A SecY homologue is required for the elaboration of the chloroplast thylakoid membrane and for normal chloroplast gene expression.
Results of in vitro and genetic studies have provided evidence for four pathways by which proteins are targeted to the chloroplast thylakoid membrane. Although these pathways are initially engaged by distinct substrates and involve some distinct components, an unresolved issue has been whether multiple pathways converge on a common translocation pore in the membrane. A homologue of eubacterial SecY called cpSecY is localized to the thylakoid membrane. Since SecY is a component of a protein-translocating pore in bacteria, cpSecY likely plays an analogous role. To explore the role of cpSecY, we obtained maize mutants with transposon insertions in the corresponding gene. Null cpSecY mutants exhibit a severe loss of thylakoid membrane, differing in this regard from mutants lacking cpSecA. Therefore, cpSecY function is not limited to a translocation step downstream of cpSecA. The phenotype of cpSecY mutants is also much more pleiotropic than that of double mutants in which both the cpSecA- and DeltapH-dependent thylakoid-targeting pathways are disrupted. Therefore, cpSecY function is likely to extend beyond any role it might play in these targeting pathways. CpSecY mutants also exhibit a defect in chloroplast translation, revealing a link between chloroplast membrane biogenesis and chloroplast gene expression.
Roy
L M
LM
Institute of Molecular Biology, University of Oregon, Eugene, Oregon 97403, USA.
Barkan
A
A
D000595:Amino Acid Sequence; D029681:Arabidopsis Proteins; D001483:Base Sequence; D060365:Chloroplast Proteins; D002736:Chloroplasts / Q000235:genetics* / Q000648:ultrastructure; D003001:Cloning, Molecular; D003624:Darkness; D018628:Gene Dosage; D018506:Gene Expression Regulation, Plant / Q000502:physiology*; D017343:Genes, Plant / Q000235:genetics; D007425:Intracellular Membranes / Q000502:physiology* / Q000648:ultrastructure; D008565:Membrane Proteins / Q000032:analysis / Q000235:genetics / Q000502:physiology*; D008969:Molecular Sequence Data; D009154:Mutation; D010641:Phenotype; D010940:Plant Proteins / Q000032:analysis / Q000235:genetics / Q000502:physiology*; D011132:Polyribosomes / Q000737:chemistry; D012333:RNA, Messenger / Q000032:analysis; D018749:RNA, Plant / Q000032:analysis; D012336:RNA, Ribosomal, 16S / Q000032:analysis; D000069816:SEC Translocation Channels; D017422:Sequence Analysis, DNA; D017386:Sequence Homology, Amino Acid; D003313:Zea mays / Q000235:genetics*
D029681:Arabidopsis Proteins; D060365:Chloroplast Proteins; D008565:Membrane Proteins; D010940:Plant Proteins; D012333:RNA, Messenger; D018749:RNA, Plant; D012336:RNA, Ribosomal, 16S; C000613370:SCY1 protein, Arabidopsis; D000069816:SEC Translocation Channels