Molecular characterization of an endopolygalacturonase from Fusarium oxysporum expressed during early stages of infection

The tomato vascular wilt pathogen Fusarium oxysporum f. sp. lycopersici pro duces an array of pectinolytic enzymes that may contribute to penetration a nd colonization of the host plant. Here we report the isolation of pg5, enc oding a novel extracellular endopolygalacturonase (endoPG) that is highly c onserved among different formae speciales of F. oxysporum. The putative mat ure pg5 product has a calculated molecular mass of 35 kDa and a pi of 8.3 a nd is more closely related to endoPGs from other fungal plant pathogens tha n to PG1, the major endoPG off. oxysporum. Overexpression of pg5 in a bacte rial heterologous system produced a 35-kDa protein with endoPG activity. Ac cumulation of pg5 transcript is induced by citrus pectin and D-galacturonic acid and repressed by glucose. As shown by reverse transcription-PCR, pg5 is expressed by F. oxysporum in tomato roots during the initial stages of i nfection. Targeted inactivation of pg5 has no detectable effect on virulenc e toward tomato plants.