Proteomic Response of Sugar Beet Monosomic Addition Line M14 Guard Cells to Salt Stress

Abstract Background Soil salinity is one of the most detrimental abiotic stresses that limit crop production and threaten global food security. The responsiveness of stomatal guard cells to various stimuli is important for plants to balance transpirational water loss and carbon dioxide (CO2) intake for photosynthesis. It is important to identify differences in proteomic changes under salt stress and to understand the mechanisms underlying salt stress-induced stomatal movement in sugar beet guard cells through proteomic analysis. Results In this study, we observed stomatal closure and changes in ascorbate peroxidase activities during short-term salt stress treatment of sugar beet monosomic addition line M14. We analyzed proteomic changes in guard cells in response to the salt stress using an iTRAQ-based quantitative proteomic approach. A total of 142 proteins were differentially changed in guard cells by the salt stress treatment. They include several ribosomal proteins, metabolic enzymes and photosystem-related proteins. Gene ontology (GO) annotation of the differentially abundant proteins highlights most of the proteins are related to binding activity, response to stimuli, and glutathione metabolism, phenylpropanoid biosynthesis and carbon fixation pathways. Many of the proteins were targeted to the chloroplast, nucleus and cell wall. They may play an important role in the process of stomata closure. In addition, several antioxidant enzymes (e.g., peroxidase, ascorbate peroxidase and dehydroascorbate reductase) involved in the regulation of ROS homeostasis were identified. Transcriptional levels of 16 differential proteins involved in stress responses did not correlate well with the protein levels, indicating different regulatory mechanisms in guard cells. Conclusions The proteomics results have revealed interesting mechanisms underlying the sugar beet guard cell response to salt stress, which have not been reported before. The knowledge may facilitate molecular breeding and/or engineering efforts toward enhancing crop stress tolerance while not compromising yield.