Immunocytochemical studies of the infection mechanisms of Botrytis fabae II. Host cell wall breakdown

Abstract

Immunoelectron microscopy using the anti-pectin monoclonal antibody JIM 7 confirmed earlier observations that pectin degradation is a primary event in the process of host cell wall breakdown during the development of chocolate spot disease (causal agent : Botrytis fabae (Sard.)) of broad bean. Close examination of infected and noninfected Vicia faba L. leaves indicated a loss of JIM 7-labelling, and therefore, methyl-esterified pectin, from swollen walls of infected and contiguous epidermal cells. Modified mesophyll walls also possessed less methylesterified pectin than healthy walls. Enzymes which attack methyl-esterified pectin appeared to be most active in regions of host tissue close to sites of fungal infection.Ultrastructural studies using the enzyme, cellobiohydrolase conjugated to gold (CBH1-Au) revealed that the cellulose microfibrils of outer epidermal walls of non-infected V. faba leaf tissue were heavily masked by other components of the plant cell wall. Such material was most probably pectin because the cellulose microfibrils of swollen epidermal and modified mesophyll walls of infected host tissue were heavily labelled with CBH1-Au. These results were confirmed by double-labelling studies using JIM 7 and CBH1-Au. At early stages of the infection process, limited cellulose degradation was observed in infected leaf tissue. Double-labelling experiments using the monoclonal antibody BC-KH4 directed against Botrytis matrices and a marker for the plant cell wall (JIM 7 or CBH1-Au) confirmed previous observations that the fungal matrices extended through modified host walls and degenerate cytoplasm. It is suggested that the wall-modifying action of the pectin-degrading enzymes produced during the infection process might facilitate pervasion of matrix material associated with the infection hyphae through host cell walls. Possible role(s) of such matrix material during the post-penetration processes of the V. faba-B. fabae relationship are discussed.

Immunocytochemical studies of the infection mechanisms of Botrytis fabae I. The fungal extracellular matrix in penetration and post‐penetration processes

“…fabae interface inside the host tissue, immunolabelled matrix material could be seen to extend through the swollen epidermal and mesophyll cell walls. The mechanism of plant cell wall breakdown and the role of B. fabae extracellular matrices in this process is the subject of the accompanying paper (Cole, Dewey & Hawes, 1998).…”

Overexpression of Pectin Methylesterase Inhibitors in Arabidopsis Restricts Fungal Infection by Botrytis cinerea

“…However, given the effect of pectin methylesterification on the physicochemical properties of the walls, they may also have a role in defense against pathogens by influencing the susceptibility of the wall to cell walldegrading enzymes, which in some cases have a major role in pathogenesis (Clark and Lorbeer, 1976;Collmer and Keen, 1986;Cole et al, 1998;De Lorenzo et al, 2001;D'Ovidio et al, 2004). Pectin hydrolysis often occurs in the diseases caused by soft rot bacteria and fungi and appears to be the prerequisite for degradation of other cell wall components (D'Ovidio et al, 2004).…”

Counteracting virulence mechanisms of grain legume pathogens

“…These authors showed that cowpea rust (Uromyces vignae) penetrated the cell walls of the non-host, V. faba and that a zone of the plant wall, 0.2 μm wide along the fungal penetration hypha, had reduced pectin and xyloglucan. Similarly, Cole et al (1998) showed by immunoelectron microscopy, using the anti-pectin monoclonal antibody JIM 7, that pectin degradation is a primary event in host cell wall breakdown during the development of chocolate spot of V. faba caused by B. fabae.…”