Photoresponsive fungi modulate their development and metabolism in response to light, with many species reproducing sexually and synthesizing secondary metabolites such as toxins and antibiotics only in the dark. In the mold Aspergillis nidulans , light inhibits the nuclear accumulation of Velvet (VeA), a negative regulator of asexual reproduction and antibiotic synthesis. Bayram et al. report that VeA contributes to this light-regulated switch through its interactions with the closely related velvet-like protein VelB, the secondary metabolism master regulator LaeA, and the nuclear importin KapA. VeA and VelB, both of which were required for sexual development, associated with one another in the nucleus and in the cytoplasm. The association between VeA and VelB was independent of light input, but the abundance of VeA greatly decreased in the light. In the dark, VeA and VelB formed a heterotrimeric nuclear complex with the methyltransferase LaeA. VelB and LaeA did not interact with one another directly, but both bound directly to VeA. The authors suggest a model in which, in the dark, VelB/VeA heterodimers form in the cytoplasm and translocate into the nucleus with the help of KapA. In the nucleus, the VelB/VeA heterodimers associate with LaeA to form a heterotrimeric complex that regulates the expression of secondary metabolite genes. It is not clear how light reduces the abundance of VeA, but the formation of the nuclear VelB/VeA/LaeA heterotrimeric complex provides the first clues as to how sexual development and metabolism are coordinated by light. Commentary by Fischer places this study in the greater context of fungal biology. Ö. Bayram, S. Krappmann, M. Ni, J. W. Bok, K. Helmstaedt, O. Valerius, S. Braus-Stromeyer, N.-J. Kwon, N. P. Keller, J.-H. Yu, G. H. Braus, VelB/VeA/LaeA complex coordinates light signal with fungal development and secondary metabolism. Science 320 , 1504-1506 (2008). [Abstract] [Full Text] R. Fischer, Sex and poison in the dark. Science 320 , 1430-1431 (2008). [Summary] [Full Text]