title: Maize mutants lacking chloroplast FtsY exhibit pleiotropic defects in the biogenesis of thylakoid membranes.
abstract: A chloroplast signal recognition particle (SRP) that is related to the SRP involved in secretion in bacteria and eukaryotic cells is used for the insertion of light-harvesting chlorophyll proteins (LHCPs) into the thylakoid membranes. A conserved component of the SRP mechanism is a membrane-bound SRP receptor, denoted FtsY in bacteria. Plant genomes encode FtsY homologs that are targeted to the chloroplast (cpFtsY). To investigate the in vivo roles of cpFtsY, we characterized maize cpFtsY and maize mutants having a Mu transposon insertion in the corresponding gene (chloroplast SRP receptor1, or csr1). Maize cpFtsY accumulates to much higher levels in leaf tissue than in roots and stems. Interestingly, it is present at similar levels in etiolated and green leaf tissue and was found to bind the prolamellar bodies of etioplasts. A null cpFtsY mutant, csr1-1, showed a substantial loss of leaf chlorophyll, whereas a "leaky" allele, csr1-3, conditioned a more moderate chlorophyll deficiency. Both alleles caused the loss of various LHCPs and the thylakoid-bound photosynthetic enzyme complexes and were seedling lethal. By contrast, levels of the membrane-bound components of the thylakoid protein transport machineries were not altered. The thylakoid membranes in csr1-1 chloroplasts were unstacked and reduced in abundance, but the prolamellar bodies in mutant etioplasts appeared normal. These results demonstrate the essentiality of cpFtsY for the biogenesis not only of the LHCPs but also for the assembly of the other membrane-bound components of the photosynthetic apparatus.
authors.affiliation: Institute for Protein Research, Osaka University, Suita, Osaka 565-0871, Japan.
authors.forename: Yukari
authors.initials: Y
authors.lastname: Asakura
authors.forename: Toshiya
authors.initials: T
authors.lastname: Hirohashi
authors.forename: Shingo
authors.initials: S
authors.lastname: Kikuchi
authors.forename: Susan
authors.initials: S
authors.lastname: Belcher
authors.forename: Erin
authors.initials: E
authors.lastname: Osborne
authors.forename: Satoshi
authors.initials: S
authors.lastname: Yano
authors.forename: Ichiro
authors.initials: I
authors.lastname: Terashima
authors.forename: Alice
authors.initials: A
authors.lastname: Barkan
authors.forename: Masato
authors.initials: M
authors.lastname: Nakai
mesh_terms: D000595:Amino Acid Sequence; D001483:Base Sequence; D002736:Chloroplasts / Q000378:metabolism; D004251:DNA Transposable Elements / Q000235:genetics; D045342:Light-Harvesting Protein Complexes / Q000235:genetics / Q000378:metabolism*; D008969:Molecular Sequence Data; D009154:Mutation; D045332:Photosystem II Protein Complex / Q000235:genetics / Q000378:metabolism; D018515:Plant Leaves / Q000235:genetics / Q000378:metabolism; D010940:Plant Proteins / Q000235:genetics / Q000378:metabolism; D018160:Receptors, Cytoplasmic and Nuclear / Q000235:genetics / Q000378:metabolism*; D018000:Receptors, Peptide / Q000235:genetics / Q000378:metabolism*; D017386:Sequence Homology, Amino Acid; D018271:Signal Recognition Particle / Q000235:genetics / Q000378:metabolism; D020524:Thylakoids / Q000378:metabolism*; D003313:Zea mays / Q000235:genetics / Q000378:metabolism*
chemical_list: D004251:DNA Transposable Elements; D045342:Light-Harvesting Protein Complexes; D045332:Photosystem II Protein Complex; D010940:Plant Proteins; D018160:Receptors, Cytoplasmic and Nuclear; D018000:Receptors, Peptide; D018271:Signal Recognition Particle; C036318:signal peptide receptor