Fusarium verticillioides and related species of the Gibberella fujikuroi complex secrete an endopolygalacturonase not inhibited by Monocot PGIPs

Fusarium verticillioides, like others fungal species of the Gibberella fujikuroi complex, is a toxigenic and pathogenic species able to produce disease on important monocot crops. In order to understand the involvement of the endopolygalacturonase (endo-PG) of F. verticillioides in the infection process we have purified the endo-PG produced in culture by four different isolates of this fungus and cloned the corresponding genes. The purified endo-PGs showed quite identical biochemical and molecular properties. In particular, all endo-PGs were not inhibited by polygalacturonase-inhibiting proteins (PGIPs) extracted from monocot host plants (like aparagus and maize) and were partially inhibited by bean PGIP, but only when used in the assay at extraordinarily high doses. The deduced aminoacidic sequence of endo-PG was quite identical among the different isolates of F. verticillioides, and was similar to those obtained from endo-PGs of seven other species of the G. fujikuroi complex (F. sacchari, F. fujikuroi, F. proliferatum, F. subglutinans, F. thapsinum, F. nygamai, F. circinatum). These endo-PGs, like that of F. verticillioides, were also insensitive to inhibition by monocot PGIP whilst were inhibited at various degree by the bean PGIP. The multiple alignement of the endo-PG sequences permitted to identify the peculiar aminoacidic substitutions of the different fungal enzymes that are likely involved in the binding with the bean PGIP.