciences du Vivant, Institut de Biologie Environementale et de Biotechnologie, Service de Biologie Végétale et de Microbiologie Environementale, Commissariat à l'Energie Atomique Cadarache, F-13108 Saint-Paul-lez-Durance Cedex, France.
Hutin
Claire
C
Noël
Laurent D
LD
Goforth
Robyn
R
Carde
Jean-Pierre
JP
Caffarri
Stephano
S
Sinning
Irmgard
I
Groves
Matthew
M
Teulon
Jean-Marie
JM
Hoffman
Neil E
NE
Henry
Ralph
R
Havaux
Michel
M
Nussaume
Laurent
L
D017360:Arabidopsis / Q000378:metabolism* / Q000648:ultrastructure; D029681:Arabidopsis Proteins / Q000378:metabolism*; D002734:Chlorophyll / Q000378:metabolism; D060365:Chloroplast Proteins; D002736:Chloroplasts / Q000378:metabolism* / Q000648:ultrastructure; D019281:Dimerization; D005453:Fluorescence; D005816:Genetic Complementation Test; D045342:Light-Harvesting Protein Complexes / Q000378:metabolism; D008565:Membrane Proteins / Q000378:metabolism; D008954:Models, Biological; D009154:Mutation / Q000235:genetics; D010641:Phenotype; D011485:Protein Binding; D021381:Protein Transport; D018271:Signal Recognition Particle / Q000378:metabolism*; D020524:Thylakoids / Q000378:metabolism
C106404:ALBINO 3 protein, Arabidopsis; D029681:Arabidopsis Proteins; D060365:Chloroplast Proteins; C083707:FFC protein, Arabidopsis; D045342:Light-Harvesting Protein Complexes; D008565:Membrane Proteins; D018271:Signal Recognition Particle; C513946:cpFtsY protein, Arabidopsis; D002734:Chlorophyll