title: Genotypic variation in sulfur assimilation and metabolism of onion (Allium cepa L.) III. Characterization of sulfite reductase.
abstract: Genomic and cDNA sequences corresponding to a ferredoxin-sulfite reductase (SiR) have been cloned from bulb onion (Allium cepa L.) and the expression of the gene and activity of the enzyme characterized with respect to sulfur (S) supply. Cloning, mapping and expression studies revealed that onion has a single functional SiR gene and also expresses an unprocessed pseudogene (φ-SiR). Northern and qPCR analysis revealed differences in expression pattern between the SiR gene and the pseudogene. Western analysis using antibodies raised to a recombinant SiR revealed that the enzyme is present in chloroplasts and phylogenetic analysis has shown that the onion protein groups with lower eudicots. In hydroponically-grown plants, levels of SiR transcripts were significantly higher in the roots of S-sufficient when compared with S-deficient plants of the pungent cultivar 'W202A' but not the less pungent cultivar 'Texas Grano'. In these same treatments, a higher level of enzyme activity was observed in the S-sufficient treatment in leaves of both cultivars before and after bulbing. In a factorial field trial with and without sulfur fertilization, a statistically significant increase in SiR activity was observed in the leaves of the pungent cultivar 'Kojak' in response to added S but not in the less pungent cultivar 'Encore'.
authors.affiliation: Institute of Molecular BioSciences, Massey University, Private Bag 11222, Palmerston North, New Zealand. M.T.McManus@massey.ac.nz
authors.forename: Michael T
authors.initials: MT
authors.lastname: McManus
authors.forename: Srishti
authors.initials: S
authors.lastname: Joshi
authors.forename: Bruce
authors.initials: B
authors.lastname: Searle
authors.forename: Meeghan
authors.initials: M
authors.lastname: Pither-Joyce
authors.forename: Martin
authors.initials: M
authors.lastname: Shaw
authors.forename: Susanna
authors.initials: S
authors.lastname: Leung
authors.forename: Nick
authors.initials: N
authors.lastname: Albert
authors.forename: Masayoshi
authors.initials: M
authors.lastname: Shigyo
authors.forename: Jernej
authors.initials: J
authors.lastname: Jakse
authors.forename: Michael J
authors.initials: MJ
authors.lastname: Havey
authors.forename: John
authors.initials: J
authors.lastname: McCallum
mesh_terms: D003001:Cloning, Molecular; D004789:Enzyme Activation; D015971:Gene Expression Regulation, Enzymologic; D018506:Gene Expression Regulation, Plant / Q000235:genetics; D014644:Genetic Variation / Q000235:genetics*; D005838:Genotype; D019697:Onions / Q000201:enzymology* / Q000378:metabolism*; D020133:Reverse Transcriptase Polymerase Chain Reaction; D050889:Sulfite Reductase (Ferredoxin) / Q000235:genetics* / Q000378:metabolism; D013455:Sulfur / Q000378:metabolism*
chemical_list: D013455:Sulfur; D050889:Sulfite Reductase (Ferredoxin)