A novel light-sensing protein in the fungal species Blastocladiella emersonii.

The fungal eye

Researchers at the University of Exeter and São Paulo University, Brazil  have discovered a new light-sensing mechanism in a fungus, which is similar to that found in the human eye.

In this study, University of Exeter researcher Dr Thomas Richards and collaborators in São Paulo found a novel light-sensing protein in the fungal species Blastocladiella emersonii. The research, recently published in Current Biology, describes a light-sensing protein- rhodopsin which is fused to a guanylyl cyclase protein as one single multi-functional protein. This novel protein therefore acts both as a light sensor and as system to manufacture chemical signals which trigger cell functions.

Scientists have long known that some fungi use rhodopsin to detect light and guide the direction these fungi swim; with the help of other proteins, light received by rhodopsin triggers the fungal cell to move. A similar event happens in the human eye, but the light signal is converted into a neural signal interpreted by the brain as an image rather than a trigger for cellular movement, as is the case for these fungi.

This difference in light signal conversion between humans and fungi is down to a group of what was previously considered to be animal-specific proteins, which  function with rhodopsin in the human eye – guanylyl cyclase is one of these proteins.

This study has shown that these light-sensing proteins, function within a specific spherical sub-cellular compartment. Tom Richards commented, “it was very exciting when we realised that this protein system localised to a specific –oil filled- organ within the cell, it was like we were looking at a fungal eye.”

This study also illustrated that fungi have evolved this light sensing system quite recently in evolutionary history, long after the split between the animal and fungal lineage hundreds of million years ago. “This group of fungi have assembled a system for light perception that functions in a similar manner to that which functions in animals, essentially using the same components but coming up with a new mechanism for detecting light” said Dr Richards.

This discovery may provide an excellent opportunity to investigate two key proteins involved in human vision in a fungus, a useful model system. Since light signal transduction in this fungus culminates in movement, this model system comes with an easy-to-quantify way to measure the functions of these important proteins and may also provide new possibilities in understanding the genes that control light sensing and visual perception.

Date: 3 June 2014

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