Phosphate Assimilation in Rhizobium(Sinorhizobium) meliloti: Identification of apit-Like Gene Academic Article uri icon

  •  
  • Overview
  •  
  • Research
  •  
  • Identity
  •  
  • Additional Document Info
  •  
  • View All
  •  

abstract

  • ABSTRACTRhizobium melilotimutants defective in thephoCDET-encoded phosphate transport system form root nodules on alfalfa plants that fail to fix nitrogen (Fix). We have previously reported that two classes of second-site mutations can suppress the Fixphenotype ofphoCDETmutants to Fix+. Here we show that one of these suppressor loci (sfx1) contains two genes,orfAandpit, which appear to form an operon transcribed in the orderorfA-pit. The Pit protein is homologous to various phosphate transporters, and we present evidence that three suppressor mutations arose from a single thymidine deletion in a hepta-thymidine sequence centered 54 nucleotides upstream of theorfAtranscription start site. This mutation increased the level oforfA-pittranscription. These data, together with previous biochemical evidence, show that theorfA-pitgenes encode a Pitransport system that is expressed in wild-type cells grown with excess Pibut repressed in cells under conditions of Pilimitation. InphoCDETmutant cells,orfA-pitexpression is repressed, but this repression is alleviated by the second-site suppressor mutations. Suppression increasesorfA-pitexpression compensating for the deficiencies in phosphate assimilation and symbiosis of thephoCDETmutants.

publication date

  • August 15, 1998