Identification of Drought-induced Leaf Proteomes in Switchgrass

This study was performed to construct a protein interactive network associated with drought stress in Switchgrass (Panicum virgatum). A ‘Sandwich’ system (potting mix-perlite-potting mix) was constructed to grow Switchgrass ‘Alamos’. Drought treatment was applied by withholding watering until the soil moisture monitored by GS3 sensors at 20cm depth dropped below 5% VWC. Water-use efficiency measured using LI-COR 6400 Portable-Photosynthesis-System showed significant difference between treated and control. Leaf proteins were extracted from the top three fully expanded leaves. Half of the leaf protein extract was treated with ProteoMiner to remove high-abundant proteins. Both treated and untreated proteins labeled with 8-plex iTRAQ were analyzed by LC-MS/MS using Orbitrap Elite hybrid mass spectrometer. Proteins were identified using the MS data to query the Switchgrass annotated database. Of the 5505 proteins identified from the total leaf protein, 232 showed significant difference between treated and control, 74 were down-regulated (fold <0.6) and 159 were up-regulated (fold >1.7). In the protein after ProteoMiner depletion, 4949 total proteins were identified, 127 were identified as significantly changed proteins with 31 down-regulated and 98 up-regulated. Using NCBI conserved domain search, the ProteoMiner treatment resulted in identification of higher number of low-abundance proteins such as transcriptional factors (WCOR413). The fold change values were consistent for proteins identified from both ProteoMiner treated and untreated samples, such as proteins in the carbohydrate metabolism pathway. The drought-induced protein changes are confirmed using physio-biochemical analyses. Growth models for the respective species under drought conditions are being developed to associate molecular changes with agronomic characteristics.