Reference "Cloning and characterization of deoxymugineic acid synthase genes from graminaceous plants"

Reference ID

12308

Title

Cloning and characterization of deoxymugineic acid synthase genes from graminaceous plants

Source

The Journal of biological chemistry, 2006, vol. 281, pp. 32395-32402

Authors (7)

Bashir-K	Inoue-H
Nagasaka-S	Takahashi-M
Nakanishi-H	Mori-S
Nishizawa-N-K

Abstract

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.