Cellulolytic enzymes of the obligately biotrophic rust fungus Uromyces viciae-fabae are regulated differentiation-specifically

Abstract

Uredospores of the obUgately biofrophic broad bean rust fungus Uromyces viciae-fabae form infection structures on artificial membranes providing a thigmotropic signal. In nalure these are essential for invasion of the host plant through the stomata. '[his experimental system was used to analyse the production of cellulolytic enzymes duting the differentiation of rust infection stru~lures.Low .cellulase activity was detected in dormant spores and in germ tubes. Enzyme activity increased duting appressorium development and reached a maximum when infection hyphae and haustorial mother cells were formed. Seven cellulolytic enzymes were separated by chromatofocusing on DEAE = Si500 and PBE 94 exchangers. At least two cellulases, characterized by isoelectric points of 7' I and 7'3, were identified as endo-eellulases. The neutral enzyme forms increased from 3'3 % of the total activity at appressorium formation to 36'6% when infection hyphae were formed (18 h p.i.), and to 45'4% in haustorial mother cells (24 h p.i.). Cellulase activity of the rust' fungus is neither substrate-inducible nor catabolite repressible. The regulation of these enzymes appears to be strictly controlled by the differentiation of infection struclures, and is therefore distinct from cellulases of necrotrophs and saprophytes investigated thus far.

Regulation of pectin methylesterase and polygalacturonate lyase activity during differentiation of infection structures in Uromyces viciae-fabae

“…However, little is known about the regulation of these enzymes in obligately biotrophic fungi. In previous reports (Frittrang e t al., 1992;Heiler et a/., 1993) and in this paper we have demonstrated that the broad bean rust fungus forms cell-wall-degrading enzymes mainly during the time when infection hyphae and haustorial mother cells are differentiated. This differentiation-specific pattern of enzyme formation may explain why cell-wall-degrading enzymes of rust fungi have been overlooked and why their potential role in the infection process has not been recognized .…”

“…their synthesis requires fungal morphogenesis but not the presence of substrate, and is not subject to catabolite repression. The acidic cellulases start to appear during appressorium development (Heiler et al, 1993), while the formation of PME isoforms B1 and B2 (PIS 5.2 and 5.6) begins with differentiation of young infection hyphae, which are usually enlarged to substomatal vesicles ; Fig. 4).…”

“…At late stages of infection structure development, i.e. when infection hyphae and haustorial mother cells are formed, the neutral endocellulases (PIS 7.1 and 7.3;Heiler et al, 1993) and the basic PME isoform A (PI 8.2; Frittrang et al, 1992) are present and these enzymes, like PL, should be tightly bound to the plant cell wall at the site of penetration. For localized wall degradation, both a tight binding and a pH shift towards alkaline conditions would be important.…”

Targeted Cell Wall Degradation at the Penetration Site of Cowpea Rust Basidiosporelings

“…The dikaryotic urediospores of U. viciae-fabae secrete a number of cell-wall-degrading enzymes in a highly regulated manner. Cellulase production occurs already during appressorium formation (Heiler et al 1993), pectinmethylesterases are secreted during infection hypha development, and polygalacturonate lyase is produced during differentiation of haustorial mother cells (Deising et al 1995). Thus, the fungus seems to be adapted to the specific infection conditions found during stomatal penetration and subsequent host cell penetration.…”

The Uredinales: Cytology, Biochemistry, and Molecular Biology

“…Acidic and neutral cellulase (Heiler et al 1993), extracellular protease (Rauscher et al 1995), chitin deacetylase (Deising and Siegrist 1995), pectin esterase (Frittrang et al 1992), pectin methylesterase (Deising et al 1995a), neutral cellulase (Heiler et al 1993), and polygalacturonate lyase (Deising et al 1995a) activities were found (Fig. 4.5).…”