Cloning of two SOS1 transporters from the seagrass Cymodocea nodosa. SOS1 transporters from Cymodocea and Arabidopsis mediate potassium uptake in bacteria.
Two cDNAs isolated from Cymodocea nodosa, CnSOS1A, and CnSOSIB encode proteins with high-sequence similarities to SOS1 plant transporters. CnSOS1A expressed in a yeast Na+-efflux mutant under the control of a constitutive expression promoter mimicked AtSOS1 from Arabidopsis; the wild type cDNA did not improve the growth of the recipient strain in the presence of Na+, but a cDNA mutant that expresses a truncated protein suppressed the defect of the yeast mutant. In similar experiments, CnSOS1B was not effective. Conditional expression, under the control of an arabinose responsive promoter, of the CnSOSIA and CnSOS1B cDNAs in an Escherichia coli mutant defective in Na+ efflux was toxic, and functional analyses were inconclusive. The same constructs transformed into an E. coli K+-uptake mutant revealed that CnSOS1A was also toxic, but that it slightly suppressed defective growth at low K+. Truncation in the C-terminal hydrophilic tail of CnSOS1A relieved the toxicity and proved that CnSOS1A was an excellent low-affinity K+ and Rb+ transporter. CnSOS1B mediated a transient, extremely rapid K+ or Rb+ influx. Similar tests with AtSOS1 revealed that it was not toxic and that the whole protein exhibited excellent K+ and Rb+ uptake characteristics in bacteria.
Garciadeblás
Blanca
B
Departamento de Biotecnología, Escuela Técnica Superior de Ingenieros Agrónomos, Universidad Politécnica de Madrid, 28040 Madrid, Spain.
Haro
Rosario
R
Benito
Begoña
B
D000595:Amino Acid Sequence; D017360:Arabidopsis / Q000145:classification / Q000235:genetics*; D029681:Arabidopsis Proteins / Q000235:genetics / Q000378:metabolism; D001692:Biological Transport; D003001:Cloning, Molecular; D017124:Conserved Sequence; D018076:DNA, Complementary; D004926:Escherichia coli / Q000235:genetics / Q000378:metabolism; D008969:Molecular Sequence Data; D010802:Phylogeny; D006109:Poaceae / Q000235:genetics*; D011188:Potassium / Q000378:metabolism*; D011994:Recombinant Proteins / Q000378:metabolism; D012413:Rubidium / Q000378:metabolism; D020837:SOS1 Protein / Q000235:genetics* / Q000378:metabolism; D016415:Sequence Alignment; D017386:Sequence Homology, Amino Acid; D012964:Sodium / Q000378:metabolism; D017923:Sodium-Hydrogen Exchangers / Q000235:genetics* / Q000378:metabolism
D029681:Arabidopsis Proteins; D018076:DNA, Complementary; D011994:Recombinant Proteins; D020837:SOS1 Protein; C477653:SOS1 protein, Arabidopsis; D017923:Sodium-Hydrogen Exchangers; D012964:Sodium; D012413:Rubidium; D011188:Potassium