Study On Tamarix Hispida Root Differentially Expressed Protein Under NaHCO₃ Stress

Soil salinization is one of the most important abiotic limiting factors which seriously affects plant growth, development and regional distribution. The area with soil salinization in our country is about 1 million ha, and it is an effective way to solve the problem of soil salinization by using molecular breeding method to improve the salt tolerance and cultivate novel salt-tolerant varieties. Tamarix hispida Willd. has strong salt-resistant ability. It can grow in 0.5%-l%saline, which is a fine species in improvement of saline.In this study, T. hispida was treated with 0.3M sodium bicarbonate for Oh,12h,24h and 48h respectively, and the differential expression proteins of T. hispida roots responding to salt were separated and identified using iTRAQ-MS/MS analysis under different treatment time. The function of differential expression proteins were analyzed further, which provided the theoretical basis for investigating the molecular mechanism on the response of tamarix to salt stress, and also provided rich data for illuminating the mechanism of salt tolerance in saline woody plants.In this study,521 differentially expressed proteins were identified. There were 294,263, and 166 proteins significantly differentially expressed after stress for 12,24, and 48 h, respectively.151,124 and 78 differentially expressed proteins were up-regulated and 143,139 and 88 differentially expressed proteins were down-regulated upon NaHC03 stress for 12,24 and 48 h, respectively.The results showed 43 proteins were found to be differentially regulated at all the three time points. We found that the function of protein mainly concentrated on active oxygen scavenging, stress and defense signal, and protein synthesis and degradation. This indicates that T. hispida can enhance the scavenging ability of active oxygen, the stress and defense signal, and the cell wall synthesis to improve the salt tolerance of T. hispida.GO analysis of differentially expressed proteins shows that analysis of differential proteins in the molecular function mainly concentrated in catalytic activity and binding, in cells mainly exist in the cell and organ, in biological processes of metabolism, cellular processes and metabolic process plays a major role of protein function.The research showed that numerous proteins of active oxygen scavenging were up-regulated expression, which indicated that scavenging action of active oxygen was the one of important ways for tamarix to defend the damage of active oxygen from salt stress. The abundance of protein related to signal transduction were regulated under salt stress to transduct the stress signal and regulate the stress resistance gene, which showed that signal transduction and gene expression were two ways on the defense of salt stress for T. hispida. Many protein related to metabolism were up-regulated under salt stress, which suggested that tamarix can regulate the ability of resistance to salinity through some metabolic pathways.By analyzing the results of quantitative PCR, we observed a positive correlation of r=0.433** when all significantly changed mRNAs with a cognate protein were considered is of the same direction of the change. Interestingly, a negative correlation of r=-0.269* was observed between proteins and mRNAs for the opposite direction of the change. We also found that the function of protein having same expression tendency concentrated on stress and defense signal, pH and osmotic equilibrium, active oxygen scavenging, G protein signal, in which the protein that participated in stress and defense signal was the most. The function of protein that had opposite expression tendency mainly concentrated on pH and osmotic equilibrium, protein synthesis, active oxygen scavenging, chromosome assemble and transcription, stress and defense signal, in which the protein on pH and osmotic equilibrium was the most.In this experiment, we further compared the changes of differential expressed protein with their cognate transcript level based on the data from tamarix transcriptome. The results showed that there were 50,86, and 42 differential expressed proteins of T. hispida roots changing in transcriptional level respectively when they were treated by sodium bicarbonate for 12,24 and 48 hours, and there was greatly significant correlation between the differential expressed protein and their cognate transcript level at the same or opposite direction of the change. This indicates that the expression level of mRNAs is not always associated with proteins level. The relationship between proteins and their cognate mRNAs is different in different pathway. The proteins and mRNAs with the same direction of the abundance change are related to cell wall synthesis, while the proteins and mRNAs with the opposite direction of the abundance change are related to active oxygen scavenging.