Comprehensive proteomic analysis revealing multifaceted regulatory network of the xero-halophyte Haloxylon salicornicum involved in salt tolerance

Haloxylon salicornicum is a xero-halophyte which grow predominantly in dry saline areas. However, the proteomic approach for revealing the regulatory network involved in salt adaptation of this important xerohalophyte has not been studied so far. In the present investigation, the label-free quantitative proteomic analysis was carried out in shoot of H. salicornicum to get an insight into the functional network of proteins involved in salt tolerance. Comparative proteomic analysis in control and salt treated plants of H. salicornicum by nano-ESI-LC-MS and MS/MS, and data base searching led to the identification of 723 proteins. Pathway enrichment analysis by KEGG uncovered various biological pathways to which salinity induced differentially regulated proteins are involved. In H. salicornicum, out of 723 identified proteins, 187 proteins were differentially regulated in response to salinity. In addition to significant up-regulation of stress responsive proteins, other proteins involved in carbohydrate metabolism, TCA cycle, protein synthesis, antioxidative defense systems, energy transfer, ion transport, nucleotide binding, and proteosomal proteins also significantly up-regulated under salinity in H. salicornicum. The major photosynthetic proteins up-regulated were RuBisCo, D1 protein, photosystem II-CP47, and cytochrome b599. TCA cycle component proteins such as citrate synthase, succinate dehydrogenase, and malate dehydrogenase upregulated indicating their significant roles in providing vital energy for salinity tolerance. Salinity induced higher expressions of ion transporters in H. salicornicum suggest efficient compartmentalization of toxic sodium ions. In addition, up-regulation of antioxidative defense system can be correlated with effective scavenging of salinity induced ROS, hence imparting salt tolerance. In H. salicornicum, protein synthesis was boosted under salinity as confirmed from the salinity-induced up-regulation of the ribosome associated proteins. Salinity induced significantly changed proteins of the ribosomal pathway include ribosomal protein components such as elongation factor-Tu (EF-Tu), initiation factor 1 and 2 (IF1, 2), Rpo cluster C and B, etc. Functional integrity of protein synthesis machinery in H. salicornicum is maintained under high salinity by higher abundance of ribosomal subunit proteins in NaCl-treated plants. We assume that consistent energy supply by the up-regulation of TCA cycle along with uninterrupted protein synthesis and maintenance of structural integrity of the photosynthetic machinery are the primary mechanism of salinity tolerance of H. salicornicum. In the present study, we comprehensively elucidated possible mechanisms associated with systematic salt tolerance of H. salicornicum employing proteomic approach. The information from this study will contribute to the genetic improvement of crop plants that can be grown in saline marginal lands.