Hydrophobins in the Life Cycle of the Ectomycorrhizal Basidiomycete Tricholoma vaccinum

Abstract

Hydrophobins—secreted small cysteine-rich, amphipathic proteins—foster interactions of fungal hyphae with hydrophobic surfaces, and are involved in the formation of aerial hyphae. Phylogenetic analyses of Tricholoma vaccinum hydrophobins showed a grouping with hydrophobins of other ectomycorrhizal fungi, which might be a result of co-evolution. Further analyses indicate angiosperms as likely host trees for the last common ancestor of the genus Tricholoma. The nine hydrophobin genes in the T. vaccinum genome were investigated to infer their individual roles in different stages of the life cycle, host interaction, asexual and sexual development, and with respect to different stresses. In aerial mycelium, hyd8 was up-regulated. In silico analysis predicted three packing arrangements, i.e., ring-like, plus-like and sheet-like structure for Hyd8; the first two may assemble to rodlets of hydrophobin covering aerial hyphae, whereas the third is expected to be involved in forming a two-dimensional network of hydrophobins. Metal stress induced hydrophobin gene hyd5. In early steps of mycorrhization, induction of hyd4 and hyd5 by plant root exudates and root volatiles could be shown, followed by hyd5 up-regulation during formation of mantle, Hartig’ net, and rhizomorphs with concomitant repression of hyd8 and hyd9. During fruiting body formation, mainly hyd3, but also hyd8 were induced. Host preference between the compatible host Picea abies and the low compatibility host Pinus sylvestris could be linked to a stronger induction of hyd4 and hyd5 by the preferred host and a stronger repression of hyd8, whereas the repression of hyd9 was comparable between the two hosts.

Seeking the Roles for Fungal Small-Secreted Proteins in Affecting Saprophytic Lifestyles

“…Another example of SSPs are hydrophobins are present across the fungal kingdom and have an ability to self-assemble into films at hydrophilic-hydrophobic interfaces (Wessels, 1996;Bayry et al, 2012). They have been found to be regulated during development of the ectomycorrhizal basidiomycete Tricholoma vaccinum and differentially expressed during the early steps of mycorrhization, in a manner that is dependent on host preference (Sammer et al, 2016). Hydrophobins and other effector-like proteins are also delivered during Trichoderma association with plants ( Ramírez-Valdespino et al, 2019).…”

Die Hydrophobine der Pilze – Vielzweckproteine mit Anwendungspotential

“…Sogar innerhalb einer Pilzart werden mehrere Mitglieder der Proteinfamilie gefunden, der bärtige Ritterling ( Tricholoma vaccinum, ein Basidiomycet) beispielsweise besitzt neun Hydrophobine kodierende Gene. Dass diese nicht alle gleichzeitig abgelesen werden, sondern einige nur in bestimmten Stadien des Lebenszyklus ihres Produzenten, spricht für unterschiedliche Funktionen der einzelnen Hydrophobine . Andererseits sind sich die Hydrophobine bezüglich ihrer physikochemischen Eigenschaften insgesamt ähnlich, deshalb kann in manchen Fällen ein Hydrophobin beim Funktionsausfall eines anderen einspringen.…”

Fungal Genomes and Insights into the Evolution of the Kingdom

“…Producing and orienting spore forming structures at the right time of day can maximize the probability that offspring will be dispersed and establish the next generation. Genes encoding hydrophobin proteins, which are important for fruiting body development in mushrooms, are also expanded in copy number in Agaricomycotina species [152–155]. The p450 monoxygenase family is also highly expanded in mushroom-forming fungi, especially in white rot fungi such as Phanerochaete , which likely allow it to degrade a rich collection of substrates including lignin [63,152,156].…”