Molecular identification and expression of the peroxidase responsible for the oxidative burst in French bean (Phaseolus vulgaris L.) and related members of the gene family

Molecular characterization has been accomplished for five members of the pe roxidase gene family in French bean. The most important of these, designate d FBP1, corresponds to the isoform believed to be responsible for the apopl astic oxidative burst demonstrated by suspension-cultured cells in response to fungal elicitor. Identification was made by a complete match of six pep tide sequences derived from the native protein to the translated sequence o f the cDNA. Modelling of the surface structure in comparison with two other members of the peroxidase family did not reveal any unusual features which might account for its role in the oxidative burst. However, FBP1 when expr essed in Pichia pastoris generated H2O2 using cysteine at pH 7.2, a specifi c property of the native protein when isolated from suspension-cultured cel ls. FBP1, together with other members of the family, were all induced in ce ll cultures by elicitor action although they all showed some expression in non-induced cultured cells. They were also expressed in all tissues examine d with varying levels of intensity of detection in northern blots. This was confirmed by in situ hybridization and FBP1 expression was confirmed in ti ssues where it has been previously detected by immunolocalization methods. Assigning roles to individual peroxidases is an important goal and molecula r identification of the oxidative burst peroxidase allows further explorati on of the relative roles of the different systems involved in generating re active oxygen species.