Light inhibits spore germination through phytochrome in Aspergillus nidulans.

Aspergillus nidulans responds to light in several aspects. The balance between sexual and asexual development as well as the amount of secondary metabolites produced is controlled by light. Here, we show that germination is largely delayed by blue (450 nm), red (700 nm), and far-red light (740 nm). The largest effect was observed with far-red light. Whereas 60 % of the conidia produced a germ tube after 20 h in the dark, less than 5 % of the conidia germinated under far-red light conditions. Because swelling of conidia was not affected, light appears to act at the stage of germ-tube formation. In the absence of nutrients, far-red light even inhibited swelling of conidia, whereas in the dark, conidia did swell and germinated after prolonged incubation. The blue-light signaling components, LreA (WC-1) and LreB (WC-2), and also the cryptochrome/photolyase CryA were not required for germination inhibition. However, in the phytochrome mutant, ∆fphA, the germination delay was released, but germination was delayed in the dark in comparison to wild type. This suggests a novel function of phytochrome as far-red light sensor and as activator of polarized growth in the dark.