Ectomycorrhiza development involves the differentiation of structurall
y specialized fungal tissues (e.g., mantle and Hartig net) and an inte
rface between symbionts. Polypeptides presenting a preferential, up-,
or down-regulated synthesis have been characterized in several develop
ing ectomycorrhizal associations. Their spatial and temporal expressio
ns have been characterized by cell fractionation, two-dimensional poly
acrylamide gel electrophoresis, and immunochemical assays in the Eucal
yptus spp. Pisolithus tinctorius mycorrhizas. These studies have empha
sized the importance of fungal cell wall polypeptides during the early
stages of the ectomycorrhizal interaction. The increased synthesis of
30- to 32-kDa acidic polypeptides, together with the decreased accumu
lation of a prominent 95-kDa mannoprotein provided evidence for major
alterations of Pisolithus tinctorius cell walls during mycorrhiza form
ation. Differential cDNA library screening and shotgun cDNA sequencing
were used to clone symbiosis-regulated fungal genes. Several abundant
transcripts showed a significant amino acid sequence similarity to a
family of secreted morphogenetic fungal proteins, the so-called hydrop
hobins. In P. tinctorius, the content of hydrophobin transcripts is hi
gh in aerial hyphae and during the ectomycorrhizal sheath formation. A
lteration of cell walls and the extracellular matrix is therefore a ke
y event in the ectomycorrhiza development. An understanding of the mol
ecular mechanisms that underlies the temporal and spatial control of g
enes and proteins involved in the development of the symbiotic interfa
ce is now within reach, as more sophisticated techniques of molecular
and genetic analysis are applied to the mycorrhizal interactions.