Changes in protein profile of Platycladus orientalis (L.) roots and leaves in response to drought stress

Platycladus orientalis (L.) Franco is widely used for afforestation in arid and semi-arid areas due to its high drought tolerance. To better understand the mechanism involved in drought tolerance in this important tree, responses to drought stress have been studied in 1-year-old P. orientalis via water withholding. Several physiological parameters were evaluated in four drought-treated groups. The root and leaf proteomes of two-dimensional electrophoresis (2-DE) gels were obtained, and a total of 162 proteins with significant quantitative variations and 1.5-fold differences in proteins were selected and identified by matrix-assisted laser desorption/ionization-time-of-flight/time-of-flight (MALDI-TOF/TOF) tandem mass spectrometry (MS/MS). The majority of identified proteins were classified into functional categories, including stress response/defense, carbohydrate metabolic process, nitrogen metabolism, proteolysis, and photosynthesis. The proteome results revealed that a series of strategies were employed to survive in the drought environment, such as the maintenance of protein stability, activation, and folding; reactive oxygen species (ROS) detoxification; the regulation of cell osmotic conditions and cell wall integrity; energy metabolism; and stabilization of the cell skeleton. One of the most prominent findings in this study was the number of bark protein-like proteins and heat shock proteins detected in both root and leaf tissues in drought stress conditions. In addition, 12 differentially expressed proteins were selected for quantitative reverse transcription PCR analysis; not all of the protein expression levels were consistent with the mRNA expression levels. Our data provide a comprehensive picture of the root and leaf responses under varying watering regimes, which could be beneficial for further research and for understanding highly complex drought stress responses.