Light sensing in Aspergillus fumigatus highlights the case for establishing new models for fungal photobiology

Abstract

Microbes inhabit diverse environmental locations, and many species need to shift their physiology between different niches. To do this effectively requires the accurate sensing of and response to the environment. For pathogens, exposure to light is one major change between a free-living saprophyte lifestyle and causation of disease within the host. However, how light may act as a signal to influence pathogenesis, on the side of either the host or the pathogen, is poorly understood. Research during the last 2 decades has uncovered aspects about the machinery for light sensing in a small number of fungi. Now, Fuller et al. have initiated studies into the role that light and two photosensor homologs play in the behavior of the ubiquitous fungal pathogen Aspergillus fumigatus [K. K. Fuller, C. S. Ringelberg, J. J. Loros, and J. C. Dunlap, mBio 4(2):e00142-13, 2013, doi:10.1128/mBio.00142-13]. Light represses the germination of A. fumigatus spores and enhances resistance to ultraviolet light, oxidative stresses, and cell wall perturbations. The phenotypes of the strains with mutations in the LreA and FphA homologs revealed that these sensors control some, but not all, responses to light. Furthermore, interactions occur between blue and red light signaling pathways, as has been described for a related saprophytic species, Aspergillus nidulans. Genome-wide transcript analyses found that about 2.6% of genes increase or decrease their transcript levels in response to light. This use of A. fumigatus establishes common elements between model filamentous species and pathogenic species, underscoring the benefits of extending photobiology to new species of fungi.

FIG 1

Fungi that have emerged or are emerging as models for research on sensing and response to light. The phylogeny (partial 18S rDNA) divides the species into the Ascomycota (red), Basidiomycota (blue), and Mucoromycotina (green). All nine species have saprophytic growth capabilities, and some can also cause disease. Wavelengths with a characterized response are red (R) or blue (B). Useful features in photobiology research or behavior modified by light for individual species are listed. Common research directions in these species can provide a better understanding of how light influences fungal biology.