Abstract
SummaryNicotianamine (NA) is a non‐protein amino acid involved in fundamental aspects of metal uptake, transport and homeostasis in all plants and constitutes the biosynthetic precursor of mugineic acid family phytosiderophores (MAs) in graminaceous plant species. Nicotianamine synthase (NAS) genes, which encode enzymes that synthesize NA from S‐adenosyl‐L‐methionine (SAM), are differentially regulated by iron (Fe) status in most plant species and plant genomes have been found to contain anywhere from 1 to 9 NAS genes. This study describes the identification of 21 NAS genes in the hexaploid bread wheat (Triticum aestivum L.) genome and their phylogenetic classification into two distinct clades. The TaNAS genes are highly expressed during germination, seedling growth and reproductive development. Fourteen of the clade I NAS genes were up‐regulated in root tissues under conditions of Fe deficiency. Protein sequence analyses revealed the presence of endocytosis motifs in all of the wheat NAS proteins as well as chloroplast, mitochondrial and secretory transit peptide signals in four proteins. These results greatly expand our knowledge of NAS gene families in graminaceous plant species as well as the genetics underlying Fe nutrition in bread wheat.
Highlights
Nicotianamine (NA) is a non-protein amino acid found in all higher plants (Noma and Noguchi, 1976; Noma et al, 1971)
Synthesis of NA occurs via trimerization of S-adenosylL-methionine (SAM) in a process catalysed by nicotianamine synthase (NAS) enzymes (Higuchi et al, 1994)
Nicotianamine is further converted to mugineic acid family phytosiderophores (MAs), such as 20-deoxymugineic acid (DMA), in graminaceous plant species that utilize Strategy II Fe uptake (Marschner and Romheld, 1994; Marschner et al, 1986)
Summary
Nicotianamine (NA) is a non-protein amino acid found in all higher plants (Noma and Noguchi, 1976; Noma et al, 1971). The chloronerva plants displayed retarded growth and signs of iron (Fe) deficiency despite containing high concentrations of Fe and other heavy metals in vegetative tissues, symptoms which were reversed upon exogenous application of NA. These findings, combined with threedimensional studies of NA structure, indicated that NA was crucial for in planta chelation, transport and homeostasis of Fe and other heavy metals (Budesinsky et al, 1980; Scholz et al, 1985). The release of MAs facilitates the growth of Strategy II plant species on calcareous soils where high pH impedes the Fe reductive approach utilized by Strategy I plants (Guerinot and Yi, 1994; Romheld et al, 1982; Scholz et al, 1992)
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