Quantitative Proteomics Analysis Of Soybean Leaves And Roots During The Initial Stage Of Salt Stress

Salt stress is one of the major abiotic stresses affecting plant development, productivity and growth of crops all over the world. How to improve plant salt stress tolerance and make better use of the salinity soil has become a focus of plant biology research. Soybean has high nutritional value and economic value as one of an important oil crops in the world, which is a kind of moderately salt-tolerant organisms. Thus, it is of great importance to study the mechanisms of soybean salt tolerance, and to screen key salt stress responsive proteins(genes), which will have an important influence on soybean molecular breeding and cultivation of salt-tolerant soybean varieties.In this study, soybean cultivar Dong Nong 50 was used as plant material. Mophological and physiological changes were analyzed to soybean seedlings subjected to 200 mM NaCl during the first 48 h of treatment time. Several phyisological characteristics such as chlorophyll content s of soybean leaves, malonaldehyde contents, superoxide dismutase activities and peroxidase activities as well as the ratio of sodium and potassium ion contents in soybean roots and leaves were studied. The results showed that at the high concentration of salt treatment, the soybean leaves and roots respond to salt stress by enhancing the activities of antioxidant enzymes. We also found that activities of antioxidant enzymes reached the climax when treated for 12 h.To further analyze the molecular mechanisms of early response of soybean seedling to salt stress, an i TRAQ-based proteomic approach was used to investigate the proteomes of soybean leaves and roots under 12 h of 200 mM Na Cl treatment. Three independent biological replicates were performed. These MS data are available via Proteome Xchange with the identifier PXD002851. In total, 6610 proteins were identified after LC-MS/MS analysis. To be identified as being significantly differentially expressed, a protein should be quantified with at least three peptides in each experimental replicate, a p-value smaller than 0.05 and fold change greater than 1.3 or less than 0.7. Based on these criteria, 278 DEPs were identified in soybean leaves, of which 237(85.3%) displayed increases, and 41(14.7%) displayed decreases in abundance under salt stress conditions; at the same time, 440 DEPs were identified in soybean roots, of which 354(80.5%) showed an increase, and 86(19.5%) showed a decrease in abundance after salt stress treatment. On the basis of the BLAST alignment, Gene Ontology, and information from the literature, all these identified DEPs in leaves and roots were classified into 13 functional categories: photosynthesis and carbohydrate metabolism, metabolism, stress and defence, transcription related, protein synthesis, protein folding and transporting, protein degradation, signaling, membrane and transport, cell structure, cell division/differentiation and fate, miscellaneous and unknown. The most represented DEPs in soybean leaves were associated with pho tosynthesis and carbohydrate metabolism(24.1%), metabolism(14.4%) and protein synthesis(13.3%); the root DEPs in these first two categories were same as in leaves, while the third category was transcription related proteins(10.2%). In soybean leaves, there were only 8 DEPs related to stress and defence, whereas the number of DEPs in this category in roots was 37, and most of which showed increased levels under salt treatment. Proteins related to stress signal transduction as well as membrane and transport proteins in soybean were analysed at the early stages of salt stress treatment. Besides, the numbers of DEPs belonging to the categories of transcription related, metabolism and protein degradation were largely different between the leaves and the roots under salt treatment. Moreover, protein-protein interaction analysis revealed that proteins involved in metabolism, carbohydrate and energy metabolism, protein synthesis and redox homeostasis could be assigned to four high salt stress response networks.Furthermore, semi-quantitative RT-PCR analysis revealed that some of the proteins, such as a 14-3-3, MMK2, PP1, TRX-h, were also regulated by salt stress at the level of transcription. These results indicated that effective regulatory protein expression rel ated to signalling, membrane and transport, stress defense and metabolism all played important roles in the short-term salt response of soybean seedlings. The mechanisms of soybean responses to salt stress has been supplemented.