title: Genome-wide identification, classification and expression profiling of nicotianamine synthase (NAS) gene family in maize.
abstract: BACKGROUND
  Nicotianamine (NA), a ubiquitous molecule in plants, is an important metal ion chelator and the main precursor for phytosiderophores biosynthesis. Considerable progress has been achieved in cloning and characterizing the functions of nicotianamine synthase (NAS) in plants including barley, Arabidopsis and rice. Maize is not only an important cereal crop, but also a model plant for genetics and evolutionary study. The genome sequencing of maize was completed, and many gene families were identified. Although three NAS genes have been characterized in maize, there is still no systematic identification of maize NAS family by genomic mining.
  
  
  RESULTS
  In this study, nine NAS genes in maize were identified and their expression patterns in different organs including developing seeds were determined. According to the evolutionary relationship and tissue specific expression profiles of ZmNAS genes, they can be subgrouped into two classes. Moreover, the expression patterns of ZmNAS genes in response to fluctuating metal status were analysed. The class I ZmNAS genes were induced under Fe deficiency and were suppressed under Fe excessive conditions, while the expression pattern of class II genes were opposite to class I. The complementary expression patterns of class I and class II ZmNAS genes confirmed the classification of this family. Furthermore, the histochemical localization of ZmNAS1;1/1;2 and ZmNAS3 were determined using in situ hybridization. It was revealed that ZmNAS1;1/1;2, representing the class I genes, mainly expressed in cortex and stele of roots with sufficient Fe, and its expression can expanded in epidermis, as well as shoot apices under Fe deficient conditions. On the contrary, ZmNAS3, one of the class II genes, was accumulated in axillary meristems, leaf primordia and mesophyll cells. These results suggest that the two classes of ZmNAS genes may be regulated on transcriptional level when responds to various demands for iron uptake, translocation and homeostasis.
  
  
  CONCLUSIONS
  These results provide significant insights into the molecular bases of ZmNAS in balancing iron uptake, translocation and homeostasis in response to fluctuating environmental Fe status.
authors.affiliation: Department of Crop Genomics & Genetic Improvement, Biotechnology Research Institute, Chinese Academy of Agricultural Sciences, Beijing, China.
authors.forename: Xiaojin
authors.initials: X
authors.lastname: Zhou
authors.forename: Suzhen
authors.initials: S
authors.lastname: Li
authors.forename: Qianqian
authors.initials: Q
authors.lastname: Zhao
authors.forename: Xiaoqing
authors.initials: X
authors.lastname: Liu
authors.forename: Shaojun
authors.initials: S
authors.lastname: Zhang
authors.forename: Cheng
authors.initials: C
authors.lastname: Sun
authors.forename: Yunliu
authors.initials: Y
authors.lastname: Fan
authors.forename: Chunyi
authors.initials: C
authors.lastname: Zhang
authors.forename: Rumei
authors.initials: R
authors.lastname: Chen
mesh_terms: D019883:Alkyl and Aryl Transferases / Q000737:chemistry / Q000235:genetics* / Q000378:metabolism; D000595:Amino Acid Sequence; D003001:Cloning, Molecular; D020869:Gene Expression Profiling; D018745:Genome, Plant / Q000235:genetics; D023281:Genomics; D006706:Homeostasis; D042541:Intracellular Space / Q000378:metabolism; D007501:Iron / Q000378:metabolism; D008969:Molecular Sequence Data; D010802:Phylogeny; D021381:Protein Transport; D003313:Zea mays / Q000166:cytology / Q000201:enzymology* / Q000235:genetics*
chemical_list: D007501:Iron; D019883:Alkyl and Aryl Transferases; C118230:nicotianamine synthase