In all of nature, scientists have discovered only six different mechanisms by which organisms sense light, and only one of these mechanisms can detect ultraviolet light (the rhodopsins that sense ultraviolet light in non-mammalian vertebrates). The widely studied model organism Caenorhabditis elegans has none of the known light transduction systems, but we discovered that C. elegans has a robust locomotory response to ultraviolet light. C. elegans may use this light response to escape damaging or lethal doses of sunlight. Ultraviolet and other shortwave light, such as violet and blue wavelengths, drive locomotion by bypassing two critical signals, cyclic adenosine monophosphate (cAMP) and diacylglycerol (DAG), that neurons use to shape and control behaviors. C. elegans mutants lacking these signals are paralyzed and unresponsive to harsh physical stimuli in ambient light, but short-wavelength light rapidly rescues their paralysis and restores greater-than-normal levels of coordinated locomotion. This astonishing light response is mediated by a novel ultraviolet light receptor that acts in neurons. Our results reveal a novel molecular solution for ultraviolet light detection and an unusual sensory modality in C. elegans that is unlike any previously described light response in any organism.

PLoS Biol 6(8): e198 doi:10.1371/journal.pbio.0060198