Carbon source dependence of conidiation and its photostimulation in Hypocrea atroviridis
Friedl, M. A., Kubicek, C. P. and I. S. Druzhinina, 2008
AEM, 74:1, 245-250
Hypocrea atroviridis is frequently used as a photomorphogenetic model due to itsability to conidiate upon exposure to light. Light is thereby believed to be the primary trigger for spore formation. In contrast, we show here that conidiation is primary carbon source dependent while illumination plays a catalytic role: from a total of 95 tested carbon sources, only a small set of carbohydrates, polyols and sugar acids allow conidiation in darkness, and on most of them it is significantly stronger expressed in light. In addition, there is also a number of carbon sources on which H. atroviridis conidiates in darkness but light does not further stimulate the process. Yet on another small set of carbon sources (l-sorbitol, d-fucose, d- and l-arabinose, erythritol), H. atroviridis shows better sporulation in darkness then in light. No sporulation was observed on organic acids and amino acids. Deletion mutants in the two blue light receptor proteins BLR-1 and BLR-2 generally showed weaker conidiation on a smaller number of carbon sources, yet they clearly sporulated on 15 and27 of the 95 carbon sources tested, respectively. Of them, only 11 carbon sources supported conidiation in both mutants suggesting a different involvement of the BLR-1 and BLR-2 receptors in the carbon source-dependent regulation of spore formation. Addition of cyclic AMP, which has been reported to lead to conidiation in the darkness, both positively and negatively effected sporulation, and resulted in different effects in the parental strain and the two Δblr mutants. Our data show that the carbon source is the prime determinant for conidiation, and that it influences its regulation by BLR-1 and BLR-2 and their cross-talk with cAMP.