Cloning and characterization of deoxymugineic acid synthase genes from graminaceous plants.
Graminaceous plants have evolved a unique mechanism to acquire iron through the secretion of a family of small molecules, called mugineic acid family phytosiderophores (MAs). All MAs are synthesized from l-Met, sharing the same pathway from l-Met to 2'-deoxymugineic acid (DMA). DMA is synthesized through the reduction of a 3''-keto intermediate by deoxymugineic acid synthase (DMAS). We have isolated DMAS genes from rice (OsDMAS1), barley (HvDMAS1), wheat (TaD-MAS1), and maize (ZmDMAS1). Their nucleotide sequences indicate that OsDMAS1 encodes a predicted polypeptide of 318 amino acids, whereas the other three orthologs all encode predicted polypeptides of 314 amino acids and are highly homologous (82-97.5%) to each other. The DMAS proteins belong to the aldo-keto reductase superfamily 4 (AKR4) but do not fall within the existing subfamilies of AKR4 and appear to constitute a new subfamily within the AKR4 group. All of the proteins showed DMA synthesis activity in vitro. Their enzymatic activities were highest at pH 8-9, consistent with the hypothesis that DMA is synthesized in subcellular vesicles. Northern blot analysis revealed that the expression of each of the above DMAS genes is up-regulated under iron-deficient conditions in root tissue, and that of the genes OsDMAS1 and TaDMAS1 is up-regulated in shoot tissue. OsDMAS1 promoter-GUS analysis in iron-sufficient roots showed that its expression is restricted to cells participating in long distance transport and that it is highly up-regulated in the entire root under iron-deficient conditions. In shoot tissue, OsDMAS1 promoter drove expression in vascular bundles specifically under iron-deficient conditions.
Bashir
Khurram
K
Graduate School of Agricultural and Life Sciences, The University of Tokyo, 1-1-1 Yayoi, Bunkyo-ku, Tokyo 113-8657.
Inoue
Haruhiko
H
Nagasaka
Seiji
S
Takahashi
Michiko
M
Nakanishi
Hiromi
H
Mori
Satoshi
S
Nishizawa
Naoko K
NK
D000595:Amino Acid Sequence; D001383:Azetidinecarboxylic Acid / Q000031:analogs & derivatives / Q000378:metabolism; D003001:Cloning, Molecular; D017343:Genes, Plant; D001467:Hordeum / Q000201:enzymology* / Q000235:genetics; D006863:Hydrogen-Ion Concentration; D007150:Immunohistochemistry; D007501:Iron / Q000378:metabolism; D000090463:Iron Deficiencies; D006899:Mixed Function Oxygenases / Q000737:chemistry / Q000235:genetics* / Q000302:isolation & purification / Q000378:metabolism; D008969:Molecular Sequence Data; D012275:Oryza / Q000201:enzymology* / Q000235:genetics; D010802:Phylogeny; D018517:Plant Roots / Q000235:genetics / Q000378:metabolism; D030821:Plants, Genetically Modified / Q000201:enzymology / Q000235:genetics; D010957:Plasmids; D011401:Promoter Regions, Genetic; D011994:Recombinant Proteins / Q000737:chemistry / Q000378:metabolism; D017386:Sequence Homology, Amino Acid; D017262:Siderophores / Q000096:biosynthesis; D014908:Triticum / Q000201:enzymology* / Q000235:genetics; D003313:Zea mays / Q000201:enzymology* / Q000235:genetics
D011994:Recombinant Proteins; D017262:Siderophores; D001383:Azetidinecarboxylic Acid; D007501:Iron; D006899:Mixed Function Oxygenases; C052863:mugineic acid