title: Heterogeneity of sucrose synthase genes in bean (Phaseolus vulgaris L.): evidence for a nodule-enhanced sucrose synthase gene.
abstract: Sucrose synthase (SS), the key sucrose hydrolytic enzyme (EC 2.4.1.13), plays an important role in N(2)-fixing nodule metabolism. It has also been proposed that N(2) fixation in soybean nodules could be mediated by the potential to metabolize sucrose. The isolation and characterization of a nodule-enhanced SS full-length cDNA clone from the bean Phaseolus vulgaris is reported here. Southern blot analysis indicated that there are at least two SS genes in beans. Using a 3' specific probe from this SS cDNA clone, it was possible to identify a nodule-enhanced SS gene (PvSSn), which is expressed almost exclusively in nodules. A second gene (PvSS), which is expressed in all tissues tested, was detected using a coding region probe. Nodule-enhanced PvSSn transcript levels, but not the enzyme activity or protein amount, is reduced during nodule development. These data indicated that this reduction could be due to a limitation on the carbon availability in the nodule. PvSSn expression is reduced in the asparagine-treated nodules. By contrast, PvSSn transcript levels in nodules increased in the presence of glutamine, allantoin and allopurinol. This result suggests a relationship between ureide transport and SS regulation and could help in understanding why the ureide transport mechanism is activated during nitrogen fixation in bean.
authors.affiliation: Centro de Investigación sobre Fijación de Nitrógeno, Universidad Nacional Autónoma de México, Apartado Postal 565-A, Cuernavaca, Morelos, México.
authors.forename: Sonia
authors.initials: S
authors.lastname: Silvente
authors.forename: Alberto
authors.initials: A
authors.lastname: Camas
authors.forename: Miguel
authors.initials: M
authors.lastname: Lara
mesh_terms: D000481:Allantoin / Q000494:pharmacology; D000493:Allopurinol / Q000494:pharmacology; D000595:Amino Acid Sequence; D018076:DNA, Complementary / Q000737:chemistry / Q000235:genetics / Q000302:isolation & purification; D015971:Gene Expression Regulation, Enzymologic / Q000187:drug effects; D018506:Gene Expression Regulation, Plant / Q000187:drug effects; D005947:Glucose / Q000494:pharmacology; D005964:Glucosyltransferases / Q000235:genetics* / Q000378:metabolism; D005973:Glutamine / Q000494:pharmacology; D008969:Molecular Sequence Data; D009586:Nitrogen Fixation / Q000235:genetics / Q000502:physiology; D027805:Phaseolus / Q000201:enzymology* / Q000235:genetics / Q000382:microbiology; D010940:Plant Proteins / Q000235:genetics / Q000378:metabolism; D018517:Plant Roots / Q000201:enzymology / Q000235:genetics / Q000382:microbiology; D012231:Rhizobium / Q000254:growth & development; D017422:Sequence Analysis, DNA; D017386:Sequence Homology, Amino Acid; D013395:Sucrose / Q000494:pharmacology; D013559:Symbiosis; D015533:Transcriptional Activation / Q000187:drug effects
chemical_list: D018076:DNA, Complementary; D010940:Plant Proteins; D005973:Glutamine; D000481:Allantoin; D013395:Sucrose; D000493:Allopurinol; D005964:Glucosyltransferases; C022699:sucrose synthase; D005947:Glucose