Hydrophobins are small
extracellular proteins, unique to and ubiquitous in
filamentous fungi, which mediate interactions between the
fungus and environment. The mycoparasitic
fungus Hypocrea atroviridis has recently been shown to possess 10 different class II
hydrophobin genes, which is a much higher number than that of any other
ascomycete investigated so far. In order to learn the potential advantage of this
hydrophobin multiplicity for the
fungus, we have investigated their expression patterns under different physiological conditions (e.g., vegetative growth), various conditions inducing
sporulation (light,
carbon starvation, and mechanical injury-induced stress), and confrontation with potential hosts for mycoparasitism. The results show that the 10
hydrophobins display different patterns of response to these conditions: one
hydrophobin (encoded by hfb-2b) is constitutively induced under all conditions, whereas other
hydrophobins were formed only under conditions of
carbon starvation (encoded by hfb-1c and hfb-6c) or light plus
carbon starvation (encoded by hfb-2c, hfb-6a, and hfb-6b). The
hydrophobins encoded by hfb-1b and hfb-5a were primarily formed during vegetative growth and under mechanical injury-provoked stress. hfb-22a was not expressed under any conditions and is likely a
pseudogene. None of the 10 genes showed a specific expression pattern during mycoparasitic interaction. Most, but not all, of the expression patterns under the three different conditions of
sporulation were dependent on one or both of the two blue-light
regulator proteins BLR1 and BLR2, as shown by the use of respective
loss-of-function mutants. Matrix-assisted
laser desorption ionization-time of flight
mass spectrometry of mycelial
solvent extracts provided sets of molecular
ions corresponding to HFB-1b, HFB-2a, HFB-2b, and HFB-5a in their oxidized and processed forms. These in silico-deduced sequences of the
hydrophobins indicate cleavages at known
signal peptide sites as well as additional N- and
C-terminal processing. Mass peaks observed during confrontation with plant-pathogenic
fungi indicate further
proteolytic attack on the
hydrophobins. Our study illustrates both divergent and redundant functions of the 10
hydrophobins of H. atroviridis.
