Adhesion and Adhesives of Fungi and Oomycetes

Abstract

Many fungi adhere strongly to an outer surface of a host or a substratum before penetration; the ability to adhere is a virulence factor for plant and animal pathogens. Because substrata such as the plant cuticle are largely inert hydrophobic surfaces, plant pathogenic fungi often adhere to plastics. Strong adhesion is generally mediated by a secreted glue. Fungal glues are typically formed in an aqueous environment, and as such they may provide models for commercial glues, including for biomedical applications. The best-characterized fungal glue is a galactosaminogalactan polymer that serves as an adhesive to plastic, fibronectin, and epithelial cells in the mammalian pathogen Aspergillus fumigatus. However, most fungal glues are apparently mannoprotein(s). Despite our advances in fungal genomics, most fungal glues are uncharacterized, in contrast to the well-characterized fungal pathogen-mammalian host adhesins produced by Candida albicans; these adhesins, which bind to specific host receptors, are primarily large, glycosylphosphatidylinositol (GPI)-anchored cell wall mannoproteins that are posttranslationally covalently cross-linked to the cell wall β1,6-glucans. Adhesins typically have tandem repeats; adhesins such as the C. albicans ALS family bind to both specific cell types and to plastic. We postulate that the mannoprotein glues from plant pathogenic fungi are secreted in a more water-soluble form, are transiently sticky, and are cross-linked extracellularly. Anti-adhesive strategies may enable new plant disease control methods that are environmentally compatible because anti-adhesive strategies do not necessarily require any uptake of compounds into the fungus or disruption of a eukaryotic metabolic pathway.

Ralph Nicholson was deceased at the time of publication.