title: The bacterial stringent response, conserved in chloroplasts, controls plant fertilization.
abstract: The chloroplast, an essential organelle for plants, performs a wide variety of metabolic processes for host cells, which include photosynthesis as well as amino acid and fatty acid biosynthesis. The organelle conserves many bacterial systems in its functions, implicating its origin from symbiosis of a photosynthetic bacterium. In bacterial cells, the stringent response acts as a global regulatory system for gene expression mediated by a small nucleotide, guanosine 5'-diphosphate 3'-diphosphate (ppGpp), that is necessary for cell adaptation to diverse environmental stimuli such as amino acid starvation. Recent studies indicated that proteins similar to the bacterial ppGpp synthase/hydrolyase are conserved in plants, although their precise roles are not known. Here we show that the stringent response in chloroplasts is crucial for normal plant fertilization. Specifically, one of the Arabidopsis ppGpp synthase homologs, CRSH (Ca(2+)-activated RelA/SpoT homolog), exhibits calcium-dependent ppGpp synthesis activity in vitro, and is localized in chloroplasts in vivo. A knockdown mutation of CRSH in Arabidopsis results in a significant reduction in silique size and seed production, indicating that plant reproduction is under the control of chloroplast function through a ppGpp-mediated stringent response.
authors.affiliation: Graduate School of Bioscience and Biotechnology, Tokyo Institute of Technology, Yokohama, 226-8501 Japan. shmasuda@bio.titech.ac.jp
authors.forename: Shinji
authors.initials: S
authors.lastname: Masuda
authors.forename: Kazuki
authors.initials: K
authors.lastname: Mizusawa
authors.forename: Takakuni
authors.initials: T
authors.lastname: Narisawa
authors.forename: Yuzuru
authors.initials: Y
authors.lastname: Tozawa
authors.forename: Hiroyuki
authors.initials: H
authors.lastname: Ohta
authors.forename: Ken-Ichiro
authors.initials: K
authors.lastname: Takamiya
mesh_terms: D000595:Amino Acid Sequence; D017360:Arabidopsis / Q000235:genetics / Q000502:physiology*; D029681:Arabidopsis Proteins / Q000235:genetics / Q000378:metabolism*; D002736:Chloroplasts / Q000235:genetics / Q000378:metabolism*; D017124:Conserved Sequence; D005306:Fertilization / Q000235:genetics / Q000502:physiology*; D035264:Flowers / Q000235:genetics / Q000254:growth & development; D017353:Gene Deletion; D018506:Gene Expression Regulation, Plant; D008025:Ligases / Q000235:genetics / Q000378:metabolism*
chemical_list: D029681:Arabidopsis Proteins; C529134:CRSH protein, Arabidopsis; D008025:Ligases