Unraveling the role of transient starch in the response of Arabidopsis to elevated CO2 under long-day conditions

Previous studies on Arabidopsis under long-term exposure to elevated CO2 have been conducted using starch synthesis and breakdown mutants cultured under short day conditions. These studies showed that starch synthesis can ameliorate the photosynthetic reduction caused by soluble sugar-mediated feedback regulation. In this work we characterized the effect of long-term exposure to elevated CO2 (800 ppm) on growth, photosynthesis and content of primary photosynthates in long-day grown wild type plants as well as the near starch-less (aps1) and the starch-excess (gwd) mutants. Notably, elevated CO2 promoted growth of both wild type and aps1 plants but had no effect on gwd plants. Growth promotion by elevated CO2 was accompanied by an increased net photosynthesis in WT and aps1 plants. However, the plants with the highest starch content (wild type at elevated CO2, gwd at ambient CO2, and gwd at elevated CO2) were the ones that suffered decreased in in vivo maximum carboxylation rate of Rubisco, and therefore, photosynthetic down-regulation. Further, the photosynthetic rates of wild type at elevated CO2 and gwd at elevated CO2 were acclimated to elevated CO2. Notably, elevated CO2 promoted the accumulation of stress-responsive and senescence-associated amino acid markers in gwd plants. The results presented in this work provide evidence that under long-day conditions, temporary storage of overflow photosynthate as starch negatively affect Rubisco performance. These data are consistent with earlier hypothesis that photosynthetic acclimation can be caused by accelerated senescence and hindrance of CO2 diffusion to the stroma due to accumulation of large starch granules

GlgS, previously described as a glycogen synthesis control protein, negatively regulates motility and biofilm formation in Escherichia coli

Escherichia coli glycogen metabolism involves regulation of the glgBXCAP operon expression and allosteric control of GlgC-mediated catalysis of ATP and glucose-1-phosphate (G1P) to ADP-glucose linked to glycogen biosynthesis. E. coli glycogen metabolism is also affected by glgS. Though the precise function of the protein it encodes is unknown, its deficiency causes both reduced glycogen content and enhanced levels of the GlgC negative allosteric regulator AMP. Transcriptomic analyses carried out in this work revealed that, compared with their isogenic BW25113 wild type strain, glgS null (DglgS) mutants have increased expression of operons involved in the synthesis of type 1 fimbriae adhesins, flagella, and nucleotides. In concordance, ÄglgS cells were hyperflagellated and hyperfimbriated, and displayed elevated swarming motility; these phenotypes were all reverted by ectopic glgS expression. Also, DglgS cells accumulated high colanic acid content, and displayed increased ability to form biofilms on polysterene surfaces. F-driven conjugation based large-scale interaction studies of glgS with all the nonessential genes of E. coli showed that deletion of purine biosynthesis genes complement the glycogen-deficient, high motility and high biofilm content phenotypes of DglgS cells. Overall, these data indicate that glycogen deficiency in ÄglgS cells can be ascribed to high flagellar propulsion, and high exopolysaccharide and purine nucleotides biosynthetic activites competing with GlgC for the same ATP and G1P pools. Supporting this proposal, glycogen-less DglgC cells displayed an elevated swarming motility, and accumulated high levels of colanic acid and biofilm. Furthermore, glgC over-expression reverted the glycogen-deficient, high swarming motility, high colanic acid and high biofilm content phenotypes of DglgS cells. Because GlgS emerges now as a major determinant of E. coli surface composition, and because its effect on glycogen metabolism appears to be only indirect, we propose to rename it as ScoR for Surface Composition Regulator.Fil: Rahimpour, Mehdi. Consejo Superior de Investigaciones Cientificas. Instituto de Agrobiotecnología; EspañaFil: Montero, Manuel. Consejo Superior de Investigaciones Cientificas. Instituto de Agrobiotecnología; EspañaFil: Almagro, Goizeder. Consejo Superior de Investigaciones Cientificas. Instituto de Agrobiotecnología; EspañaFil: Viale, Alejandro Miguel. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Rosario. Instituto de Biología Molecular y Celular de Rosario; Argentina. Consejo Superior de Investigaciones Cientificas. Instituto de Agrobiotecnología; EspañaFil: Sevilla, Angel. Universidad de Murcia. Facultad de Química. Departamento de Bioquímica y Biología Molecular e Inmunología; EspañaFil: Cánovas, Manuel. Universidad de Murcia. Facultad de Química. Departamento de Bioquímica y Biología Molecular e Inmunología; EspañaFil: Muñoz, Francisco J.. Consejo Superior de Investigaciones Cientificas. Instituto de Agrobiotecnología; EspañaFil: Baroja Fernandez, Edurne. Consejo Superior de Investigaciones Cientificas. Instituto de Agrobiotecnología; EspañaFil: Bahaji, Abdellatif. Consejo Superior de Investigaciones Cientificas. Instituto de Agrobiotecnología; EspañaFil: Eydallin, Gustavo. Consejo Superior de Investigaciones Cientificas. Instituto de Agrobiotecnología; EspañaFil: Dose, Hitomi. Nara Institute of Science and Technology. Graduate School of Biological Sciences; JapónFil: Takeuchi, Rikiya. Nara Institute of Science and Technology. Graduate School of Biological Sciences; JapónFil: Mori, Hirotada. Nara Institute of Science and Technology. Graduate School of Biological Sciences; JapónFil: Pozueta Romero, Javier. Consejo Superior de Investigaciones Cientificas. Instituto de Agrobiotecnología; Españ