title: Characterization of the multigene family TaHKT 2;1 in bread wheat and the role of gene members in plant Na(+) and K(+) status.
abstract: BACKGROUND
  A member of the TaHKT2;1 multigene family was previously identified as a Na(+) transporter with a possible role in root Na(+) uptake. In the present study, the existing full-length cDNA of this member was used as a basis to query the International Wheat Genome Survey Sequence to identify all members of the TaHKT2;1 family. Individual TaHKT2;1 genes were subsequently studied for gene and predicted protein structures, promoter variability, tissue expression and their role in Na(+) and K(+) status of wheat.
  
  
  RESULTS
  Six TaHKT2;1 genes were characterized which included four functional genes (TaHKT2;1 7AL-1, TaHKT2;1 7BL-1, TaHKT2;1 7BL-2 and TaHKT2;1 7DL-1) and two pseudogenes (TaHKT2;1 7AL-2 and TaHKT2;1 7AL-3), on chromosomes 7A, 7B and 7D of hexaploid wheat. Variability in protein domains for cation specificity and in cis-regulatory elements for salt response in gene promoters, were identified amongst the functional TaHKT2;1 members. The functional genes were expressed under low and high NaCl conditions in roots and leaf sheaths, but were down regulated in leaf blades. Alternative splicing events were evident in TaHKT2;1 7AL-1. Aneuploid lines null for each functional gene were grown in high NaCl nutrient solution culture to identify potential role of each TaHKT2;1 member. Aneuploid lines null for TaHKT2;1 7AL-1, TaHKT2;1 7BL-1 and TaHKT2;1 7BL-2 showed no difference in Na(+) concentration between Chinese Spring except for higher Na(+) in sheaths. The same aneuploid lines had lower K(+) in roots, sheath and youngest fully expanded leaf but only under high (200 mM) NaCl in the external solution. There was no difference in Na(+) or K(+) concentration for any treatment between aneuploid line null for the TaHKT2;1 7DL-1 gene and Chinese Spring.
  
  
  CONCLUSIONS
  TaHKT2;1 is a complex family consisting of pseudogenes and functional members. TaHKT2;1 genes do not have an apparent role in controlling root Na(+) uptake in bread wheat seedlings under experimental conditions in this study, contrary to existing hypotheses. However, TaHKT2;1 genes or, indeed other genes in the same chromosome region on 7AL, are candidates that may control Na(+) transport from root to sheath and regulate K(+) levels in different plant tissues.
authors.forename: H A Chandima K
authors.initials: HA
authors.lastname: Ariyarathna
authors.forename: Tanveer
authors.initials: T
authors.lastname: Ul-Haq
authors.forename: Timothy D
authors.initials: TD
authors.lastname: Colmer
authors.affiliation: State Agricultural Biotechnology Centre, Murdoch University, Murdoch 6150, Western Australia. michael.francki@agric.wa.gov.au.
authors.forename: Michael G
authors.initials: MG
authors.lastname: Francki
mesh_terms: D000595:Amino Acid Sequence; D000782:Aneuploidy; D001483:Base Sequence; D001939:Bread; D002681:China; D002874:Chromosome Mapping; D005091:Exons / Q000235:genetics; D018506:Gene Expression Regulation, Plant; D017343:Genes, Plant; D057927:Hydrophobic and Hydrophilic Interactions; D054643:INDEL Mutation / Q000235:genetics; D007438:Introns / Q000235:genetics; D007477:Ions; D008969:Molecular Sequence Data; D005810:Multigene Family; D010940:Plant Proteins / Q000737:chemistry / Q000235:genetics* / Q000378:metabolism; D020641:Polymorphism, Single Nucleotide / Q000235:genetics; D011188:Potassium / Q000378:metabolism*; D011401:Promoter Regions, Genetic / Q000235:genetics; D011544:Pseudogenes; D017422:Sequence Analysis, DNA; D017384:Sequence Deletion / Q000235:genetics; D012964:Sodium / Q000378:metabolism*; D013045:Species Specificity; D014158:Transcription, Genetic; D014908:Triticum / Q000235:genetics*
chemical_list: D007477:Ions; D010940:Plant Proteins; D012964:Sodium; D011188:Potassium