Molecular Complex Essential For Vision Identified In Fungi

The results were published recently in the Proceedings of the National Academy of Sciences by the team, which includes Prof. Luis M. Corrochano and Dr. Julio Rodríguez Romero, from the Department of Genetics of the University of Seville, Spain, in collaboration with colleagues from Duke University and the University of Missouri at Kansas City (USA), Glasgow University (UK), and the University of Salamanca (Spain).

The fungus Phycomyces blakesleeanus is used in the laboratory to investigate how organisms perceive signals from the environment. The fruiting body of Phycomyces is sensitive to many environmental stimuli, including light, gravity, wind, and the presence of nearby objects. These signals modify the speed and direction of growth of the Phycomyces fruiting body. Like plants, Phycomyces grows upwards towards light.

The isolation and characterization of Phycomyces blind mutants unable to move towards light was initiated in the seventies of the last century in the laboratory of Nobel laureate Max Delbrück. The mutants, named mad, have been investigated in detail for several decades and have been used to investigate the molecular basis of vision in microorganisms using Phycomyces as a model. However, the molecular nature of the mad genes remained elusive until recently.

In a previous work published in 2006, the team of Spanish and American scientists identified and characterized the madA gene, and proposed that the corresponding protein could sense photons as a photoreceptor and could bind to DNA to regulate genes activity. The new research shows that the product of the gene madB is a putative DNA-binding protein that interacts with the product of the madA gene to create a protein complex. The scientists propose that this complex regulates the activities of genes after the reception of light. The scientists further propose that this fungus uses this protein complex to perceive light and to change the direction of growth of its fruiting body, to regulate development of its fruiting bodies, and to activate the synthesis of beta-carotene, an anti-oxidant compound that accumulates in the cell when exposed to light.

In addition, the team of scientists has identified several genes similar to madA and madB in the genome of Phycomyces that may explain the extraordinary sensitivity to light of this fungus, similar to that of the human eye.

The identification and characterization of madA and madB genes will help to understand in more detail the mechanisms that regulate the responses of fungi and other organisms to daily changes in lighting conditions in nature.