Ionomic, Metabolomic and Proteomic Analyses Reveal Molecular Mechanisms of Root Adaption to Salt Stress in Tibetan Wild Barley

In our previous study, Tibetan wild barley (Hordeum spontaneum L.) has been found to be rich in the elite accessions with strong abiotic stress tolerance, including salt stress tolerance. However, the molecular mechanism of salt tolerance underlying the wild barley remains to be elucidated. In this study, two Tibetan wild barley accessions, XZ26 (salt-tolerant) and XZ169 (salt-sensitive), were used to investigate ionomic, metabolomic and proteomic responses in roots when exposed to 0, 200 (moderate) and 400 mM (high) salinity. XZ26 showed stronger root growth and maintained higher K concentrations when compared with XZ169 under moderate salinity, while no significant difference was found between the two accessions under high salinity. A total of 574 salt-regulated proteins and 153 salt-regulated metabolites were identified in the roots of both accessions based on quantitative proteomic (iTRAQ methods) and metabolomic (GC-TOF/MS) analysis. XZ26 developed its root adaptive strategies mainly by accumulating more compatible solutes such as proline and inositol, acquiring greater antioxidant ability to cope with ROS, and consuming less energy under salt stress for producing biomass. These findings provide a better understanding of molecular responses of root adaptive strategies to salt stress in the wild barley.