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Open Access Research article

Characterization of the multigene family TaHKT 2;1 in bread wheat and the role of gene members in plant Na+ and K+ status

HA Chandima K Ariyarathna12, Tanveer Ul-Haq123, Timothy D Colmer1 and Michael G Francki24*

Author Affiliations

1 School of Plant Biology and Institute of Agriculture, The University of Western Australia, Crawley 6009, Western Australia

2 State Agricultural Biotechnology Centre, Murdoch University, Murdoch 6150, Western Australia

3 College of Agriculture, D. G. Khan, University of Agriculture Faisalabad, Faisalabad 38040, Pakistan

4 Department of Agriculture and Food Western Australia, South Perth 6151, Western Australia

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BMC Plant Biology 2014, 14:159  doi:10.1186/1471-2229-14-159

Published: 11 June 2014

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.

Keywords:
IWGSS; Cis regulatory elements; Gene expression; Aneuploid lines; Tissue Na+; Tissue K+