The Aspergillus nidulans Velvet-interacting protein, VipA, is involved in light-stimulated heme biosynthesis

Filamentous fungi are able to differentiate morphologically and adapt the metabolism to internal and external cues. One major regulator is the so-called velvet protein, VeA, best studied in Aspergillus nidulans. The protein interacts with several other proteins to regulate light sensing, the balance between asexual and sexual development, penicillin biosynthesis or mycotoxin production. Here, we characterized a novel VeA-interacting protein, VipA. The 334 amino acid long protein comprises a FAR1-like DNA-binding domain, known from plant transcription factors like FHY3 (Far-red elongated hypocotyl 3). VipA interacted not only with VeA, but also with the WC orthologue LreA in the nuclei and with the phytochrome FphA in the cytoplasm. Conidia and cleistothecia formation was similarly affected in a vipA-deletion strain as in an fphA mutant. However, the effect was less pronounced, suggesting a modulating and not an essential role in light sensing. In addition, VipA modulated heme biosynthesis in response to light through association with the hemB promoter, the gene encoding 5-aminolevulinic acid dehydratase. After illumination of A. nidulans mycelia with white light the intracellular heme concentration increased by 30% in comparison to a vipA-deletion mutant. Hence, VipA couples heme biosynthesis to the illumination conditions.