Fungi, Hidden in Soil or Up in the Air: Light Makes a Difference

Abstract

Light is one of the most important environmental factors for orientation of almost all organisms on Earth. Whereas light sensing is of crucial importance in plants to optimize light-dependent energy conservation, in nonphotosynthetic organisms, the synchronization of biological clocks to the length of a day is an important function. Filamentous fungi may use the light signal as an indicator for the exposure of hyphae to air and adapt their physiology to this situation or induce morphogenetic pathways. Although a yes/no decision appears to be sufficient for the light-sensing function in fungi, most species apply a number of different, wavelength-specific receptors. The core of all receptor types is a chromophore, a low-molecular-weight organic molecule, such as flavin, retinal, or linear tetrapyrrols for blue-, green-, or red-light sensing, respectively. Whereas the blue-light response in fungi is one of the best-studied light responses, all other light-sensing mechanisms are less well studied or largely unknown. The discovery of phytochrome in bacteria and fungi in recent years not only advanced the scientific field significantly, but also had great impact on our view of the evolution of phytochrome-like photoreceptors.

Diatom Phytochromes Reveal the Existence of Far-Red-Light-Based Sensing in the Ocean

“…Subsequently, these photoreceptors have been identified in several prokaryotic and eukaryotic organisms, from phototrophs to heterotrophs (Rodriguez-Romero et al, 2010;Auldridge and Forest, 2011).…”

Structure of the Cyanobacterial Phytochrome 2 Photosensor Implies a Tryptophan Switch for Phytochrome Signaling

“…Phytochromes are red/far-red light absorbing photoreceptors first discovered in plants (1), and later in many photosynthetic and non-photosynthetic bacteria (2) as well as in several fungi (3). A hallmark of these photochromic light sensors is their bilin chromophore covalently bound to a cGMP phosphodiesterase/adenylyl cyclase/FhlA (GAF) 2 domain.…”

Role of the Alternaria alternata Blue-Light Receptor LreA (White-Collar 1) in Spore Formation and Secondary Metabolism

“…These observations suggest that Alternaria species are able to sense and respond to light. It has been well established, meanwhile, that many fungi are able to respond to light and employ one or several photoreceptors (10)(11)(12). The existence of light receptors in filamentous fungi has been shown for Neurospora crassa, Aspergillus nidulans, Coprinus cinereus, Cryptococcus neoformans, Phycomyces blakesleeanus, and Physarum polycephalum and for many others.…”

“…Some of them possess receptors for blue, red, and green light and are therefore able to sense light over a broad spectral range. The perception of light in these fungi has been shown to influence asexual conidiation, sexual development, pigmentation, the circadian clock, and secondary metabolism (10,12). The blue-light response often seems to be the most important one; e.g., all light-dependent processes in N. crassa are regulated by UV or blue light (13,14).…”