light sensing by fungi - ysucrcooper01.people.ysu.edu/biol 6949-fungal light sensing.pdf · biol...

BIOL 6949: Cellular and Molecular Mycology

Fall 2011

Lecture: Fungal Light Sensing 1

Light Sensing by Fungi

BIOL 6949 (Spring 2011) Copyright © 2011 Chester R. Cooper, Jr.

Disclaimer: This lecture slide presentation is intended solely for educational purposes. Many of the images contained herein are the property of the original owner, as indicated within the figure itself or within the figure legend. These images are used only for illustrative purposes within the context of this lecture material. Use of these images outside the purpose of this presentation may violate the rights of the original owner. Dr. Cooper and Youngstown State University assume no responsibility for the unauthorized use of the material contained herein.


Fungi and Light

•  Why benefit(s) do fungi derive from sensing light?

•  A common feature is the change in spore production in response to light

•  Linkage between light response and virulence •  Regulation of secondary metabolite production •  Effects on commercial mushroom cultivation •  Use photosystems in fungi as models for other

organisms that sense light


Fungi and Light (cont.)

•  Photosensory proteins are defined as proteins that regulate a signal transduction pathway in response to light

•  Not all fungi sense light –  Saccharomyces cerevisiae does not have an

established photosensor –  Light does affect various processes in S.

cerevisiae that are not dependent upon signal transduction, e.g., respiration is inhibited by blue light


Photosensors in fungi. Fig. 1 from Idnurm et al. 2010. Fungal Genetics and Biology 47: 881-892



•  Gold standard to prove photosensory function –  Observable light response –  Measure response over a range of wavelengths

(action spectrum) –  Identify a photosensor gene or protein –  Impaired response due to mutation in photosensor

gene –  Isolated protein must have same absorption

spectrum as action spectrum –  Protein function must explain observed behavior



•  Types of observable light response –  Light affects sporulation –  Light increases pigmentation –  Phototropic response –  Virulence

•  Light increases pathogenicity of Histoplasma capsulatum

•  Mutation in wc-1 decreases virulence in Cryptococcus neoformans and Fusarium oxysporum


Fall 2011



Overview of photoresponses in A. nidulans. Fig. 1 from Bayram et al. 2010. Fungal Genetics and Biology 47: 900-908



•  What if no response is observed? Does that mean the fungus has no photosensory system? –  Need to examine various “wild-type” strains, e.g.,

laboratory strain of Aspergillus nidulans most often used was a natural Ve1 mutant

–  Examine transcriptome changes in response to light

–  Examine proteome changes in response to light


Types of Photosensors

•  Major classes of photosensors include –  Opsins

•  Membrane-bound proteins with seven transmembrane alpha-helices that bind retinal

•  Role in photosensing is not clear •  Distribution among fungi is sporadic


Photosensors in fungi. Fig. 1 from Idnurm et al. 2010. Fungal Genetics and Biology 47: 881-892


Types of Photosensors (cont.)

•  Major classes of photosensors include (cont.) –  Phytochromes

•  Chromophore that senses red and far-red light •  Distribution among fungi is sporadic •  In A. nidulans, FphA protein is a phytochrome

that regulates asexual/sexual transition as well as secondary metabolite production in response to light

•  Function in other fungi is unknown


Types of Photosensors (cont.)

•  Major classes of photosensors include (cont.) –  Cryptochromes and photolyases

•  Sense blue/UV-A light •  Photolyases can repair DNA damage •  Cryptochromes cannot repair DNA damage, but

– Regulate growth and development – Cell signaling – Circadian rhythms


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White Collar

•  White Collar 1 (WC1) encoded by many fungi –  Senses blue and near UV light –  Interacts with White Collar 2 (WC2)

•  Roles of WC1 –  Circadian clock machinery of Neurospora crassa –  Sporulation –  Pigmentation –  Phototropism


White Collar (cont.)

•  Some examples of wc-1 homologs and their functions among fungi (see Table 1 in Indurm et al., 2010): –  Trichoderma atroviride – blr-1: conidiation –  Aspergillus nidulans – lreA: asexual/sexual

reproduction; mycotoxin biosynthesis –  Fusarium oxysporum – blr1: conidiation; virulence –  Phycomyces blakesleeanus – madA:

phototropism; carotene biosynthesis; sporulation –  Coprinopsis cinerea – dst1: cap development



•  Structure of WC-1 –  Three PAS domains –  The N-terminal PAS = LOV (light, oxygen, voltage)

domain – functions in light sensing –  GATA class zinc finger at C-terminus – functions

as a transcription factor •  WC-1 is encoded by a gene (wc-1) that is

ancient and probably derived from a single origin


Phylogenetics of WC-1 in fungi. Fig. 3 from Idnurm et al. 2010. Fungal Genetics and Biology 47: 881-892


Photoreceptor proteins from N. crassa. Fig. 1 from Corrochano. 2007. Photochem. Photobiol. Sci. 7: 725-736


Scheme of the general architecture of the light receptors and other proteins implicated in the photoresponses of A. nidulans. Fig. 3 from Bayram et al. 2010. Fungal Genetics and Biology 47: 900-908


Fall 2011




•  White Collar 2 (WC-2) is a second photosensing protein found in most species –  Encoded by wc-2 in N. crassa –  WC-2 homologs are required for blue-light sensing

in basidiomycetes –  WC-1 and WC-2 form a complex by physically

interacting –  DNA binding domain of WC-2 is required for light-

induced transcription of the WC-1/WC-2 complex



•  LOV domain proteins –  Some ascomycetes also possess LOV domain

proteins –  In N. crassa, designated VIVID (or VVD) –  Acts as a second photosensory protein –  Unknown how these proteins modulate light in

signal transduction; targets are unknown


Quantification of conidiospores and cleistothecia formation in A. nidulans. Fig. 2 from Bayram et al. 2010. Fungal Genetics and Biology 47: 900-908


A simplified model for the photoactivation of gene expression by the WC complex. Fig. 2 from Corrochano. 2007. Photochem. Photobiol. Sci. 7: 725-736

light sensing by fungi - ysucrcooper01.people.ysu.edu/biol 6949-fungal light sensing.pdf · biol...

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