BackgroundTibetan wild barley (Hordeum spontaneum L.) has been confirmed to contain elite accessions in tolerance to abiotic stresses, including salinity. However, molecular mechanisms underlying genotypic difference of salt tolerance in wild barley are unknown.ResultsIn this study, two Tibetan wild barley accessions (XZ26 and XZ169), differing greatly in salt tolerance, were used to determine changes of ionomic, metabolomic and proteomic profiles in the shoots exposed to salt stress at seedling stage. Compared with XZ169, XZ26 showed better shoot growth and less Na accumulation after 7 days treatments. Salt stress caused significant reduction in concentrations of sucrose and metabolites involved in glycolysis pathway in XZ169, and elevated level of tricarboxylic acid (TCA) cycle, as reflected by up-accumulation of citric acid, aconitic acid and succinic acid, especially under high salinity, but not in XZ26. Correspondingly, proteomic analysis further proved the findings from the metabolomic study.ConclusionXZ26 maintained a lower Na concentration in the shoots and developed superior shoot adaptive strategies to salt stress. The current result provides possible utilization of Tibetan wild barley in developing barley cultivars for salt tolerance.Electronic supplementary materialThe online version of this article (doi:10.1186/s12864-016-3242-9) contains supplementary material, which is available to authorized users.

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Calcium (Ca 21) signaling modulates sodium (Na 1) transport in plants; however, the role of the Ca 21 sensor calmodulin (CaM) in salt tolerance is elusive. We previously identified a salt-responsive calmodulin (HvCaM1) in a proteome study of barley (Hordeum vulgare) roots. Here, we employed bioinformatic, physiological, molecular, and biochemical approaches to determine the role of HvCaM1 in barley salt tolerance. CaM1s are highly conserved in green plants and probably originated from ancestors of green algae of the Chlamydomonadales order. HvCaM1 was mainly expressed in roots and was significantly up-regulated in response to long-term salt stress. Localization analyses revealed that HvCaM1 is an intracellular signaling protein that localizes to the root stele and vascular systems of barley. After treatment with 200 mM NaCl for 4 weeks, HvCaM1 knockdown (RNA interference) lines showed significantly larger biomass but lower Na 1 concentration, xylem Na 1 loading, and Na 1 transportation rates in shoots compared with overexpression lines and wild-type plants. Thus, we propose that HvCaM1 is involved in regulating Na 1 transport, probably via certain class I high-affinity potassium transporter (HvHKT1;5 and HvHKT1;1)-mediated Na 1 translocation in roots. Moreover, we demonstrated that HvCaM1 interacted with a CaM-binding transcription activator (HvCAMTA4), which may be a critical factor in the regulation of HKT1s in barley. We conclude that HvCaM1 negatively regulates salt tolerance, probably via interaction with HvCAMTA4 to modulate the downregulation of HvHKT1;5 and/or the up-regulation of HvHKT1;1 to reduce shoot Na 1 accumulation under salt stress in barley.

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