The sulfate transporter SST1 is crucial for symbiotic nitrogen fixation in Lotus japonicus root nodules.
Symbiotic nitrogen fixation (SNF) by intracellular rhizobia within legume root nodules requires the exchange of nutrients between host plant cells and their resident bacteria. Little is known at the molecular level about plant transporters that mediate such exchanges. Several mutants of the model legume Lotus japonicus have been identified that develop nodules with metabolic defects that cannot fix nitrogen efficiently and exhibit retarded growth under symbiotic conditions. Map-based cloning of defective genes in two such mutants, sst1-1 and sst1-2 (for symbiotic sulfate transporter), revealed two alleles of the same gene. The gene is expressed in a nodule-specific manner and encodes a protein homologous with eukaryotic sulfate transporters. Full-length cDNA of the gene complemented a yeast mutant defective in sulfate transport. Hence, the gene was named Sst1. The sst1-1 and sst1-2 mutants exhibited normal growth and development under nonsymbiotic growth conditions, a result consistent with the nodule-specific expression of Sst1. Data from a previous proteomic study indicate that SST1 is located on the symbiosome membrane in Lotus nodules. Together, these results suggest that SST1 transports sulfate from the plant cell cytoplasm to the intracellular rhizobia, where the nutrient is essential for protein and cofactor synthesis, including nitrogenase biosynthesis. This work shows the importance of plant sulfate transport in SNF and the specialization of a eukaryotic transporter gene for this purpose.
Krusell
Lene
L
Max Planck Institute of Molecular Plant Physiology, 14476 Golm, Germany.
Krause
Katja
K
Ott
Thomas
T
Desbrosses
Guilhem
G
Krämer
Ute
U
Sato
Shusei
S
Nakamura
Yasukazu
Y
Tabata
Satoshi
S
James
Euan K
EK
Sandal
Niels
N
Stougaard
Jens
J
Kawaguchi
Masayoshi
M
Miyamoto
Ai
A
Suganuma
Norio
N
Udvardi
Michael K
MK
D000595:Amino Acid Sequence; D027321:Anion Transport Proteins / Q000235:genetics / Q000378:metabolism*; D029681:Arabidopsis Proteins / Q000235:genetics / Q000378:metabolism; D001483:Base Sequence; D002462:Cell Membrane / Q000378:metabolism; D003593:Cytoplasm / Q000378:metabolism; D018076:DNA, Complementary / Q000032:analysis / Q000235:genetics; D018506:Gene Expression Regulation, Plant / Q000235:genetics; D000070116:Lotus / Q000378:metabolism*; D026901:Membrane Transport Proteins / Q000235:genetics / Q000378:metabolism*; D008969:Molecular Sequence Data; D009154:Mutation / Q000235:genetics; D009584:Nitrogen / Q000378:metabolism; D009586:Nitrogen Fixation / Q000502:physiology*; D010802:Phylogeny; D010940:Plant Proteins / Q000235:genetics / Q000378:metabolism*; D018517:Plant Roots / Q000378:metabolism*; D021381:Protein Transport / Q000502:physiology; D000076988:Sulfate Transporters; D013431:Sulfates / Q000378:metabolism*; D013559:Symbiosis / Q000502:physiology
C108684:AST68 protein, Arabidopsis; D027321:Anion Transport Proteins; D029681:Arabidopsis Proteins; D018076:DNA, Complementary; D026901:Membrane Transport Proteins; D010940:Plant Proteins; D000076988:Sulfate Transporters; D013431:Sulfates; D009584:Nitrogen