Three nicotianamine synthase genes isolated from maize are differentially regulated by iron nutritional status.
Nicotianamine synthase (NAS) is an enzyme that is critical for the biosynthesis of the mugineic acid family of phytosiderophores in graminaceous plants, and for the homeostasis of metal ions in nongraminaceous plants. We isolated one genomic NAS clone, ZmNAS3, and two cDNA NAS clones, ZmNAS1 and ZmNAS2, from maize (Zea mays cv Alice). In agreement with the increased secretion of phytosiderophores with Fe deficiency, ZmNAS1 and ZmNAS2 were positively expressed only in Fe-deficient roots. In contrast, ZmNAS3 was expressed under Fe-sufficient conditions, and was negatively regulated by Fe deficiency. This is the first report describing down-regulation of NAS gene expression in response to Fe deficiency in plants, shedding light on the role of nicotianamine in graminaceous plants, other than as a precursor in phytosiderophore production. ZmNAS1-green fluorescent protein (sGFP) and ZmNAS2-sGFP were localized at spots in the cytoplasm of onion (Allium cepa) epidermal cells, whereas ZmNAS3-sGFP was distributed throughout the cytoplasm of these cells. ZmNAS1 and ZmNAS3 showed NAS activity in vitro, whereas ZmNAS2 showed none. Due to its duplicated structure, ZmNAS2 was much larger (65.8 kD) than ZmNAS1, ZmNAS3, and previously characterized NAS proteins (30-38 kD) from other plant species. We reveal that maize has two types of NAS proteins based on their expression pattern and subcellular localization.
Mizuno
Daichi
D
Department of Applied Biological Chemistry, Graduate School of Agricultural and Life Science, University of Tokyo, 1-1-1 Yayoi, Bunkyo-ku, Tokyo 113-8657, Japan.
Higuchi
Kyoko
K
Sakamoto
Tatsuya
T
Nakanishi
Hiromi
H
Mori
Satoshi
S
Nishizawa
Naoko K
NK
D019883:Alkyl and Aryl Transferases / Q000235:genetics* / Q000378:metabolism*; D000595:Amino Acid Sequence; D015153:Blotting, Western; D003001:Cloning, Molecular; D018076:DNA, Complementary / Q000235:genetics; D020869:Gene Expression Profiling; D015971:Gene Expression Regulation, Enzymologic / Q000187:drug effects; D018506:Gene Expression Regulation, Plant / Q000187:drug effects*; D007501:Iron / Q000494:pharmacology*; D008969:Molecular Sequence Data; D016366:Open Reading Frames / Q000235:genetics; D010802:Phylogeny; D018517:Plant Roots / Q000201:enzymology; D017386:Sequence Homology, Amino Acid; D003313:Zea mays / Q000187:drug effects* / Q000201:enzymology* / Q000235:genetics
D018076:DNA, Complementary; D007501:Iron; D019883:Alkyl and Aryl Transferases; C118230:nicotianamine synthase