Thylakoid proteome variation of Eutrema salsugineum in response to drought and salinity combined stress

It is well known that plant responses to stress involve different events occurring at different places of the cell/leaf and at different time scales in relation with the plant development. In fact, the organelles proteomes include a wide range of proteins that could include a wide range of proteins showing a considerable change in cellular functions and metabolism process. On this basis, a comparative proteomics analysis and fluorescence induction measurements were performed to investigate the photosynthetic performance and the relative thylakoid proteome variation in Eutrema salsugineum cultivated under salt stress (200 mM NaCl), water deficit stress (PEG) and combined treatment (PEG + NaCl) as a hyperosmotic stress. The obtained results showed a significant decrease of plant growth under drought stress conditions, with the appearance of some toxicity symptoms, especially in plants subjected to combined treatment. Application of salt or water stress alone showed no apparent change in the chlorophyll a fluorescence transients, primary photochemistry (fluorescence kinetics of the O-J phase), the PQ pool state (J-I phase changes), (Fv/Fm) and (Fk/Fj) ratios. However, a considerable decrease of all these parameters was observed under severe osmotic stress (PEG + NaCl). The thylakoid proteome analysis revealed 58 proteins showing a significant variation in their abundance between treatments (up or down regulation). The combined treatment (PEG + NaCl) induced a decrease in the expression of the whole PSII core subunit (D1, D2, CP43, CP47, PsbE and PsbH), whereas the OEC subunits proteins remained constant. An increase in the amount of PsaD, PsaE, PsaF, PsaH, PsaK and PsaN was detected under drought stress (PEG5%). No significant change in the accumulation of Cyt b6 and Cyt f was observed. Some regulated proteins involved in cellular redox homeostasis were detected (glutamine synthetase, phosphoglycerate kinase, transketolase), and showed a significant decrease under the combined treatment. Some oxidative stress related proteins were significantly up-regulated under salt or drought stress and could play a crucial role in the PSI photoprotection and the control of ROS production level.