Effect of Medicago sativa Mhb1 gene expression on defense response of Arabidopsis thaliana plants

Besides the previously described nitric oxide-detoxification activity we identified new features of class-1 non-symbiotic hemoglobin from Medico go sativa (Mhbl). Under in vitro conditions, using peroxidase in-gel activity assay, the Mhbl protein was shown to possess also peroxidase-like activity. Due to this activity, in the presence of nitrite and hydrogen peroxide, the protein can mediate autonitration and nitration of other proteins at tyrosine residues, as revealed by tandem mass spectrometry and immune assay approaches. Mhbl through its multifunctional activities can affect different components of signal transduction cascades operating during plant response to infections. This influence is manifested by Mhbl-mediated selective up-regulation of expression of certain pathogen inducible genes in Pseudomonas syringae infected Arabidopsis thaliana plants which overproduce Mhbl, as revealed by reverse transcription-quantitative real-time PCR analysis. Changes in expression level of these genes can influence such processes as synthesis of secondary metabolites, protein degradation and biosynthesis of ethylene. They can also result in alteration of pathogen-induced defense response of Mhbl transgenic plants.