Proteomic profiling of cellular targets of lipopolysaccharide-induced signalling in Nicotiana tabacum BY-2 cells

Plants constantly monitor for pathogen challenge and utilize a diverse array of adaptive defense mechanisms, including differential protein regulation, during pathogen attack. A proteomic analysis of Nicotiana tabacum BY-2 cells was performed in order to investigate the dynamic changes following perception of bacterial lipopolysaccharides. A multiplexed proteome analysis, employing two-dimensional difference-in-gel-electrophoresis with CyDye™ DIGE fluors, as well as Ruthenium II tris (bathophenanthroline disulfonate) fluorescence staining and Pro-Q^® Diamond phosphoprotein-specific gel staining, monitored over 1500 proteins and resulted in the identification of 88 differentially regulated proteins and phosphoproteins responsive to LPS_B.cep.-elicitation. Functional clustering of the proteins both at the level of their abundance and phosphorylation status, revealed 9 proteins involved in transport, ion homeostasis and signal transduction. A large number of responsive proteins were found to be involved in metabolism- and energy-related processes (36), representing various metabolic pathways. Another abundant category corresponded to proteins classified as molecular chaperones and involved in protein destination/targeting (12). Other categories of proteins found to be LPS_B.cep.-responsive and differentially regulated include cell structure- and cytoskeletal rearrangement proteins (8) and proteins involved in transcription and translation as well as degradation (11). The results indicate that LPS_B.cep. induces metabolic reprogramming and changes in cellular activities supporting protein synthesis, -folding, vesicle trafficking and secretion; accompanied by changes to the cytoskeleton and proteosome function. Many of the identified proteins are known to be interconnected at various levels through a complex web of activation/deactivation, complex formation, protein-protein interactions, and chaperoning reactions. The presented data offers novel insights and further evidence for the biochemical action of LPS_B.cep. as a resistance elicitor, a pathogen-associated molecular pattern molecule and triggering agent of defense responses associated with innate immunity.