Light inhibits spore germination through phytochrome in Aspergillus nidulans
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RESEARCH ARTICLE
Light inhibits spore germination through phytochrome in Aspergillus nidulans Julian Ro¨hrig • Christian Kastner • Reinhard Fischer
Received: 10 December 2012 / Revised: 2 January 2013 / Accepted: 4 January 2013 Ó Springer-Verlag Berlin Heidelberg 2013
Abstract 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, DfphA, the germination delay was released, but germination was delayed in the dark in comparison to wild type. This suggests a novel function of
Communicated by U. Kueck. J. Ro¨hrig and C. Kastner contributed equally. J. Ro¨hrig C. Kastner R. Fischer (&) Department of Microbiology, Institute for Applied Biosciences, Karlsruhe Institute of Technology (KIT), Hertzstrasse 16, 76187 Karlsruhe, Germany e-mail: [email protected] URL: www.iab.kit.edu Present Address: C. Kastner Henkel AG and Co. KGaA, VSA-Corporate Analytics, Microbiology and Product Safety, Henkelstr 67, 40191 Du¨sseldorf, Germany
phytochrome as far-red light sensor and as activator of polarized growth in the dark. Keywords Aspergillus Phytochrome White collar Light sensing Germination
Introduction Filamentous fungi are extremely versatile organisms, which can grow under very different environmental conditions. They are able to sense various physical parameters and translate them into cellular responses, such as adaptation to osmotic stress or nutrient availability. One major response triggered by environmental conditions is the developmental decision. For instance, the ascomycete Aspergillus nidulans grows as hyphae in substrates, develops asexually when it grows at a water–air interface in light and develops complex sexual fruiting bodies when grown in the dark (Adams 1994; Busch and Braus 2007; Rodriguez-Romero et al. 2010). Both types of spores, conidia and ascospores, which are produced in these morphogenetic pathways are well protected against harmful UV light by pigments embedded into the cell wall. Spores are thus well adapted to spreading in the environment. However, once spores land on a nutrient-rich surface, vegetative hyphae are going to be produced. These hyphae are much less well adapted for growth in the pre
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