Protein phosphorylation in Nicotiana tabacum cells in response to perception of lipopolysaccharides from Burkholderia cepacia

The perception mechanism of cultured Nicotiana tabacum cells towards lipopolysaccharides (LPS) from Burkholderia cepacia was investigated with regard to the role of protein phosphorylation during signal perception-related responses. The results obtained in this study provide evidence that B. cepacia LPS has specific effects on reversible protein phosphorylation events underlying the perception systems involved in the interaction of plant cells with LPS and as such, contribute to the understanding of LPS as a 'resistance elicitor' or possible triggering agent of innate immunity. Bacterial LPS have the ability to act as modulators of the innate immune response in plants. Complex and largely unresolved perception systems exist for LPS on the plant cell surfaces that lead to the activation of multiple intracellular defense signaling pathways. The aim of the present study was to investigate the perception mechanism of cultured Nicotiana tabacum cells towards LPS from Burkholderia cepacia (LPS _B.cep.), with regard to the role of protein phosphorylation during signal perception-related responses to gain a better understanding of the chemosensory perception of LPS elicitor signals in plant cells. In vivo labeling of protein phosphorylation events during signal transduction indicated the rapid phosphorylation of several proteins with the hyperphosphorylation of two proteins of 28 and 2 kDa, respectively. Significant differences and de novo LPS-induced phosphorylation were also observed with two-dimensional analysis. The protein kinase inhibitor, staurosporine, totally inhibited the extracellular alkalinization response induced by LPS _B.cep., while the oxidative burst was only partially inhibited by staurosporine. Inhibition of protein phosphatase activity by calyculin A intensified the LPS _B.cep. responses. The results indicate that perception- and signal transduction responses during LPS _B.cep. elicitation of tobacco cells require a balance between the actions of certain protein kinases and protein phosphatases.