European temperate forests (such as to tropical forests or to plant species other than trees). Moreover, if seed-dispersing animals are as crucial to the persistence of plants as this and other studies suggest (28, 29), then the combination of habitat loss with direct and indirect removal of animals, to which many of the world's most diverse forests are subject, is likely to have more drastic effects than either perturbation alone. In these circumstances, animaldispersed species might be more, not less, sensitive to habitat loss. This points to the maintenance of the network of plant-animal interactions as a cornerstone of conservation policy and to the need for more studies of species responses to habitat loss. Differentiation and secondary metabolism are correlated processes in fungi that respond to light. In Aspergillus nidulans, light inhibits sexual reproduction as well as secondary metabolism. We identified the heterotrimeric velvet complex VelB/VeA/LaeA connecting light-responding developmental regulation and control of secondary metabolism. VeA, which is primarily expressed in the dark, physically interacts with VelB, which is expressed during sexual development. VeA bridges VelB to the nuclear master regulator of secondary metabolism, LaeA. Deletion of either velB or veA results in defects in both sexual fruiting-body formation and the production of secondary metabolites.

VeA is the founding member of the velvet superfamily of fungal regulatory proteins. This protein is involved in light response and coordinates sexual reproduction and secondary metabolism in Aspergillus nidulans. In the dark, VeA bridges VelB and LaeA to form the VelB-VeA-LaeA (velvet) complex. The VeA-like protein VelB is another developmental regulator, and LaeA has been known as global regulator of secondary metabolism. In this study, we show that VelB forms a second light-regulated developmental complex together with VosA, another member of the velvet family, which represses asexual development. LaeA plays a key role, not only in secondary metabolism, but also in directing formation of the VelB-VosA and VelB-VeA-LaeA complexes. LaeA controls VeA modification and protein levels and possesses additional developmental functions. The laeA null mutant results in constitutive sexual differentiation, indicating that LaeA plays a pivotal role in inhibiting sexual development in response to light. Moreover, the absence of LaeA results in the formation of significantly smaller fruiting bodies. This is due to the lack of a specific globose cell type (Hülle cells), which nurse the young fruiting body during development. This suggests that LaeA controls Hülle cells. In summary, LaeA plays a dynamic role in fungal morphological and chemical development, and it controls expression, interactions, and modification of the velvet regulators.

Fruit body formation in filamentous fungi is a complex and yet hardly understood process. We show here that protein turnover control is crucial for Aspergillus nidulans development. Deletion of genes encoding COP9 signalosome (CSN) subunits 1, 2, 4, or 5 resulted in identical blocks in fruit body formation. The CSN multiprotein complex controls ubiquitin-dependent protein degradation in eukaryotes. Six CSN subunits interacted in a yeast two-hybrid analysis, and the complete eight-subunit CSN was recruited by a functional tandem affinity purification tag fusion of subunit 5 (CsnE). The tagged CsnE was unable to recruit any CSN subunit in a strain deleted for subunit 1 or subunit 4. Mutations in the JAMM metalloprotease core of CsnE resulted in mutant phenotypes identical to those of csn deletion strains. We propose that a correctly assembled CSN including a functional JAMM links protein turnover to fungal sexual development.development ͉ filamentous fungi F ungal fruit bodies are sexual reproduction structures that generate meiotic spores. The model mold Aspergillus nidulans develops a closed spherical fruit body (cleistothecium) including different tissue types: Hülle cells surround and nurse the growing cleistothecium, pericarp cells develop the protecting wall, and inner ascogenous cells mature into sexual spores (1, 2). Massive reconstruction of vegetative hyphae is required to build the complex three-dimensional fruit body. The regulation of this development is hardly understood in any fungus (3). A genetic screen recently identified csnD and csnE resembling genes for subunits of the COP9 signalosome (CSN) of animals and plants to be essential for fruit body formation of A. nidulans (4).CSN is a multiprotein complex composed of proteins containing PCI and MPN interaction domains (5, 6). Csn5/Jab1 is the only subunit conserved in all eukaryotes, and it carries an MPNϩ domain containing the JAMM motif conferring metalloprotease (deneddylation) activity (6, 7). CSN controls by its MPNϩ domain the activity of cullin-RING E3 ligases by cleaving the ubiquitin-like protein Nedd8/Rub1 from the cullin (8, 9). Neddylated E3 ubiquitin ligases are key mediators of posttranslational labeling of proteins for the proteasome (10). The CSN thus controls eukaryotic ubiquitin-dependent protein degradation.The complete eight-subunit CSN, composed of six PCI and two MPN domain proteins, was described for eukaryotes as humans (11), mice (12), plants (13), flies (14), and Dictyostelium (15). In fungi, definitive evidence for an eight-subunit CSN is lacking so far. CSN complex purification from Neurospora crassa revealed subunits 1-7, but subunit 8 was identified neither in the purification experiment nor in the genome sequence by bioinformatics means (16). In fission yeast subunits 6 and 8 have not been identified yet (17), and in the CSN-related complex of Saccharomyces cerevisiae only subunit Csn5 (yeast Rri1p) is well conserved (18).The fungal CSN complexes known to date are not essential for viability but are involved in cellu...