Localization and stability of the velvet protein VE-1 and its orthologous VeA in Neurospora crassa

The Velvet regulators are a family of proteins with a conserved domain that help to coordinate fungal growth, differenciation and secondary metabolism in fungi. In Aspergillus nidulans VeA is a light-dependent developmental regulator that activates sexual development and inhibits conidiation. Mutations in veA results in constitutive conidiation that is independent of light, and VeA forms a complex with photoreceptors. The Neurospora crassa genome contains a homolog of veA, ve-1, that encodes a protein, VE-1, with a nuclear localization sequence. The ve-1 mutant has defects in aerial hyphal growth and increased conidiation.

We have characterized the localization and stability of VE-1 using a strain with a tagged version of VE-1. We detected VE-1 in vegetative mycelia and in aerial hyphae during conidial development when the fungus was grown in the light. In the dark, however, VE-1 was detected in vegetative hyphae and was absent in aerial hyphae despite the presence of ve-1 mRNA. We characterized the stability of VE-1 in a series of mutants in the protein degradation pathway and with a chemical inhibitor of the proteasome. We propose that the absence of VE-1 in aerial hyphae in the dark is due to VE-1 degradation through the proteasome with FWD-1 acting as an adaptor protein during this process.

To investigate if the regulation by light of VE-1 stability was present in other fungi we have cloned a tagged version of the A. nidulans veA gene in N. crassa. The new strain will allow us to characterize the stability and localization of the A. nidulans protein in N. crassa and to identify possible conserved regulatory mechanisms between the two fungi.