Cloning Two Genes for Nicotianamine Aminotransferase, a Critical Enzyme in Iron Acquisition (Strategy II) in Graminaceous Plants

• Published in: Plant physiology (Bethesda) Vol. 121; no. 3; pp. 947 - 956
• Main Authors: Takahashi, Michiko, Hirotaka Yamaguchi, Nakanishi, Hiromi, Shioiri, Takayuki, Naoko-Kishi Nishizawa, Mori, Satoshi
• Format: Journal Article
• Language: English
• Published: Rockville, MD American Society of Plant Physiologists 01.11.1999
• Subjects: Agronomy. Soil science and plant productions; Amino Acid Sequence; Amino acids; Barley; Base Sequence; Biological and medical sciences; Classical and quantitative genetics. Population genetics. Molecular genetics; Cloning, Molecular; Complementary DNA; Environmental and Stress Physiology; Enzymes; Fundamental and applied biological sciences. Psychology; Gels; Generalities. Genetics. Plant material; Genes. Genome; Genetics and breeding of economic plants; Genomic Library; Hordeum - enzymology; Hordeum - genetics; Hordeum vulgare; Iron - metabolism; Isoenzymes - chemistry; Isoenzymes - genetics; Isoenzymes - metabolism; Kinetics; Molecular and cellular biology; Molecular genetics; Molecular Sequence Data; mugineic acid; naat-A gene; naat-B gene; Nicotianamine; Nicotianamine aminotransferase; Nucleic acid amplification techniques; phytosiderophore; Plant Proteins; Plant roots; Plants; Proteins; Recombinant Proteins - isolation & purification; Recombinant Proteins - metabolism; Sequence Alignment; Sequence Homology, Amino Acid; Transaminases - chemistry; Transaminases - genetics; Transaminases - metabolism; Yeasts; Monocotyledones; Hordeum vulgare; Nutrition; Nucleotide sequence; Enzyme; Transferases; Deficiency; Iron chlorosis; Iron; Cereal crop; α-Aminoacid; Fixation; Gene; Gramineae; Transaminases; Angiospermae; Chelating agent; Spermatophyta; Molecular cloning; Aminoacid sequence
• ISSN: 0032-0889; 1532-2548
• DOI: 10.1104/pp.121.3.947

Nicotianamine aminotransferase (NAAT), the key enzyme involved in the biosynthesis of mugineic acid family phytosiderophores (MAs), catalyzes the amino transfer of nicotianamine (NA). MAs are found only in graminaceous plants, although NA has been detected in every plant so far investigated. Therefore, this amino transfer reaction is the first step in the unique biosynthesis of MAs that has evolved in graminaceous plants. NAAT activity is dramatically induced by Fe deficiency and suppressed by Fe resupply. Based on the protein sequence of NAAT purified from Fe-deficient barley (Hordeum vulgare) roots, two distinct cDNA clones encoding NAAT, naat-A and naat-B, were identified. Their deduced amino acid sequences were homologous to several aminotransferases, and shared consensus sequences for the pyridoxal phosphate-binding site lysine residue and its surrounding residues. The expression of both naat-A and naat-B is increased in Fe-deficient barley roots, while naat-B has a low level of constitutive expression in Fe-sufficient barley roots. No detectable mRNA from either naat-A or naat-B was present in the leaves of either Fe-deficient or Fe-sufficient barley. One genomic clone with a tandem array of naat-B and naat-A in this order was identified. naat-B and naat-A each have six introns at the same locations. The isolation of NAAT genes will pave the way to understanding the mechanism of the response to Fe in graminaceous plants, and may lead to the development of cultivars tolerant to Fe deficiency that can grow in calcareous soils.