Species of the mycoparasitic fungal genus Hypocrea/Trichoderma are prominent producers of
peptaibols, a class of small linear
peptides of fungal origin. Some of these
peptaibols have been shown to act synergistically with cell-wall-degrading
enzymes in the inhibition of the growth of other fungi in vitro and in vivo. Here we present the structure of the Hypocrea atroviridis
peptaibol synthetase gene (pbs1), deduced from the genome sequence of H. atroviridis. It consists of 19 typical
peptide synthetase modules with the required additional modifying domains at the N and C termini. Phylogenetic and similarity analyses of the individual
amino acid-activating modules is consistent with its ability to synthesize
atroviridins. Matrix-assisted
laser desorption ionization-time of flight mass spectrometry of surface-grown cultures of H. atroviridis showed that no
peptaibols were formed during vegetative growth, but a microheterogenous mixture of
atroviridins accumulated when the colonies started to sporulate. This correlation between sporulation and
atroviridin formation was shown to be independent of the pathway inducing sporulation (i.e., light, mechanical injury and
carbon starvation, respectively).
Atroviridin formation was dependent on the function of the two blue light regulators, BLR1 and BLR2, under some but not all conditions of sporulation and was repressed in a pkr1 (regulatory subunit of
protein kinase A) antisense strain with constitutively active
protein kinase A. Conversely, however, loss of function of the Galpha-
protein GNA3, which is a negative regulator of sporulation and leads to a hypersporulating phenotype, fully impairs
atroviridin formation. Our data show that formation of
atroviridin by H. atroviridis occurs in a sporulation-associated manner but is uncoupled from it at the stage of GNA3.