Abstract
Chloroplasts possess a system for generating (p)ppGpp, which triggers the stringent response in eubacteria. Here we present the identification and characterization of genes for a novel type of (p)ppGpp synthetase (CRSH) in rice and Arabidopsis. The proteins encoded by these genes contain a putative chloroplast transit peptide at the N-terminus, a central RelA-SpoT like domain, and two EF-hand motifs at the C-terminus. The recombinant OsCRSH1 protein was imported into chloroplasts in vitro. Biochemical analysis showed that the OsCRSH proteins possess (p)ppGpp synthetase activity that is dependent both on Ca2+ and on the EF-hand motifs. CRSH proteins thus likely function as Ca2+-activated (p)ppGpp synthetases in plant chloroplasts, implicating both Ca2+ and (p)ppGpp signaling in regulation of the genetic system of these organelles.
Tozawa Y. et al. J. Biol. Chem. 282, 35536-35545, 2007.
