Abstract:
Surface fibrils (fimbriae) have been observed on fungi from every major
group. Fimbriae are thought to be involved in the following cell to cell
interactions: conjugation, flocculation and adhesion. Several higher fungi
exibit two other types of interactions: hyphal fusion (anastomosis) and
clamp connection formation. As a prelude to examining the role of
fimbriae in these processes, the fimbriae of two fungi that undergo these
fusion events were examined.
Electron microscopy studies revealed that Coprinus cinereus and
Schizophyllum commune are fimbriated. C. cinereus fimbriae were 5 nm
in diameter and 0.5 to 20 11m in length. Fimbriae of C. cinereus oidia were
more numerous and longer than those of the hyphal stage. S. commune
fimbriae were also 5 nm in diameter, but were only 0.5 to 2 11m in length.
There was an unequal distribution of fimbriae on the hyphal surfaces of S.
commune . Fimbriae were sparsely distributed over the entire hyphal
surface, with higher densities of fibrils present on the side growths of the
hyphae found in the older sections of the mycelium.
Antiserum raised against Ustilago violacea fimbrial protein (AU) crossreacted
strongly with 37 and 39 kd C. cinereus mycelial proteins. In
contrast, AU bound very weakly to 89 and 92 kd S. commune mycelial
proteins. Since AU cross-reacted poorly with S. commune fimbrial
proteins, it was impossible to further characterize the fimbriae of this
specIes. The 37 and 39 kd C. cinereus proteins, were isolated by
electroelution and were shown to be able to form fibrils the same diameter
as oidial fimbriae. The 37 kd protein was shown to be composed of several
proteins with isoelectric points ranging from pH 6.1 to 7.63. Furthermore,
the 37 kd protein was found to be multimeric, while the 39 kd protein was
not. These results strongly suggested that the 37 kd protein is the
structural fimbrial protein of C. cine reus .
Finally, a series of experiments were designed to determine whether
fimbriae are required for conjugation in U. violacea Conjugation was
inhibited significantly with AU, but not with pre-immune serum or AU
preincubated with purified fimbrial protein. Thus, it was concluded that
fimbriae play a central role in mating in this organism.
