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

Abstract

The broad bean rust fungus Uromyces viciae-fabae differentiates infection structures up to the haustorial mother cell stage on thigmotropically inductive membranes in the absence of its host plant. Formation of pectin methylesterase (PME) and polygalacturonate lyase (PL), potentially involved in host cell wall degradation, was studied during infection structure differentiation by this biotrophic fungus. PME was first detectable when substomatal vesicles were formed and reached a maximum when infection hyphae and haustorial mother cells were differentiated. Four isoenzymes, exhibiting pls of 82,506, 5-2 and 45, were separated by chromatofocusing, and the kinetics of their synthesis and the K,s of the three major isoenzymes were determined. The enzyme activity was formed independently of the presence of its substrate and its regulation was thus differentiation-specific. A single PL was induced when haustorial mother cells were formed and i t s synthesis appeared to be controlled by both the developmental stage of infection structures and the availability of its substrate. Polygalacturonate concentrations lower than 0-025 mg ml-l induced enzyme synthesis, and at 0 2 5 mg ml-l the induction process appeared to be saturated. Enzyme formation in the presence of 50 mM glucose, fructose or sucrose suggested that neither pectic enzyme was subject to catabolite repression. Significant proportions of PME (approx. 57%) and PL (approx. 7 6 % ) activity were located extracellularly in 24-h-old differentiated infection structures and could contribute to the establishment of the parasite. Physico-chemical and kinetic properties of the enzymes and associated alterations of the apoplastic pH of infected host plants appeared to be important factors in the success of infection and could explain the restriction of cell wall damage at the penetration site usually observed in interactions involving obligately biotrophic fungi.Germany

Role of cell wall degrading enzymes in the interaction of poplar and Melampsora larici-populina Kleb.

“…Cellulase production occurs already during appressorium formation. Pectin methylesterases are secreted during hypha development, and polygalacturonate lyase is produced during differentiation of haustorial mother cells (Heiler et al, 1993;Deising et al, 1995). In our study, we also found that in the M. larici-populina and poplar cultivars interaction, the peak value of ΔPMG appeared in 1 dpi and 5 dpi both in susceptible and resistant cultivars.…”

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.…”

“…This suggests that although turgor pressure may support penetration, enzymes seem to play a major role. However, since Uromyces is a biotrophic pathogen fed by haustoria that the fungus produces within living plant cells, enzyme secretion should be very restricted during the penetration process (Deising et al 1995). Therefore, this study was undertaken to investigate if and how far the wall at the penetration site of Uromyces vignae Barclay shows signs of enzymatic degradation.…”

Cloning and Sequence Analysis of Endopolygalacturonase Genes in Venturia nashicola and Venturia pirina

“…A study examining the pectin-degrading enzymes for obligate or biotrophic pathogens such as bean rust fungus Uromyces viciae-fabae 8 , lettuce downy mildew pathogen Bremia lactucae 48 , wheat powdery mildew fungus Blumeria graminis f. sp. tritici 43 , and apple scab fungus Venturia inaequalis 47 , has also been initiated.…”